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Date:   Tue, 18 Jun 2019 11:33:56 +0200
From:   Daniel Vetter <daniel@ffwll.ch>
To:     Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Cc:     Brian Starkey <brian.starkey@arm.com>,
        Liviu Dudau <liviu.dudau@arm.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        Haneen Mohammed <hamohammed.sa@gmail.com>,
        Simon Ser <contact@emersion.fr>,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH V2 5/5] drm/vkms: Add support for writeback
Message-ID: <20190618093356.GR12905@phenom.ffwll.local>
Mail-Followup-To: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>,
        Brian Starkey <brian.starkey@arm.com>,
        Liviu Dudau <liviu.dudau@arm.com>,
        Haneen Mohammed <hamohammed.sa@gmail.com>,
        Simon Ser <contact@emersion.fr>, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org
References: <cover.1560820888.git.rodrigosiqueiramelo@gmail.com>
 <4787369d4927fa709da050e7481e48102842fd97.1560820888.git.rodrigosiqueiramelo@gmail.com>
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On Mon, Jun 17, 2019 at 11:45:55PM -0300, Rodrigo Siqueira wrote:
> This patch implements the necessary functions to add writeback support
> for vkms. This feature is useful for testing compositors if you don't
> have hardware with writeback support.
> 
> Change in V2:
> - Rework signal completion (Brian)
> - Integrates writeback with active_planes (Daniel)
> - Compose cursor (Daniel)

Not quite what I had in mind ... my idea was to reuse the crc worker
(hence renaming all that stuff to vkms_composer). The problem here is that
now we have the blend/compose code duplicated, at least parts of it. Plus
if you enable both crc and writeback, then we compose 2x, which is a bit
too much.

Rough sketch of an implementation:

- add writeback_pending, like we have crc_pending already. Difference is
  that writeback is one-shot, i.e. set it in atomic_check somewhere, clear
  it in the crc_worker (well, composer_worker now). vblank hrtimer will
  not re-enable that one (unlike crc_pending).

- in the crc worker, if writeback_pending is set, then compose everything
  into the writeback buffer instead of into our private crc buffer. Except
  that we use different memory, crc computation will be done exactly the
  same. For subsequent frames with the same crtc_state we will again use
  the normal crc buffer to compose & compute the crc.

The benefit here is that we'll only have one place in vkms that does
composing, so if we add lots more features in the future, it'll be much
easier to maintain. Also since this guarantees that the crc will match
exactly what we've written back, we can use the crc to help validate our
writeback code.

