LinuxLists.cc - [PATH 0/4] [RFC] Support virtual DRM

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Subject: [PATH 4/4] doc-rst: Add virtual DRM documentation

Signed-off-by: Tomohito Esaki <[email protected]>
---
Documentation/gpu/drivers.rst | 1 +
Documentation/gpu/vdrm.rst | 51 +++++++++++++++++++++++++++++++++++
2 files changed, 52 insertions(+)
create mode 100644 Documentation/gpu/vdrm.rst

diff --git a/Documentation/gpu/drivers.rst b/Documentation/gpu/drivers.rst
index b4a0ed3ca961..bad0226de972 100644
--- a/Documentation/gpu/drivers.rst
+++ b/Documentation/gpu/drivers.rst
@@ -19,6 +19,7 @@ GPU Driver Documentation
xen-front
afbc
komeda-kms
+ vdrm

.. only:: subproject and html

diff --git a/Documentation/gpu/vdrm.rst b/Documentation/gpu/vdrm.rst
new file mode 100644
index 000000000000..2ab1699c2f42
--- /dev/null
+++ b/Documentation/gpu/vdrm.rst
@@ -0,0 +1,51 @@
+=============================
+ drm/vdrm virtual DRM driver
+=============================
+
+Virtual DRM splits the overlay planes of a display controller into multiple
+virtual devices to allow each plane to be accessed by each process.
+
+This makes it possible to overlay images output from multiple processes on a
+display. For example, one process displays the camera image without compositor
+while another process overlays the UI.
+
+The virtual DRM creates standalone virtual device and make DRM planes from a
+master device (e.g. card0) accessible via one or more virtual device. However,
+these plane are no longer accessible from the original device.
+Each virtual device (and plane) can be accessed via a separate device file.
+
+The virtual DRM driver doesn't directly control the display hardware and has
+no access to the physical bus. Instead, the virtual DRM driver issues requests
+to the standard DRM device driver ("master" driver) when the hardware needs to
+be controlled. The master driver is modified to notify the virtual DRM driver
+of interrupt events from the display hardware.
+
+Plane position and size
+=======================
+The initial position, size and z-position of the plane used in virtual DRM is
+specified in the device tree. The position and size of the planes are set as
+properties and can be updated. The name of each property is as
+follows:
+* vdrm_offset_x: x-coordinate of the left-top of the plane on the screen
+* vdrm_offset_y: y-coordinate of the left-top of the plane on the screen
+* vdrm_width: width of the plane
+* vdrm_height: height of the plane
+
+Virtual DRM Functions Reference
+===============================
+
+.. kernel-doc:: drivers/gpu/drm/vdrm/vdrm_api.h
+ :internal:
+
+.. kernel-doc:: drivers/gpu/drm/vdrm/vdrm_drv.c
+ :export:
+
+Driver limitations
+==================
+1. Each virtual DRM device only supports one plane per CRTC.
+
+2. Virtual DRM doesn't support hot plug connector.
+
+3. If virtual DRM has multiple CRTCs, the initial position and size of the
+ virtual DRM planes is the same for all planes, since they cannot be set
+ for each plane in the device tree.
--
2.25.1

2021-06-21 06:31:54

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Subject: [PATH 3/4] dt-bindings: display: Add virtual DRM

Add device tree bindings documentation for virtual DRM.

Signed-off-by: Tomohito Esaki <[email protected]>
---
.../devicetree/bindings/display/vdrm.yaml | 67 +++++++++++++++++++
1 file changed, 67 insertions(+)
create mode 100644 Documentation/devicetree/bindings/display/vdrm.yaml

diff --git a/Documentation/devicetree/bindings/display/vdrm.yaml b/Documentation/devicetree/bindings/display/vdrm.yaml
new file mode 100644
index 000000000000..6493bb0fc09f
--- /dev/null
+++ b/Documentation/devicetree/bindings/display/vdrm.yaml
@@ -0,0 +1,67 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/display/vdrm.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Virtual DRM Device Tree Bindings
+
+description:
+ This document defines device tree properties virtual DRM. The initial
+ position, size and z-position of the plane used in the virtual DRM is
+ specified.
+ The current limitation is that these settings are applied to all crtc.
+
+properties:
+ compatible:
+ const: virt-drm
+
+patternProperties:
+ "^plane(@.*)?$":
+ description: Information of the planes used in virtual DRM
+ type: object
+
+ properties:
+ x:
+ type: int
+ description: x-coordinate of the left-top of the plane in pixels
+
+ y:
+ type: int
+ description: y-coordinate of the left-top of the plane in pixels
+
+ width:
+ type: int
+ description: width of the plane in pixels
+
+ height:
+ type: int
+ description: height of the plane in pixels
+
+ zpos:
+ type: int
+ description: z-position of the plane
+
+ required:
+ - x
+ - y
+ - width
+ - height
+ - zpos
+
+required:
+ - compatible
+ - "^plane(@.*)?$"
+
+examples:
+ - |
+ vdrm@0 {
+ compatible = "virt-drm";
+ plane@0 {
+ x = <200>;
+ y = <100>;
+ width = <800>;
+ height = <600>;
+ zpos = <1>;
+ };
+ };
--
2.25.1

2021-06-21 06:31:59

by Enrico Weigelt, metux IT consult

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Subject: [PATH 2/4] rcar-du: Add support virtual DRM device

In order to use vDRM, it is necessary that the vDRM device is registered
to du decice in the device tree.
The "vdrms" key is added in du node and the vDRM device node is specified.
For example:
----------
& du {
...
vdrms = <&vdrm0>;
};
----------

Signed-off-by: Tomohito Esaki <[email protected]>
---
drivers/gpu/drm/rcar-du/Kconfig | 4 +
drivers/gpu/drm/rcar-du/Makefile | 1 +
drivers/gpu/drm/rcar-du/rcar_du_crtc.c | 42 ++++++
drivers/gpu/drm/rcar-du/rcar_du_crtc.h | 13 ++
drivers/gpu/drm/rcar-du/rcar_du_drv.c | 13 ++
drivers/gpu/drm/rcar-du/rcar_du_drv.h | 3 +
drivers/gpu/drm/rcar-du/rcar_du_vdrm.c | 191 +++++++++++++++++++++++++
drivers/gpu/drm/rcar-du/rcar_du_vdrm.h | 67 +++++++++
drivers/gpu/drm/rcar-du/rcar_du_vsp.c | 22 +++
drivers/gpu/drm/rcar-du/rcar_du_vsp.h | 1 +
10 files changed, 357 insertions(+)
create mode 100644 drivers/gpu/drm/rcar-du/rcar_du_vdrm.c
create mode 100644 drivers/gpu/drm/rcar-du/rcar_du_vdrm.h

diff --git a/drivers/gpu/drm/rcar-du/Kconfig b/drivers/gpu/drm/rcar-du/Kconfig
index b47e74421e34..6747f69c8593 100644
--- a/drivers/gpu/drm/rcar-du/Kconfig
+++ b/drivers/gpu/drm/rcar-du/Kconfig
@@ -50,3 +50,7 @@ config DRM_RCAR_WRITEBACK
bool
default y if ARM64
depends on DRM_RCAR_DU
+
+config DRM_RCAR_DU_VDRM
+ tristate "Virtual DRM for R-Car DU"
+ depends on DRM_RCAR_DU && DRM_VDRM
diff --git a/drivers/gpu/drm/rcar-du/Makefile b/drivers/gpu/drm/rcar-du/Makefile
index 4d1187ccc3e5..b589b974a9f3 100644
--- a/drivers/gpu/drm/rcar-du/Makefile
+++ b/drivers/gpu/drm/rcar-du/Makefile
@@ -14,6 +14,7 @@ rcar-du-drm-$(CONFIG_DRM_RCAR_LVDS) += rcar_du_of.o \
rcar_du_of_lvds_r8a7796.dtb.o
rcar-du-drm-$(CONFIG_DRM_RCAR_VSP) += rcar_du_vsp.o
rcar-du-drm-$(CONFIG_DRM_RCAR_WRITEBACK) += rcar_du_writeback.o
+rcar-du-drm-$(CONFIG_DRM_RCAR_DU_VDRM) += rcar_du_vdrm.o

obj-$(CONFIG_DRM_RCAR_CMM) += rcar_cmm.o
obj-$(CONFIG_DRM_RCAR_DU) += rcar-du-drm.o
diff --git a/drivers/gpu/drm/rcar-du/rcar_du_crtc.c b/drivers/gpu/drm/rcar-du/rcar_du_crtc.c
index ea7e39d03545..7d48db24090b 100644
--- a/drivers/gpu/drm/rcar-du/rcar_du_crtc.c
+++ b/drivers/gpu/drm/rcar-du/rcar_du_crtc.c
@@ -32,6 +32,11 @@
#include "rcar_du_vsp.h"
#include "rcar_lvds.h"

+#include "rcar_du_vdrm.h"
+#ifdef CONFIG_DRM_RCAR_DU_VDRM
+#include "../vdrm/vdrm_api.h"
+#endif
+
static u32 rcar_du_crtc_read(struct rcar_du_crtc *rcrtc, u32 reg)
{
struct rcar_du_device *rcdu = rcrtc->dev;
@@ -1293,5 +1298,42 @@ int rcar_du_crtc_create(struct rcar_du_group *rgrp, unsigned int swindex,

rcar_du_crtc_crc_init(rcrtc);

+ INIT_LIST_HEAD(&rcrtc->vdrm_displays);
+ ret = rcar_du_vdrm_crtc_init(rcrtc, swindex);
+ if (ret < 0) {
+ dev_err(rcdu->dev,
+ "failed to initialize crtc %u for vDRM\n", swindex);
+ return ret;
+ }
+
+ return 0;
+}
+
+int rcar_du_crtc_add_vdrm_display(struct rcar_du_crtc *rcrtc,
+ struct vdrm_display *vdisplay)
+{
+ struct rcar_du_vdrm_display *disp;
+
+ disp = kzalloc(sizeof(*disp), GFP_KERNEL);
+ if (!disp)
+ return -ENOMEM;
+
+ disp->display = vdisplay;
+ INIT_LIST_HEAD(&disp->head);
+ list_add_tail(&disp->head, &rcrtc->vdrm_displays);
+
return 0;
}
+
+void rcar_du_crtc_remove_vdrm_displays(struct rcar_du_crtc *rcrtc)
+{
+ struct rcar_du_vdrm_display *disp, *tmp;
+
+ if (!rcrtc->dev)
+ return;
+
+ list_for_each_entry_safe(disp, tmp, &rcrtc->vdrm_displays, head) {
+ list_del(&disp->head);
+ kfree(disp);
+ }
+}
diff --git a/drivers/gpu/drm/rcar-du/rcar_du_crtc.h b/drivers/gpu/drm/rcar-du/rcar_du_crtc.h
index 5f2940c42225..1f749f0061e5 100644
--- a/drivers/gpu/drm/rcar-du/rcar_du_crtc.h
+++ b/drivers/gpu/drm/rcar-du/rcar_du_crtc.h
@@ -21,6 +21,12 @@

struct rcar_du_group;
struct rcar_du_vsp;
+struct vdrm_display;
+
+struct rcar_du_vdrm_display {
+ struct vdrm_display *display;
+ struct list_head head;
+};

/**
* struct rcar_du_crtc - the CRTC, representing a DU superposition processor
@@ -43,6 +49,7 @@ struct rcar_du_vsp;
* @vsp: VSP feeding video to this CRTC
* @vsp_pipe: index of the VSP pipeline feeding video to this CRTC
* @writeback: the writeback connector
+ * @vdrm_displays: display list for virtual DRM
*/
struct rcar_du_crtc {
struct drm_crtc crtc;
@@ -73,6 +80,8 @@ struct rcar_du_crtc {
unsigned int sources_count;

struct drm_writeback_connector writeback;
+
+ struct list_head vdrm_displays;
};

#define to_rcar_crtc(c) container_of(c, struct rcar_du_crtc, crtc)
@@ -111,4 +120,8 @@ void rcar_du_crtc_finish_page_flip(struct rcar_du_crtc *rcrtc);

void rcar_du_crtc_dsysr_clr_set(struct rcar_du_crtc *rcrtc, u32 clr, u32 set);

+int rcar_du_crtc_add_vdrm_display(struct rcar_du_crtc *rcrtc,
+ struct vdrm_display *vdisplay);
+void rcar_du_crtc_remove_vdrm_displays(struct rcar_du_crtc *rcrtc);
+
#endif /* __RCAR_DU_CRTC_H__ */
diff --git a/drivers/gpu/drm/rcar-du/rcar_du_drv.c b/drivers/gpu/drm/rcar-du/rcar_du_drv.c
index bfbff90588cb..42f0f5e0144f 100644
--- a/drivers/gpu/drm/rcar-du/rcar_du_drv.c
+++ b/drivers/gpu/drm/rcar-du/rcar_du_drv.c
@@ -29,6 +29,7 @@
#include "rcar_du_kms.h"
#include "rcar_du_of.h"
#include "rcar_du_regs.h"
+#include "rcar_du_vdrm.h"

/* -----------------------------------------------------------------------------
* Device Information
@@ -552,6 +553,8 @@ static int rcar_du_remove(struct platform_device *pdev)
struct rcar_du_device *rcdu = platform_get_drvdata(pdev);
struct drm_device *ddev = &rcdu->ddev;

+ rcar_du_vdrms_fini(rcdu);
+
drm_dev_unregister(ddev);

drm_kms_helper_poll_fini(ddev);
@@ -584,6 +587,11 @@ static int rcar_du_probe(struct platform_device *pdev)
if (IS_ERR(rcdu->mmio))
return PTR_ERR(rcdu->mmio);

+ /* Initialize the vDRM device */
+ ret = rcar_du_vdrms_init(rcdu);
+ if (ret < 0)
+ return ret;
+
/* DRM/KMS objects */
ret = rcar_du_modeset_init(rcdu);
if (ret < 0) {
@@ -607,6 +615,11 @@ static int rcar_du_probe(struct platform_device *pdev)

drm_fbdev_generic_setup(&rcdu->ddev, 32);

+ /* Register the vDRM device */
+ ret = rcar_du_vdrms_register(rcdu);
+ if (ret)
+ DRM_WARN("Setup virtual device failed.\n");
+
return 0;

error:
diff --git a/drivers/gpu/drm/rcar-du/rcar_du_drv.h b/drivers/gpu/drm/rcar-du/rcar_du_drv.h
index 02ca2d0e1b55..327f3a250cbe 100644
--- a/drivers/gpu/drm/rcar-du/rcar_du_drv.h
+++ b/drivers/gpu/drm/rcar-du/rcar_du_drv.h
@@ -97,6 +97,9 @@ struct rcar_du_device {
unsigned int dpad0_source;
unsigned int dpad1_source;
unsigned int vspd1_sink;
+
+ struct vdrm_device **vdrms;
+ int num_vdrms;
};

static inline struct rcar_du_device *to_rcar_du_device(struct drm_device *dev)
diff --git a/drivers/gpu/drm/rcar-du/rcar_du_vdrm.c b/drivers/gpu/drm/rcar-du/rcar_du_vdrm.c
new file mode 100644
index 000000000000..1f09ead92418
--- /dev/null
+++ b/drivers/gpu/drm/rcar-du/rcar_du_vdrm.c
@@ -0,0 +1,191 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * rcar_du_vdrm.c -- R-Car Display Unit Virtual DRMs
+ *
+ * Copyright (C) 2021 Renesas Electronics Corporation
+ */
+
+#include <linux/of_device.h>
+
+#include <drm/drm_print.h>
+#include <drm/drm_atomic.h>
+#include <drm/drm_atomic_helper.h>
+#include <drm/drm_vblank.h>
+#include <drm/drm_fourcc.h>
+#include <drm/drm_gem_cma_helper.h>
+#include <drm/drm_gem_framebuffer_helper.h>
+#include <media/vsp1.h>
+
+#include "rcar_du_vdrm.h"
+#include "rcar_du_kms.h"
+#include "rcar_du_crtc.h"
+#include "rcar_du_vsp.h"
+
+static int rcar_du_vdrm_dumb_create(struct drm_file *file,
+ struct drm_device *dev,
+ struct drm_mode_create_dumb *args)
+{
+ /*
+ * TODO:
+ * This is Warkarround.
+ * In the future, this function will be removed.
+ * The vdrm will be modified to directly call the dumb_create
+ * callback of the du driver.
+ */
+ unsigned int min_pitch = DIV_ROUND_UP(args->width * args->bpp, 8);
+ unsigned int align;
+
+ /*
+ * The R8A7779 DU requires a 16 pixels pitch alignment as documented.
+ */
+ align = 16 * args->bpp / 8;
+
+ args->pitch = roundup(min_pitch, align);
+
+ return drm_gem_cma_dumb_create_internal(file, dev, args);
+}
+
+static void rcar_du_vdrm_crtc_flush(struct drm_crtc *crtc)
+{
+ struct rcar_du_crtc *rcrtc = to_rcar_crtc(crtc);
+
+ rcar_du_vsp_atomic_flush(rcrtc);
+}
+
+static struct vdrm_funcs vdrm_funcs = {
+ .dumb_create = rcar_du_vdrm_dumb_create,
+ .crtc_flush = rcar_du_vdrm_crtc_flush,
+};
+
+void rcar_du_vdrm_crtc_complete(struct rcar_du_crtc *crtc, unsigned int status)
+{
+ struct rcar_du_vdrm_display *disp;
+
+ list_for_each_entry(disp, &crtc->vdrm_displays, head) {
+ vdrm_drv_handle_vblank(disp->display);
+ if (status & VSP1_DU_STATUS_COMPLETE)
+ vdrm_drv_finish_page_flip(disp->display);
+ }
+}
+
+int rcar_du_vdrm_count(struct rcar_du_device *rcdu)
+{
+ const struct device_node *np = rcdu->dev->of_node;
+ int num;
+
+ num = of_property_count_u32_elems(np, "vdrms");
+ if (num < 0)
+ return 0;
+
+ return num;
+}
+
+int rcar_du_vdrms_init(struct rcar_du_device *rcdu)
+{
+ struct vdrm_device *vdrm;
+ int num_vdrms;
+ int i, ret;
+
+ num_vdrms = rcar_du_vdrm_count(rcdu);
+ if (num_vdrms == 0)
+ return 0;
+
+ rcdu->vdrms = kcalloc(num_vdrms, sizeof(vdrm), GFP_KERNEL);
+ if (!rcdu->vdrms)
+ return -1;
+
+ DRM_INFO("VDRM: num vdrm = %d\n", num_vdrms);
+
+ for (i = 0; i < num_vdrms; i++) {
+ struct of_phandle_args args;
+ const struct device_node *np = rcdu->dev->of_node;
+
+ ret = of_parse_phandle_with_fixed_args(np, "vdrms", 0, i,
+ &args);
+ if (ret < 0) {
+ DRM_WARN("VDRM: failed get vdrm%d.\n", i);
+ goto err;
+ }
+
+ vdrm = vdrm_drv_init(&rcdu->ddev, args.np, 0, NULL,
+ &vdrm_funcs);
+ of_node_put(args.np);
+ if (IS_ERR(vdrm)) {
+ ret = PTR_ERR(vdrm);
+ goto err;
+ }
+
+ rcdu->vdrms[i] = vdrm;
+ rcdu->num_vdrms++;
+ }
+
+ return 0;
+
+err:
+ rcar_du_vdrms_fini(rcdu);
+ rcdu->num_vdrms = 0;
+ return ret;
+}
+
+int rcar_du_vdrm_plane_init(struct vdrm_device *vdrm,
+ struct rcar_du_vsp_plane *plane,
+ const struct drm_plane_funcs *funcs,
+ const struct drm_plane_helper_funcs *helper_funcs,
+ const u32 *formats, unsigned int num_formats,
+ int max_zpos)
+{
+ return vdrm_drv_plane_init(vdrm, &plane->plane, funcs,
+ helper_funcs, formats, num_formats,
+ max_zpos);
+}
+
+int rcar_du_vdrm_crtc_init(struct rcar_du_crtc *crtc, int index)
+{
+ struct rcar_du_device *rcdu;
+ int i;
+
+ rcdu = crtc->dev;
+ for (i = 0; i < rcdu->num_vdrms; i++) {
+ struct vdrm_display *vdisplay;
+ int plane_index = crtc->vsp->num_planes + i;
+ struct drm_plane *plane =
+ &crtc->vsp->planes[plane_index].plane;
+
+ vdisplay = vdrm_drv_display_init(rcdu->vdrms[i], &crtc->crtc,
+ plane);
+ if (IS_ERR(vdisplay))
+ return PTR_ERR(vdisplay);
+
+ rcar_du_crtc_add_vdrm_display(crtc, vdisplay);
+ }
+
+ return 0;
+}
+
+int rcar_du_vdrms_register(struct rcar_du_device *rcdu)
+{
+ int i, ret;
+
+ for (i = 0; i < rcdu->num_vdrms; i++) {
+ ret = vdrm_drv_register(rcdu->vdrms[i]);
+ if (ret)
+ return ret;
+ }
+
+ return 0;
+}
+
+void rcar_du_vdrms_fini(struct rcar_du_device *rcdu)
+{
+ int i;
+
+ for (i = 0; i < rcdu->num_vdrms; i++) {
+ if (rcdu->vdrms[i])
+ vdrm_drv_fini(rcdu->vdrms[i]);
+ }
+
+ for (i = 0; i < RCAR_DU_MAX_CRTCS; i++)
+ rcar_du_crtc_remove_vdrm_displays(&rcdu->crtcs[i]);
+
+ kfree(rcdu->vdrms);
+}
diff --git a/drivers/gpu/drm/rcar-du/rcar_du_vdrm.h b/drivers/gpu/drm/rcar-du/rcar_du_vdrm.h
new file mode 100644
index 000000000000..b12706ceee54
--- /dev/null
+++ b/drivers/gpu/drm/rcar-du/rcar_du_vdrm.h
@@ -0,0 +1,67 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * rcar_du_vdrm.h -- R-Car Display Unit Virtual DRMs
+ *
+ * Copyright (C) 2021 Renesas Electronics Corporation
+ */
+
+#ifndef __RCAR_DU_VDRM_H__
+#define __RCAR_DU_VDRM_H__
+
+#include <drm/drm_atomic.h>
+
+#include "rcar_du_drv.h"
+#include "../vdrm/vdrm_api.h"
+
+#ifdef CONFIG_DRM_RCAR_DU_VDRM
+
+void rcar_du_vdrm_crtc_complete(struct rcar_du_crtc *crtc, unsigned int status);
+void rcar_du_vdrm_vblank_event(struct rcar_du_crtc *crtc);
+int rcar_du_vdrm_count(struct rcar_du_device *rcdu);
+int rcar_du_vdrms_init(struct rcar_du_device *rcdu);
+int rcar_du_vdrm_plane_init(struct vdrm_device *vdrm,
+ struct rcar_du_vsp_plane *plane,
+ const struct drm_plane_funcs *funcs,
+ const struct drm_plane_helper_funcs *helper_funcs,
+ const u32 *formats, unsigned int num_formats,
+ int max_zpos);
+int rcar_du_vdrm_crtc_init(struct rcar_du_crtc *crtc, int index);
+int rcar_du_vdrms_register(struct rcar_du_device *rcdu);
+void rcar_du_vdrms_fini(struct rcar_du_device *rcdu);
+
+#else
+
+static inline void
+rcar_du_vdrm_crtc_complete(struct rcar_du_crtc *crtc, unsigned int status) { }
+static inline void rcar_du_vdrm_vblank_event(struct rcar_du_crtc *crtc) { }
+static inline int rcar_du_vdrm_count(struct rcar_du_device *rcdu)
+{
+ return 0;
+}
+static inline int rcar_du_vdrms_init(struct rcar_du_device *rcdu)
+{
+ return 0;
+}
+static inline int
+rcar_du_vdrm_plane_init(struct vdrm_device *vdrm,
+ struct rcar_du_vsp_plane *plane,
+ const struct drm_plane_funcs *funcs,
+ const struct drm_plane_helper_funcs *helper_funcs,
+ const u32 *formats, unsigned int num_formats,
+ int max_zpos)
+{
+ return 0;
+}
+static inline int rcar_du_vdrm_crtc_init(struct rcar_du_crtc *crtc, int index)
+{
+ return 0;
+}
+static inline int rcar_du_vdrms_register(struct rcar_du_device *rcdu)
+{
+ return 0;
+}
+static inline void rcar_du_vdrms_fini(struct rcar_du_device *rcdu) { }
+
+#endif
+
+#endif /* __RCAR_DU_VDRM_H__ */
diff --git a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
index 23e41c83c875..7666441f0005 100644
--- a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
+++ b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
@@ -31,6 +31,7 @@
#include "rcar_du_kms.h"
#include "rcar_du_vsp.h"
#include "rcar_du_writeback.h"
+#include "rcar_du_vdrm.h"

static void rcar_du_vsp_complete(void *private, unsigned int status, u32 crc)
{
@@ -45,6 +46,8 @@ static void rcar_du_vsp_complete(void *private, unsigned int status, u32 crc)
rcar_du_writeback_complete(crtc);

drm_crtc_add_crc_entry(&crtc->crtc, false, 0, &crc);
+
+ rcar_du_vdrm_crtc_complete(crtc, status);
}

void rcar_du_vsp_enable(struct rcar_du_crtc *crtc)
@@ -373,6 +376,8 @@ int rcar_du_vsp_init(struct rcar_du_vsp *vsp, struct device_node *np,
unsigned int num_planes;
unsigned int i;
int ret;
+ int num_vdrms;
+ int vdrm_index = 0;

/* Find the VSP device and initialize it. */
pdev = of_find_device_by_node(np);
@@ -395,6 +400,8 @@ int rcar_du_vsp_init(struct rcar_du_vsp *vsp, struct device_node *np,
*/
num_planes = rcdu->info->gen >= 3 ? 5 : 4;

+ num_vdrms = rcar_du_vdrm_count(rcdu);
+
vsp->planes = kcalloc(num_planes, sizeof(*vsp->planes), GFP_KERNEL);
if (!vsp->planes)
return -ENOMEM;
@@ -408,6 +415,21 @@ int rcar_du_vsp_init(struct rcar_du_vsp *vsp, struct device_node *np,
plane->vsp = vsp;
plane->index = i;

+ if (i >= num_planes - num_vdrms) {
+ ret = rcar_du_vdrm_plane_init(rcdu->vdrms[vdrm_index],
+ plane,
+ &rcar_du_vsp_plane_funcs,
+ &rcar_du_vsp_plane_helper_funcs,
+ rcar_du_vsp_formats,
+ ARRAY_SIZE(rcar_du_vsp_formats),
+ num_planes - 1);
+ if (ret < 0)
+ return ret;
+
+ vdrm_index++;
+ continue;
+ }
+
ret = drm_universal_plane_init(&rcdu->ddev, &plane->plane,
crtcs, &rcar_du_vsp_plane_funcs,
rcar_du_vsp_formats,
diff --git a/drivers/gpu/drm/rcar-du/rcar_du_vsp.h b/drivers/gpu/drm/rcar-du/rcar_du_vsp.h
index 9b4724159378..0209def9fa6f 100644
--- a/drivers/gpu/drm/rcar-du/rcar_du_vsp.h
+++ b/drivers/gpu/drm/rcar-du/rcar_du_vsp.h
@@ -16,6 +16,7 @@ struct drm_framebuffer;
struct rcar_du_format_info;
struct rcar_du_vsp;
struct sg_table;
+struct vdrm_display;

struct rcar_du_vsp_plane {
struct drm_plane plane;
--
2.25.1

2021-06-21 07:11:57

by Thomas Zimmermann

[permalink] [raw]

Subject: Re: [PATH 0/4] [RFC] Support virtual DRM

Hi

Am 21.06.21 um 08:27 schrieb Tomohito Esaki:
> Virtual DRM splits the overlay planes of a display controller into multiple
> virtual devices to allow each plane to be accessed by each process.
>
> This makes it possible to overlay images output from multiple processes on a
> display. For example, one process displays the camera image without compositor
> while another process overlays the UI.

I briefly looked over your patches. I didn't understand how this is
different to the functionality of a compositor? Shouldn't this be solved
in userspace?

Best regards
Thomas

>
> Virtual DRM driver doesn’t directly control the display hardware and has no
> access to the physical bus. Instead, the virtual DRM driver issues requests to
> the standard DRM device driver (parent) when the hardware needs to be
> controlled. The parent is modified to notify the virtual DRM driver of
> interruptevents from the display hardware. Therefore, in order to use virtual
> DRM, each DRM device driver needs to add code to support virutal DRM.
>
> The only driver supported in this patch series is rcar-du. This patch series
> is divided into multiple. The first patch adds vDRM feature to DRM, and the
> second patch support vDRM for the rcar-du driver. The other patches add
> documentation.
>
> In particular, I would appreciate your advice on the following points:
> * virtual DRM generalization
> I've only tested with rcar-du, is there anything I should consider to make
> virtual DRM work with other drivers?
>
> * Integration to upstream
> I think it is a good idea to add virtual DRM to the DRM core functionality,
> but I would appreciate any suggestions on what needs to be improved for
> integration to upstream.
>
> * dumb_create and fb_create callback
> I think that the dumb_create and fb_create callbacks need to be done by the
> parent, and it is preferable to use the parent's callbacks as they are.
> However, since the dumb buffer needs to be registered in the parent and
> the fb handle needs to be registered in the drm_file of the vDRM, the
> dumb_create callbacks from the parent driver cannot be used as is.
> Therefore, the current implementation of the dumb_create callback is
> workarround.
> What do you think is the best way to deal with this issue?
>
>
> Tomohito Esaki (4):
> Add Virtual DRM device driver
> rcar-du: Add support virtual DRM device
> dt-bindings: display: Add virtual DRM
> doc-rst: Add virtual DRM documentation
>
> .../devicetree/bindings/display/vdrm.yaml | 67 ++
> Documentation/gpu/drivers.rst | 1 +
> Documentation/gpu/vdrm.rst | 51 ++
> drivers/gpu/drm/Kconfig | 7 +
> drivers/gpu/drm/Makefile | 1 +
> drivers/gpu/drm/rcar-du/Kconfig | 4 +
> drivers/gpu/drm/rcar-du/Makefile | 1 +
> drivers/gpu/drm/rcar-du/rcar_du_crtc.c | 42 +
> drivers/gpu/drm/rcar-du/rcar_du_crtc.h | 13 +
> drivers/gpu/drm/rcar-du/rcar_du_drv.c | 13 +
> drivers/gpu/drm/rcar-du/rcar_du_drv.h | 3 +
> drivers/gpu/drm/rcar-du/rcar_du_vdrm.c | 191 ++++
> drivers/gpu/drm/rcar-du/rcar_du_vdrm.h | 67 ++
> drivers/gpu/drm/rcar-du/rcar_du_vsp.c | 22 +
> drivers/gpu/drm/rcar-du/rcar_du_vsp.h | 1 +
> drivers/gpu/drm/vdrm/vdrm_api.h | 68 ++
> drivers/gpu/drm/vdrm/vdrm_drv.c | 859 ++++++++++++++++++
> drivers/gpu/drm/vdrm/vdrm_drv.h | 80 ++
> 18 files changed, 1491 insertions(+)
> create mode 100644 Documentation/devicetree/bindings/display/vdrm.yaml
> create mode 100644 Documentation/gpu/vdrm.rst
> create mode 100644 drivers/gpu/drm/rcar-du/rcar_du_vdrm.c
> create mode 100644 drivers/gpu/drm/rcar-du/rcar_du_vdrm.h
> create mode 100644 drivers/gpu/drm/vdrm/vdrm_api.h
> create mode 100644 drivers/gpu/drm/vdrm/vdrm_drv.c
> create mode 100644 drivers/gpu/drm/vdrm/vdrm_drv.h
>

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer

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2021-06-21 09:26:20

by Maxime Ripard

[permalink] [raw]

Subject: Re: [PATH 0/4] [RFC] Support virtual DRM

Hi,

On Mon, Jun 21, 2021 at 09:10:19AM +0200, Thomas Zimmermann wrote:
> Am 21.06.21 um 08:27 schrieb Tomohito Esaki:
> > Virtual DRM splits the overlay planes of a display controller into multiple
> > virtual devices to allow each plane to be accessed by each process.
> >
> > This makes it possible to overlay images output from multiple processes on a
> > display. For example, one process displays the camera image without compositor
> > while another process overlays the UI.
>
> I briefly looked over your patches. I didn't understand how this is
> different to the functionality of a compositor? Shouldn't this be solved in
> userspace?

I think there could be a bunch of use-cases for something that could
"steal" a plane without the compositor knowing.

Something I'd really like to work at some point for example is that the
downstream RaspberryPi display driver has a visual clue when it's
running too hot or is in over-current.

I don't think this is the right solution though. The DT binding makes it
far too static, and if there's a compositor I'd assume it would want to
know about it somehow (at least if it's from the userspace) ?

Maxime

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2021-06-21 16:08:14

[permalink] [raw]

Subject: Re: [PATH 0/4] [RFC] Support virtual DRM

On 21.06.21 08:27, Tomohito Esaki wrote:

Hi,

> Virtual DRM splits the overlay planes of a display controller into multiple
> virtual devices to allow each plane to be accessed by each process.
>
> This makes it possible to overlay images output from multiple processes on a
> display. For example, one process displays the camera image without compositor
> while another process overlays the UI.

Are you attempting to create an simple in-kernel compositor ?

I don't think that's not the way to go, at least not by touching each
single display driver, and not hardcoding the planes in DT.

What's the actual use case you're doing that for ? Why not using some
userland compositor ?

If you really wanna build a kernel compositor, it should be completely
independent of hw drivers. (well, almost - in case of gpus shall be
used, the commands obviously need to be dispatched the actual driver)

--mtx

--
---
Hinweis: unverschlüsselte E-Mails können leicht abgehört und manipuliert
werden ! Für eine vertrauliche Kommunikation senden Sie bitte ihren
GPG/PGP-Schlüssel zu.
---
Enrico Weigelt, metux IT consult
Free software and Linux embedded engineering
[email protected] -- +49-151-27565287

2021-06-22 04:05:32

[permalink] [raw]

Subject: Re: [PATH 0/4] [RFC] Support virtual DRM

Hi, Thomas
Thank you for reply.

On 2021/06/21 16:10, Thomas Zimmermann wrote:
> Hi
>
> Am 21.06.21 um 08:27 schrieb Tomohito Esaki:
>> Virtual DRM splits the overlay planes of a display controller into
>> multiple
>> virtual devices to allow each plane to be accessed by each process.
>>
>> This makes it possible to overlay images output from multiple
>> processes on a
>> display. For example, one process displays the camera image without
>> compositor
>> while another process overlays the UI.
>
> I briefly looked over your patches. I didn't understand how this is
> different to the functionality of a compositor? Shouldn't this be solved
> in userspace?

I think when latency is important (e.g., AR, VR, for displaying camera
images in IVI systems), there may be use cases where the compositor
cannot be used.
Normally, when the image is passed through the compositor, it is
displayed after 2 VSYNC at most, because the compositor combines the
image with VSYNC synchronization. On the other hand, if we use vDRM, the
image will be displayed at the next VSYNC, so it will be displayed after
1 VSYNC at most.

Also, since the compositor is a single point of failure, we may not want
to make it dependent on it.

Best regards
Tomohito Esaki

2021-06-22 04:08:46

[permalink] [raw]

Subject: Re: [PATH 0/4] [RFC] Support virtual DRM

Hi, Enrico Weigelt
Thank you for reply.

On 2021/06/22 1:05, Enrico Weigelt, metux IT consult wrote:
> On 21.06.21 08:27, Tomohito Esaki wrote:
>
> Hi,
>
>> Virtual DRM splits the overlay planes of a display controller into multiple
>> virtual devices to allow each plane to be accessed by each process.
>>
>> This makes it possible to overlay images output from multiple processes on a
>> display. For example, one process displays the camera image without compositor
>> while another process overlays the UI.
>
> Are you attempting to create an simple in-kernel compositor ?

I think the basic idea is the same as DRMlease.
We want to separate the resources from the master in units of planes,
so we proposed virtual DRM.
I think the advantage of vDRM is that you can use general DRM APIs
in userland.

> I don't think that's not the way to go, at least not by touching each
> single display driver, and not hardcoding the planes in DT.

Thank you for comment. I will reconsider about DT.

> What's the actual use case you're doing that for ? Why not using some
> userland compositor ?

I think when latency is important (e.g., AR, VR, for displaying camera
images in IVI systems), there may be use cases where the compositor
cannot be used.
Normally, when the image is passed through the compositor, it is
displayed after 2 VSYNC at most, because the compositor combines the
image with VSYNC synchronization. On the other hand, if we use vDRM, the
image will be displayed at the next VSYNC, so it will be displayed after
1 VSYNC at most.

Also, since the compositor is a single point of failure, we may not want
to make it dependent on it.

Best regards
Tomohito Esaki

2021-06-22 04:38:18

[permalink] [raw]

Subject: Re: [PATH 0/4] [RFC] Support virtual DRM

Hi, Maxime
Thank you for reply.

On 2021/06/21 18:24, Maxime Ripard wrote:
> Hi,
>
> On Mon, Jun 21, 2021 at 09:10:19AM +0200, Thomas Zimmermann wrote:
>> Am 21.06.21 um 08:27 schrieb Tomohito Esaki:
>>> Virtual DRM splits the overlay planes of a display controller into multiple
>>> virtual devices to allow each plane to be accessed by each process.
>>>
>>> This makes it possible to overlay images output from multiple processes on a
>>> display. For example, one process displays the camera image without compositor
>>> while another process overlays the UI.
>>
>> I briefly looked over your patches. I didn't understand how this is
>> different to the functionality of a compositor? Shouldn't this be solved in
>> userspace?
>
> I think there could be a bunch of use-cases for something that could
> "steal" a plane without the compositor knowing.
>
> Something I'd really like to work at some point for example is that the
> downstream RaspberryPi display driver has a visual clue when it's
> running too hot or is in over-current.
>
> I don't think this is the right solution though. The DT binding makes it
> far too static, and if there's a compositor I'd assume it would want to
> know about it somehow (at least if it's from the userspace) ?
>

I will reconsider the DT bindings.

We want to separate the resources from the master in units of planes,
so we proposed virtual DRM.
By separating the plane from the master and making it appear as
a virtual DRM devicein userland, the plane can be accessed from
userland using the general DRM API.
What do you think about this idea?

Best Regards
Tomohito Esaki

2021-06-22 07:59:49

[permalink] [raw]

Subject: Re: [PATH 0/4] [RFC] Support virtual DRM

On Tue, 22 Jun 2021 13:02:59 +0900
Esaki Tomohito <[email protected]> wrote:

> Hi, Thomas
> Thank you for reply.
>
> On 2021/06/21 16:10, Thomas Zimmermann wrote:
> > Hi
> >
> > Am 21.06.21 um 08:27 schrieb Tomohito Esaki:
> >> Virtual DRM splits the overlay planes of a display controller into
> >> multiple
> >> virtual devices to allow each plane to be accessed by each process.
> >>
> >> This makes it possible to overlay images output from multiple
> >> processes on a
> >> display. For example, one process displays the camera image without
> >> compositor
> >> while another process overlays the UI.
> >
> > I briefly looked over your patches. I didn't understand how this is
> > different to the functionality of a compositor? Shouldn't this be solved
> > in userspace?
>
> I think when latency is important (e.g., AR, VR, for displaying camera
> images in IVI systems), there may be use cases where the compositor
> cannot be used.

Hi,

> Normally, when the image is passed through the compositor, it is
> displayed after 2 VSYNC at most, because the compositor combines the
> image with VSYNC synchronization.

This is not a universal fact. You can write a Wayland compositor that
consistently reaches app-to-screen latency of less than one monitor
refresh cycle, while also using KMS planes.

I believe Weston succeeds in this already if you write the Wayland
application accordingly.

Thanks,
pq

Attachments:

2021-06-22 08:14:06

[permalink] [raw]

Subject: Re: [PATH 0/4] [RFC] Support virtual DRM

On Tue, 22 Jun 2021 13:03:39 +0900
Esaki Tomohito <[email protected]> wrote:

> Hi, Enrico Weigelt
> Thank you for reply.
>
> On 2021/06/22 1:05, Enrico Weigelt, metux IT consult wrote:
> > On 21.06.21 08:27, Tomohito Esaki wrote:
> >
> > Hi,
> >
> >> Virtual DRM splits the overlay planes of a display controller into multiple
> >> virtual devices to allow each plane to be accessed by each process.
> >>
> >> This makes it possible to overlay images output from multiple processes on a
> >> display. For example, one process displays the camera image without compositor
> >> while another process overlays the UI.
> >
> > Are you attempting to create an simple in-kernel compositor ?
>
> I think the basic idea is the same as DRMlease.

Hi,

indeed. Why not use DRM leases instead?

> We want to separate the resources from the master in units of planes,
> so we proposed virtual DRM.
> I think the advantage of vDRM is that you can use general DRM APIs
> in userland.

You do that with DRM leases too.

> > I don't think that's not the way to go, at least not by touching each
> > single display driver, and not hardcoding the planes in DT.
>
> Thank you for comment. I will reconsider about DT.
>
> > What's the actual use case you're doing that for ? Why not using some
> > userland compositor ?
>
> I think when latency is important (e.g., AR, VR, for displaying camera
> images in IVI systems), there may be use cases where the compositor
> cannot be used.
> Normally, when the image is passed through the compositor, it is
> displayed after 2 VSYNC at most, because the compositor combines the
> image with VSYNC synchronization. On the other hand, if we use vDRM, the
> image will be displayed at the next VSYNC, so it will be displayed after
> 1 VSYNC at most.

As I said in my other email, this is false in the general sense.

> Also, since the compositor is a single point of failure, we may not want
> to make it dependent on it.

This... I'm not quite sure I buy it. If any of all the programs using
virtual KMS crashes, you still lose some crucial components from your
display. Maybe that program, while crashing, uploads such a bad state
to its very own KMS plane, that it causes other KMS planes to
malfunction. Then you need to detect this situation and still restart
everything, not just the crashed program.

I would think a userspace compositor approach is actually more
reliable. You write the compositor to be extremely robust. Exactly
because the compositor is in control of the complete display device and
not just little pieces of it, it can see what is happening and it can
mitigate problems. If you have more unreliable components needing
access to display, make those clients to the compositor, so they can
crash and malfunction on their own without potentially killing the
whole display device. If you are as concerned about latency as XR
people are, then use DRM leases.

Also, what if your virtual KMS driver has a bug? Restarting the kernel
is much harder that restarting a userspace compositor that hands out
DRM leases.

The userspace compositor could even be such that it does nothing more
than handing out DRM leases. However, DRM leases have the problem that
there is no single entity responsible for keeping the display device
working, but that responsibility is split between several processes and
none of them sees the whole picture.

Btw. VKMS is an existing DRM driver, so your name choice is conflicting.

Thanks,
pq

Attachments:

2021-06-22 09:15:15

by Thomas Zimmermann

[permalink] [raw]

Subject: Re: [PATH 0/4] [RFC] Support virtual DRM

Hi

Am 22.06.21 um 06:02 schrieb Esaki Tomohito:
> Hi, Thomas
> Thank you for reply.
>
> On 2021/06/21 16:10, Thomas Zimmermann wrote:
>> Hi
>>
>> Am 21.06.21 um 08:27 schrieb Tomohito Esaki:
>>> Virtual DRM splits the overlay planes of a display controller into
>>> multiple
>>> virtual devices to allow each plane to be accessed by each process.
>>>
>>> This makes it possible to overlay images output from multiple
>>> processes on a
>>> display. For example, one process displays the camera image without
>>> compositor
>>> while another process overlays the UI.
>>
>> I briefly looked over your patches. I didn't understand how this is
>> different to the functionality of a compositor? Shouldn't this be solved
>> in userspace?
>
> I think when latency is important (e.g., AR, VR, for displaying camera
> images in IVI systems), there may be use cases where the compositor
> cannot be used.
> Normally, when the image is passed through the compositor, it is
> displayed after 2 VSYNC at most, because the compositor combines the
> image with VSYNC synchronization. On the other hand, if we use vDRM, the
> image will be displayed at the next VSYNC, so it will be displayed after
> 1 VSYNC at most.

Other commenters already addressed these points.

>
> Also, since the compositor is a single point of failure, we may not want
> to make it dependent on it.

The kernel is also a single point of failure.

TBH I don't think this feature should be merged until there's a clear
use case that cannot be solved in userspace idiomatically.

Best regards
Thomas

>
> Best regards
> Tomohito Esaki
>

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer

Attachments:

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2021-06-22 19:14:14

by Daniel Vetter

[permalink] [raw]

Subject: Re: [PATH 0/4] [RFC] Support virtual DRM

On Tue, Jun 22, 2021 at 10:12 AM Pekka Paalanen <[email protected]> wrote:
>
> On Tue, 22 Jun 2021 13:03:39 +0900
> Esaki Tomohito <[email protected]> wrote:
>
> > Hi, Enrico Weigelt
> > Thank you for reply.
> >
> > On 2021/06/22 1:05, Enrico Weigelt, metux IT consult wrote:
> > > On 21.06.21 08:27, Tomohito Esaki wrote:
> > >
> > > Hi,
> > >
> > >> Virtual DRM splits the overlay planes of a display controller into multiple
> > >> virtual devices to allow each plane to be accessed by each process.
> > >>
> > >> This makes it possible to overlay images output from multiple processes on a
> > >> display. For example, one process displays the camera image without compositor
> > >> while another process overlays the UI.
> > >
> > > Are you attempting to create an simple in-kernel compositor ?
> >
> > I think the basic idea is the same as DRMlease.
>
> Hi,
>
> indeed. Why not use DRM leases instead?
>
> > We want to separate the resources from the master in units of planes,
> > so we proposed virtual DRM.
> > I think the advantage of vDRM is that you can use general DRM APIs
> > in userland.
>
> You do that with DRM leases too.
>
> > > I don't think that's not the way to go, at least not by touching each
> > > single display driver, and not hardcoding the planes in DT.
> >
> > Thank you for comment. I will reconsider about DT.
> >
> > > What's the actual use case you're doing that for ? Why not using some
> > > userland compositor ?
> >
> > I think when latency is important (e.g., AR, VR, for displaying camera
> > images in IVI systems), there may be use cases where the compositor
> > cannot be used.
> > Normally, when the image is passed through the compositor, it is
> > displayed after 2 VSYNC at most, because the compositor combines the
> > image with VSYNC synchronization. On the other hand, if we use vDRM, the
> > image will be displayed at the next VSYNC, so it will be displayed after
> > 1 VSYNC at most.
>
> As I said in my other email, this is false in the general sense.
>
> > Also, since the compositor is a single point of failure, we may not want
> > to make it dependent on it.
>
> This... I'm not quite sure I buy it. If any of all the programs using
> virtual KMS crashes, you still lose some crucial components from your
> display. Maybe that program, while crashing, uploads such a bad state
> to its very own KMS plane, that it causes other KMS planes to
> malfunction. Then you need to detect this situation and still restart
> everything, not just the crashed program.

This, a hundred times. At least in general it's impossible to
guarantee resource isolation between different parts of a kms device -
everything is shared at least in some driver in funny ways.

The only thing we try to guarantee is that if you keep flipping the
same plane with same pixel format, stride, offset, absolutely
everything except the memory block unchanged, then that's guaranteed
to work. Everything else is off the table.

This is why the drm-lease design ended up with revoke support, because
if something goes wrong a superior instance (the compositor, the
kernel can't decide that for userspace) needs to decide whom to shoot
and revoke their access.

> I would think a userspace compositor approach is actually more
> reliable. You write the compositor to be extremely robust. Exactly
> because the compositor is in control of the complete display device and
> not just little pieces of it, it can see what is happening and it can
> mitigate problems. If you have more unreliable components needing
> access to display, make those clients to the compositor, so they can
> crash and malfunction on their own without potentially killing the
> whole display device. If you are as concerned about latency as XR
> people are, then use DRM leases.
>
> Also, what if your virtual KMS driver has a bug? Restarting the kernel
> is much harder that restarting a userspace compositor that hands out
> DRM leases.
>
> The userspace compositor could even be such that it does nothing more
> than handing out DRM leases. However, DRM leases have the problem that
> there is no single entity responsible for keeping the display device
> working, but that responsibility is split between several processes and
> none of them sees the whole picture.

Yeah I think a compositor for this use-case, written in Rust and
heavily audited/proofed is probably a lot more reliable than cobbling
ill-defined kernel driver code on top of barely-defined hw semantics
in resource-sharing cases.

> Btw. VKMS is an existing DRM driver, so your name choice is conflicting.

Yeah that too :-)
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

2021-06-23 06:57:34

[permalink] [raw]

Subject: Re: [PATH 0/4] [RFC] Support virtual DRM

Hi,
Thank you all for your comments.

On 2021/06/22 17:12, Pekka Paalanen wrote:
> On Tue, 22 Jun 2021 13:03:39 +0900
> Esaki Tomohito <[email protected]> wrote:
>
>> Hi, Enrico Weigelt
>> Thank you for reply.
>>
>> On 2021/06/22 1:05, Enrico Weigelt, metux IT consult wrote:
>>> On 21.06.21 08:27, Tomohito Esaki wrote:
>>>
>>> Hi,
>>>
>>>> Virtual DRM splits the overlay planes of a display controller into multiple
>>>> virtual devices to allow each plane to be accessed by each process.
>>>>
>>>> This makes it possible to overlay images output from multiple processes on a
>>>> display. For example, one process displays the camera image without compositor
>>>> while another process overlays the UI.
>>>
>>> Are you attempting to create an simple in-kernel compositor ?
>>
>> I think the basic idea is the same as DRMlease.
>
> Hi,
>
> indeed. Why not use DRM leases instead?
>

In this use case, I understand that this is not possible with DRM lease,
am I wrong?
I understand that it?s not possible to lease a plane and update planes
on the same output independently from different processes in current DRM
lease.

If this is correct, what do you think of adding support for plane leases
to the DRM lease to handle this case?

Thanks,
Tomohito Esaki

2021-06-23 08:16:30

by Michel Dänzer

[permalink] [raw]

Subject: Re: [PATH 0/4] [RFC] Support virtual DRM

On 2021-06-22 9:57 a.m., Pekka Paalanen wrote:
> On Tue, 22 Jun 2021 13:02:59 +0900
> Esaki Tomohito <[email protected]> wrote:
>
>> Hi, Thomas
>> Thank you for reply.
>>
>> On 2021/06/21 16:10, Thomas Zimmermann wrote:
>>> Hi
>>>
>>> Am 21.06.21 um 08:27 schrieb Tomohito Esaki:
>>>> Virtual DRM splits the overlay planes of a display controller into
>>>> multiple
>>>> virtual devices to allow each plane to be accessed by each process.
>>>>
>>>> This makes it possible to overlay images output from multiple
>>>> processes on a
>>>> display. For example, one process displays the camera image without
>>>> compositor
>>>> while another process overlays the UI.
>>>
>>> I briefly looked over your patches. I didn't understand how this is
>>> different to the functionality of a compositor? Shouldn't this be solved
>>> in userspace?
>>
>> I think when latency is important (e.g., AR, VR, for displaying camera
>> images in IVI systems), there may be use cases where the compositor
>> cannot be used.
>
> Hi,
>
>> Normally, when the image is passed through the compositor, it is
>> displayed after 2 VSYNC at most, because the compositor combines the
>> image with VSYNC synchronization.
>
> This is not a universal fact. You can write a Wayland compositor that
> consistently reaches app-to-screen latency of less than one monitor
> refresh cycle, while also using KMS planes.
>
> I believe Weston succeeds in this already if you write the Wayland
> application accordingly.

For a specific example, https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1620 allows app-to-screen latency as low as ~6 ms (including a fixed 2 ms buffer to avoid skipped frames). mutter doesn't use KMS planes yet, but if anything I'd expect that to help rather than hurt for latency (if the compositor doesn't need to draw anything).

--
Earthling Michel Dänzer | https://redhat.com
Libre software enthusiast | Mesa and X developer

2021-06-23 08:22:45

[permalink] [raw]

Subject: Re: [PATH 0/4] [RFC] Support virtual DRM

On 2021/06/23 17:04, Michel Dänzer wrote:
> On 2021-06-22 9:57 a.m., Pekka Paalanen wrote:
>> On Tue, 22 Jun 2021 13:02:59 +0900
>> Esaki Tomohito <[email protected]> wrote:
>>
>>> Hi, Thomas
>>> Thank you for reply.
>>>
>>> On 2021/06/21 16:10, Thomas Zimmermann wrote:
>>>> Hi
>>>>
>>>> Am 21.06.21 um 08:27 schrieb Tomohito Esaki:
>>>>> Virtual DRM splits the overlay planes of a display controller into
>>>>> multiple
>>>>> virtual devices to allow each plane to be accessed by each process.
>>>>>
>>>>> This makes it possible to overlay images output from multiple
>>>>> processes on a
>>>>> display. For example, one process displays the camera image without
>>>>> compositor
>>>>> while another process overlays the UI.
>>>>
>>>> I briefly looked over your patches. I didn't understand how this is
>>>> different to the functionality of a compositor? Shouldn't this be solved
>>>> in userspace?
>>>
>>> I think when latency is important (e.g., AR, VR, for displaying camera
>>> images in IVI systems), there may be use cases where the compositor
>>> cannot be used.
>>
>> Hi,
>>
>>> Normally, when the image is passed through the compositor, it is
>>> displayed after 2 VSYNC at most, because the compositor combines the
>>> image with VSYNC synchronization.
>>
>> This is not a universal fact. You can write a Wayland compositor that
>> consistently reaches app-to-screen latency of less than one monitor
>> refresh cycle, while also using KMS planes.
>>
>> I believe Weston succeeds in this already if you write the Wayland
>> application accordingly.
>
> For a specific example, https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1620 allows app-to-screen latency as low as ~6 ms (including a fixed 2 ms buffer to avoid skipped frames). mutter doesn't use KMS planes yet, but if anything I'd expect that to help rather than hurt for latency (if the compositor doesn't need to draw anything).

Thank you for providing specific examples.

Best regards
Esaki

2021-06-23 08:40:18

[permalink] [raw]

Subject: Re: [PATH 0/4] [RFC] Support virtual DRM

On Wed, 23 Jun 2021 15:56:05 +0900
Esaki Tomohito <[email protected]> wrote:

> Hi,
> Thank you all for your comments.
>
> On 2021/06/22 17:12, Pekka Paalanen wrote:
> > On Tue, 22 Jun 2021 13:03:39 +0900
> > Esaki Tomohito <[email protected]> wrote:
> >
> >> Hi, Enrico Weigelt
> >> Thank you for reply.
> >>
> >> On 2021/06/22 1:05, Enrico Weigelt, metux IT consult wrote:
> >>> On 21.06.21 08:27, Tomohito Esaki wrote:
> >>>
> >>> Hi,
> >>>
> >>>> Virtual DRM splits the overlay planes of a display controller into multiple
> >>>> virtual devices to allow each plane to be accessed by each process.
> >>>>
> >>>> This makes it possible to overlay images output from multiple processes on a
> >>>> display. For example, one process displays the camera image without compositor
> >>>> while another process overlays the UI.
> >>>
> >>> Are you attempting to create an simple in-kernel compositor ?
> >>
> >> I think the basic idea is the same as DRMlease.
> >
> > Hi,
> >
> > indeed. Why not use DRM leases instead?
> >
>
> In this use case, I understand that this is not possible with DRM lease,
> am I wrong?
> I understand that it’s not possible to lease a plane and update planes
> on the same output independently from different processes in current DRM
> lease.
>
> If this is correct, what do you think of adding support for plane leases
> to the DRM lease to handle this case?

Hi,

I would love to see support added for leasing individual planes,
especially to replace the virtual DRM proposal which seems to be
eradicating everything that atomic modesetting and nuclear pageflip
have built over the many years.

However, please note that "on the same output independently" is
physically impossible. Semantically, the planes define what a CRTC
scans out, and the CRTC defines the scanout timings. Therefore it is not
possible to update individual planes independently, they will all
always share the timings of the CRTC.

That combined with KMS not allowing multiple updates to be queued at
the same time for the same CRTC (atomic commits and legacy pageflips
returning EBUSY) makes the plane updates very much inter-dependent.

If you want to avoid EBUSY and have planes update on the vblank you
intended, you really need a userspace compositor to pull everything
together *before* submitting anything to the kernel.

Thanks,
pq

Attachments:

2021-06-23 09:23:44

[permalink] [raw]

Subject: Re: [PATH 0/4] [RFC] Support virtual DRM

On 2021/06/23 17:39, Pekka Paalanen wrote:
> On Wed, 23 Jun 2021 15:56:05 +0900
> Esaki Tomohito <[email protected]> wrote:
>
>> Hi,
>> Thank you all for your comments.
>>
>> On 2021/06/22 17:12, Pekka Paalanen wrote:
>>> On Tue, 22 Jun 2021 13:03:39 +0900
>>> Esaki Tomohito <[email protected]> wrote:
>>>
>>>> Hi, Enrico Weigelt
>>>> Thank you for reply.
>>>>
>>>> On 2021/06/22 1:05, Enrico Weigelt, metux IT consult wrote:
>>>>> On 21.06.21 08:27, Tomohito Esaki wrote:
>>>>>
>>>>> Hi,
>>>>>
>>>>>> Virtual DRM splits the overlay planes of a display controller into multiple
>>>>>> virtual devices to allow each plane to be accessed by each process.
>>>>>>
>>>>>> This makes it possible to overlay images output from multiple processes on a
>>>>>> display. For example, one process displays the camera image without compositor
>>>>>> while another process overlays the UI.
>>>>>
>>>>> Are you attempting to create an simple in-kernel compositor ?
>>>>
>>>> I think the basic idea is the same as DRMlease.
>>>
>>> Hi,
>>>
>>> indeed. Why not use DRM leases instead?
>>>
>>
>> In this use case, I understand that this is not possible with DRM lease,
>> am I wrong?
>> I understand that it’s not possible to lease a plane and update planes
>> on the same output independently from different processes in current DRM
>> lease.
>>
>> If this is correct, what do you think of adding support for plane leases
>> to the DRM lease to handle this case?
>
> Hi,
>
> I would love to see support added for leasing individual planes,
> especially to replace the virtual DRM proposal which seems to be
> eradicating everything that atomic modesetting and nuclear pageflip
> have built over the many years.
>
> However, please note that "on the same output independently" is
> physically impossible. Semantically, the planes define what a CRTC
> scans out, and the CRTC defines the scanout timings. Therefore it is not
> possible to update individual planes independently, they will all
> always share the timings of the CRTC.
>
> That combined with KMS not allowing multiple updates to be queued at
> the same time for the same CRTC (atomic commits and legacy pageflips
> returning EBUSY) makes the plane updates very much inter-dependent.
>
> If you want to avoid EBUSY and have planes update on the vblank you
> intended, you really need a userspace compositor to pull everything
> together *before* submitting anything to the kernel.

Hi,

Thank you for your comments and advice.
I will consider leasing a plane.

Thanks,
Esaki

2021-06-23 11:43:00

[permalink] [raw]

Subject: Re: [PATH 0/4] [RFC] Support virtual DRM

On Wed, 23 Jun 2021 18:22:47 +0900
Esaki Tomohito <[email protected]> wrote:

> On 2021/06/23 17:39, Pekka Paalanen wrote:
> > On Wed, 23 Jun 2021 15:56:05 +0900
> > Esaki Tomohito <[email protected]> wrote:
> >
> >> Hi,
> >> Thank you all for your comments.
> >>
> >> On 2021/06/22 17:12, Pekka Paalanen wrote:
> >>> On Tue, 22 Jun 2021 13:03:39 +0900
> >>> Esaki Tomohito <[email protected]> wrote:
> >>>
> >>>> Hi, Enrico Weigelt
> >>>> Thank you for reply.
> >>>>
> >>>> On 2021/06/22 1:05, Enrico Weigelt, metux IT consult wrote:
> >>>>> On 21.06.21 08:27, Tomohito Esaki wrote:
> >>>>>
> >>>>> Hi,
> >>>>>
> >>>>>> Virtual DRM splits the overlay planes of a display controller into multiple
> >>>>>> virtual devices to allow each plane to be accessed by each process.
> >>>>>>
> >>>>>> This makes it possible to overlay images output from multiple processes on a
> >>>>>> display. For example, one process displays the camera image without compositor
> >>>>>> while another process overlays the UI.
> >>>>>
> >>>>> Are you attempting to create an simple in-kernel compositor ?
> >>>>
> >>>> I think the basic idea is the same as DRMlease.
> >>>
> >>> Hi,
> >>>
> >>> indeed. Why not use DRM leases instead?
> >>>
> >>
> >> In this use case, I understand that this is not possible with DRM lease,
> >> am I wrong?
> >> I understand that it’s not possible to lease a plane and update planes
> >> on the same output independently from different processes in current DRM
> >> lease.
> >>
> >> If this is correct, what do you think of adding support for plane leases
> >> to the DRM lease to handle this case?
> >
> > Hi,
> >
> > I would love to see support added for leasing individual planes,
> > especially to replace the virtual DRM proposal which seems to be
> > eradicating everything that atomic modesetting and nuclear pageflip
> > have built over the many years.
> >
> > However, please note that "on the same output independently" is
> > physically impossible. Semantically, the planes define what a CRTC
> > scans out, and the CRTC defines the scanout timings. Therefore it is not
> > possible to update individual planes independently, they will all
> > always share the timings of the CRTC.
> >
> > That combined with KMS not allowing multiple updates to be queued at
> > the same time for the same CRTC (atomic commits and legacy pageflips
> > returning EBUSY) makes the plane updates very much inter-dependent.
> >
> > If you want to avoid EBUSY and have planes update on the vblank you
> > intended, you really need a userspace compositor to pull everything
> > together *before* submitting anything to the kernel.
>
> Hi,
>
> Thank you for your comments and advice.
> I will consider leasing a plane.

Hi,

I wish you considered a userspace compositor first, once more, with
passion.

It does not need to be Weston, and it does not need to use Wayland.
Just a userspace daemon that owns the whole display device and somehow
talks to whatever else wants stuff on screen.

I have not seen any evidence that leasing individual planes would do
you any good. I can easily see it doing you harm. I'm only saying that
it would be better than the virtual DRM proposal if you absolutely have
to go there. Please, consider not going there at all.

"On the same output independently" is not possible for the very simple
reason that the pixel data needs to be streamed serially to a monitor.

Thanks,
pq

Attachments:

2021-06-23 14:40:35

by Maxime Ripard

[permalink] [raw]

Subject: Re: [PATH 0/4] [RFC] Support virtual DRM

On Tue, Jun 22, 2021 at 01:36:48PM +0900, Esaki Tomohito wrote:
> Hi, Maxime
> Thank you for reply.
>
> On 2021/06/21 18:24, Maxime Ripard wrote:
> > Hi,
> >
> > On Mon, Jun 21, 2021 at 09:10:19AM +0200, Thomas Zimmermann wrote:
> >> Am 21.06.21 um 08:27 schrieb Tomohito Esaki:
> >>> Virtual DRM splits the overlay planes of a display controller into multiple
> >>> virtual devices to allow each plane to be accessed by each process.
> >>>
> >>> This makes it possible to overlay images output from multiple processes on a
> >>> display. For example, one process displays the camera image without compositor
> >>> while another process overlays the UI.
> >>
> >> I briefly looked over your patches. I didn't understand how this is
> >> different to the functionality of a compositor? Shouldn't this be solved in
> >> userspace?
> >
> > I think there could be a bunch of use-cases for something that could
> > "steal" a plane without the compositor knowing.
> >
> > Something I'd really like to work at some point for example is that the
> > downstream RaspberryPi display driver has a visual clue when it's
> > running too hot or is in over-current.
> >
> > I don't think this is the right solution though. The DT binding makes it
> > far too static, and if there's a compositor I'd assume it would want to
> > know about it somehow (at least if it's from the userspace) ?
> >
>
> I will reconsider the DT bindings.
>
> We want to separate the resources from the master in units of planes,
> so we proposed virtual DRM.
> By separating the plane from the master and making it appear as
> a virtual DRM devicein userland, the plane can be accessed from
> userland using the general DRM API.
> What do you think about this idea?

I guess you'd need to detail a bit more what your use case is exactly,
and what issue you're trying to address.

Generally speaking, I'm not really sure how you can separate a KMS
driver from its planes.

Like, assuming that you have that super important application putting
the rear-end camera on the display: I'd assume you want the connector
and bridges to remain enabled? How are you going to synchronize with the
compositor if it wants to disable it, or change resolution?

Similarly, some features exposed on the connector, like bpc, might
affect the input format you want to have for your planes?

Maxime

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2021-06-25 01:57:16