Cheers, Daniel

> 
> Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
> ---
>  drivers/gpu/drm/vkms/Makefile         |   3 +-
>  drivers/gpu/drm/vkms/vkms_drv.c       |   7 ++
>  drivers/gpu/drm/vkms/vkms_drv.h       |   6 +
>  drivers/gpu/drm/vkms/vkms_output.c    |   6 +
>  drivers/gpu/drm/vkms/vkms_writeback.c | 166 ++++++++++++++++++++++++++
>  5 files changed, 187 insertions(+), 1 deletion(-)
>  create mode 100644 drivers/gpu/drm/vkms/vkms_writeback.c
> 
> diff --git a/drivers/gpu/drm/vkms/Makefile b/drivers/gpu/drm/vkms/Makefile
> index b4c040854bd6..091e6fa643d1 100644
> --- a/drivers/gpu/drm/vkms/Makefile
> +++ b/drivers/gpu/drm/vkms/Makefile
> @@ -6,6 +6,7 @@ vkms-y := \
>  	vkms_crtc.o \
>  	vkms_gem.o \
>  	vkms_composer.o \
> -	vkms_crc.o
> +	vkms_crc.o \
> +	vkms_writeback.o
>  
>  obj-$(CONFIG_DRM_VKMS) += vkms.o
> diff --git a/drivers/gpu/drm/vkms/vkms_drv.c b/drivers/gpu/drm/vkms/vkms_drv.c
> index 966b3d653189..d870779abf9d 100644
> --- a/drivers/gpu/drm/vkms/vkms_drv.c
> +++ b/drivers/gpu/drm/vkms/vkms_drv.c
> @@ -30,6 +30,10 @@ bool enable_cursor;
>  module_param_named(enable_cursor, enable_cursor, bool, 0444);
>  MODULE_PARM_DESC(enable_cursor, "Enable/Disable cursor support");
>  
> +bool enable_writeback;
> +module_param_named(enable_writeback, enable_writeback, bool, 0444);
> +MODULE_PARM_DESC(enable_writeback, "Enable/Disable writeback connector");
> +
>  static const struct file_operations vkms_driver_fops = {
>  	.owner		= THIS_MODULE,
>  	.open		= drm_open,
> @@ -158,6 +162,9 @@ static int __init vkms_init(void)
>  		goto out_fini;
>  	}
>  
> +	if (enable_writeback)
> +		DRM_INFO("Writeback connector enabled");
> +
>  	ret = vkms_modeset_init(vkms_device);
>  	if (ret)
>  		goto out_fini;
> diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h
> index ad63dbe5e994..bf3fa737b3d7 100644
> --- a/drivers/gpu/drm/vkms/vkms_drv.h
> +++ b/drivers/gpu/drm/vkms/vkms_drv.h
> @@ -7,6 +7,7 @@
>  #include <drm/drm.h>
>  #include <drm/drm_gem.h>
>  #include <drm/drm_encoder.h>
> +#include <drm/drm_writeback.h>
>  #include <linux/hrtimer.h>
>  
>  #define XRES_MIN    20
> @@ -19,6 +20,7 @@
>  #define YRES_MAX  8192
>  
>  extern bool enable_cursor;
> +extern bool enable_writeback;
>  
>  struct vkms_data {
>  	struct drm_framebuffer fb;
> @@ -63,6 +65,7 @@ struct vkms_output {
>  	struct drm_crtc crtc;
>  	struct drm_encoder encoder;
>  	struct drm_connector connector;
> +	struct drm_writeback_connector wb_connector;
>  	struct hrtimer vblank_hrtimer;
>  	ktime_t period_ns;
>  	struct drm_pending_vblank_event *event;
> @@ -143,4 +146,7 @@ int vkms_verify_crc_source(struct drm_crtc *crtc, const char *source_name,
>  			   size_t *values_cnt);
>  void vkms_crc_work_handle(struct work_struct *work);
>  
> +/* Writeback */
> +int enable_writeback_connector(struct vkms_device *vkmsdev);
> +
>  #endif /* _VKMS_DRV_H_ */
> diff --git a/drivers/gpu/drm/vkms/vkms_output.c b/drivers/gpu/drm/vkms/vkms_output.c
> index fb1941a6522c..3b093ae8f373 100644
> --- a/drivers/gpu/drm/vkms/vkms_output.c
> +++ b/drivers/gpu/drm/vkms/vkms_output.c
> @@ -84,6 +84,12 @@ int vkms_output_init(struct vkms_device *vkmsdev, int index)
>  		goto err_attach;
>  	}
>  
> +	if (enable_writeback) {
> +		ret = enable_writeback_connector(vkmsdev);
> +		if (ret)
> +			DRM_ERROR("Failed to init writeback connector\n");
> +	}
> +
>  	drm_mode_config_reset(dev);
>  
>  	return 0;
> diff --git a/drivers/gpu/drm/vkms/vkms_writeback.c b/drivers/gpu/drm/vkms/vkms_writeback.c
> new file mode 100644
> index 000000000000..56632eb393cb
> --- /dev/null
> +++ b/drivers/gpu/drm/vkms/vkms_writeback.c
> @@ -0,0 +1,166 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +
> +#include "vkms_drv.h"
> +#include "vkms_composer.h"
> +#include <drm/drm_writeback.h>
> +#include <drm/drm_probe_helper.h>
> +#include <drm/drm_atomic_helper.h>
> +#include <drm/drm_gem_framebuffer_helper.h>
> +
> +static const u32 vkms_wb_formats[] = {
> +	DRM_FORMAT_XRGB8888,
> +};
> +
> +static const struct drm_connector_funcs vkms_wb_connector_funcs = {
> +	.fill_modes = drm_helper_probe_single_connector_modes,
> +	.destroy = drm_connector_cleanup,
> +	.reset = drm_atomic_helper_connector_reset,
> +	.atomic_duplicate_state = drm_atomic_helper_connector_duplicate_state,
> +	.atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
> +};
> +
> +static int vkms_wb_encoder_atomic_check(struct drm_encoder *encoder,
> +					struct drm_crtc_state *crtc_state,
> +					struct drm_connector_state *conn_state)
> +{
> +	struct drm_framebuffer *fb;
> +	const struct drm_display_mode *mode = &crtc_state->mode;
> +
> +	if (!conn_state->writeback_job || !conn_state->writeback_job->fb)
> +		return 0;
> +
> +	fb = conn_state->writeback_job->fb;
> +	if (fb->width != mode->hdisplay || fb->height != mode->vdisplay) {
> +		DRM_DEBUG_KMS("Invalid framebuffer size %ux%u\n",
> +			      fb->width, fb->height);
> +		return -EINVAL;
> +	}
> +
> +	if (fb->format->format != DRM_FORMAT_XRGB8888) {
> +		struct drm_format_name_buf format_name;
> +
> +		DRM_DEBUG_KMS("Invalid pixel format %s\n",
> +			      drm_get_format_name(fb->format->format,
> +						  &format_name));
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
> +static const struct drm_encoder_helper_funcs vkms_wb_encoder_helper_funcs = {
> +	.atomic_check = vkms_wb_encoder_atomic_check,
> +};
> +
> +static int vkms_wb_connector_get_modes(struct drm_connector *connector)
> +{
> +	struct drm_device *dev = connector->dev;
> +
> +	return drm_add_modes_noedid(connector, dev->mode_config.max_width,
> +				    dev->mode_config.max_height);
> +}
> +
> +static int vkms_wb_prepare_job(struct drm_writeback_connector *wb_connector,
> +			       struct drm_writeback_job *job)
> +{
> +	struct vkms_gem_object *vkms_obj;
> +	struct drm_gem_object *gem_obj;
> +	int ret;
> +
> +	if (!job->fb)
> +		return 0;
> +
> +	gem_obj = drm_gem_fb_get_obj(job->fb, 0);
> +	ret = vkms_gem_vmap(gem_obj);
> +	if (ret) {
> +		DRM_ERROR("vmap failed: %d\n", ret);
> +		return ret;
> +	}
> +
> +	vkms_obj = drm_gem_to_vkms_gem(gem_obj);
> +	job->priv = vkms_obj->vaddr;
> +
> +	return 0;
> +}
> +
> +static void vkms_wb_cleanup_job(struct drm_writeback_connector *connector,
> +				struct drm_writeback_job *job)
> +{
> +	struct drm_gem_object *gem_obj;
> +
> +	if (!job->fb)
> +		return;
> +
> +	gem_obj = drm_gem_fb_get_obj(job->fb, 0);
> +	vkms_gem_vunmap(gem_obj);
> +}
> +
> +static void vkms_wb_atomic_commit(struct drm_connector *conn,
> +				  struct drm_connector_state *state)
> +{
> +	struct vkms_device *vkmsdev = drm_device_to_vkms_device(conn->dev);
> +	struct vkms_output *output = &vkmsdev->output;
> +	struct vkms_crtc_state *crtc_state = output->crc_state;
> +	struct drm_writeback_connector *wb_conn = &output->wb_connector;
> +	struct drm_connector_state *conn_state = wb_conn->base.state;
> +	void *priv_data = conn_state->writeback_job->priv;
> +	struct vkms_data *primary_data = NULL;
> +	struct vkms_data *cursor_data = NULL;
> +	struct drm_framebuffer *fb = NULL;
> +	struct vkms_gem_object *vkms_obj;
> +	struct drm_gem_object *gem_obj;
> +
> +	if (!conn_state)
> +		return;
> +
> +	if (!conn_state->writeback_job || !conn_state->writeback_job->fb) {
> +		DRM_DEBUG_DRIVER("Disable writeback\n");
> +		return;
> +	}
> +
> +	if (crtc_state->num_active_planes >= 1)
> +		primary_data = crtc_state->active_planes[0]->data;
> +
> +	if (crtc_state->num_active_planes == 2)
> +		cursor_data = crtc_state->active_planes[1]->data;
> +
> +	if (!primary_data)
> +		return;
> +
> +	fb = &primary_data->fb;
> +	gem_obj = drm_gem_fb_get_obj(fb, 0);
> +	vkms_obj = drm_gem_to_vkms_gem(gem_obj);
> +
> +	if (!vkms_obj->vaddr || !priv_data)
> +		return;
> +
> +	drm_writeback_queue_job(wb_conn, state);
> +
> +	memcpy(priv_data, vkms_obj->vaddr, vkms_obj->gem.size);
> +	if (cursor_data)
> +		compose_cursor(cursor_data, primary_data, priv_data);
> +
> +	drm_writeback_signal_completion(wb_conn, 0);
> +}
> +
> +static const struct drm_connector_helper_funcs vkms_wb_conn_helper_funcs = {
> +	.get_modes = vkms_wb_connector_get_modes,
> +	.prepare_writeback_job = vkms_wb_prepare_job,
> +	.cleanup_writeback_job = vkms_wb_cleanup_job,
> +	.atomic_commit = vkms_wb_atomic_commit,
> +};
> +
> +int enable_writeback_connector(struct vkms_device *vkmsdev)
> +{
> +	struct drm_writeback_connector *wb = &vkmsdev->output.wb_connector;
> +
> +	vkmsdev->output.wb_connector.encoder.possible_crtcs = 1;
> +	drm_connector_helper_add(&wb->base, &vkms_wb_conn_helper_funcs);
> +
> +	return drm_writeback_connector_init(&vkmsdev->drm, wb,
> +					    &vkms_wb_connector_funcs,
> +					    &vkms_wb_encoder_helper_funcs,
> +					    vkms_wb_formats,
> +					    ARRAY_SIZE(vkms_wb_formats));
> +}
> +
> -- 
> 2.21.0

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch