Generic framework for tracking internal interfaces
==================================================
Summary
-------
interface_tracker is a generic framework which allows to track appearance
and disappearance of different interfaces provided by kernel/driver code inside
the kernel. Examples of such interfaces: clocks, phys, regulators, drm_panel...
Interface is specified by a pair of object pointer and interface type. Object
type depends on interface type, for example interface type drm_panel determines
that object is a device_node. Object pointer is used to distinguish different
interfaces of the same type and should identify object the interface is bound to.
For example it could be DT node, struct device,...
The framework provides two functions for interface providers which should be
called just after interface becomes available or just before interface
removal. Interface consumers can register callback which will be called
when requested interface changes its state, if during callback registration
the interface is already up, notification will be sent also.
The framework allows nesting calls, for example it is possible to signal one
interface in tracker callback of another interface. It is done by putting
every request into the queue. If the queue is empty before adding
the request, the queue will be processed after, if there is already another
request in the queue it means the queue is already processed by different
thread so no additional action is required. With this pattern only spinlock
is necessary to protect the queue. However in case of removal of either
callback or interface caller should be sure that his request has been
processed so framework waits until the queue becomes empty, it is done using
completion mechanism.
The framework functions should not be called in atomic context. Callbacks
should be aware that they can be called in any time between registration and
de-registration, so they should use synchronization mechanisms carefully.
Callbacks should also avoid to perform time consuming tasks, the framework
serializes them, so it could stall other callbacks.
Use cases
---------
The interface is very generic, there are many situations it can be useful:
1. Replacement for subsystem specific methods of publishing/unpublishing
interfaces. Currently many frameworks allows only querying for presence of given
interface. In such cases client can defer probing or implement interface
polling, which is usually subobtimal. Additionally subsystems often do not
provide methods to signal to the consumers that they are about to be destroyed.
2. Monitoring for different interfaces provided by the same object. An example
should explain it better. Lets assume in device tree drm crtc device node have
video link to another node, so it knows only that there is something connected
to its RGB output. It can be a RGB panel (drm_panel framework), it can be an
image enhancer (SoC specific framework) or it can be some signal converter
(drm_encoder, drm_bridge, drm_encoder_slave...). Driver have only phandle to
another node. Currently it is difficult to handle such situations in a generic
way. interface_tracker should make it simple: crtc should monitor all supported
interface types that appears at the device_node pointed by the phandle.
Potential use cases
-------------------
Points mentioned above were the reasons for writing this framework. During
development I have realized that this framework can be also useful for other
tasks.
3. Replacement for deferred probing - if for some reason driver do not wants to
defer but it requires given resources it can use interface_tracker. It should be
possible to create an helper which will wait for appearance of all interfaces
from a given list, and 'continue' probe only when all resources becomes
available.
4. Replacement or helper for subsystem specific solutions:
- V4L2 subdev async registration,
- component framework.
Both frameworks solves a problem of tracking sub-components (un-)registration
by master device, it should be possible to do the same with interface_tracker
framework. Some additional helpers can be convienent to make the implementation
easier.
5. Cure the situation with sysfs 'unbind' property. Currently many drivers are
providers of different resources/interfaces: regulators, clocks, phys,
V4L2 subdevs, ... They are usually protected from module unloading by getting
module reference, but there is no protection from driver unbinding using sysfs
method: echo 'device' >/sys/bus/.../drivers/.../unbind. After unbind consumer
stays with the pointer to non-existing object, next time it tries to use it
system usually crashes. interface_tracker do not add any protection, but it adds
a way to signal to the consumer that given resource will disappear. It allows
to handle such situations more gently.
Potential issues/extensions
---------------------------
1. Scalability - the framework serializes all tasks and callbacks. In case there
are no many users it should not be a problem. If the number of users grows there
are different options to consider:
- run callbacks in parallel, I guess async_schedule_domain can be helpfull,
- partition trackers, for example per interface types - different interface
types will use different internal queues/lists.
2. Complication of code - asynchronous programming usually seems to be more
complicated. Adding some helpers could make it less painfull.
3. Object comparison - currently object pointers are compared by value, it could
be desirable to allow also other ways of comparison, for example string
comparison. It is not a problem to extend the framework.
TODO
----
1. Testing - the patchset have not been tested yet with multiple users.
2. Add tracker support in other frameworks - currently there is only drm_panel.
I plan also to add something more complicated, for example use it in
exynos_drm to track components. If there is positive feedback I can try
to add also other frameworks.
3. devm_* registration.
4. Helpers - as the situation 'wait for number interfaces before continue'
seems to be quite common, some helper to easy handling it could be useful.
Final remarks
-------------
Primarily I have planned notifications for DRM panels. Next I have realized
something similar would be necessary for drm_bridge. Discussions with other
developers showed to me that it could be useful in many other areas. I am not
sure if other developers agree with adding it to things like regulators, clocks,
phys, but I will be glad if it can be used at least with drm_panel.
Regards
Andrzej
Andrzej Hajda (4):
drivers/base: add interface tracker framework
drm/panel: add interface tracker support
drm/exynos/dpi: add interface tracker support
drm/panel/ld9040: do not power off panel on removal
drivers/base/Makefile | 2 +-
drivers/base/interface_tracker.c | 307 ++++++++++++++++++++++++++++++++
drivers/gpu/drm/drm_panel.c | 5 +
drivers/gpu/drm/exynos/exynos_drm_dpi.c | 58 ++++--
drivers/gpu/drm/panel/panel-ld9040.c | 1 -
include/linux/interface_tracker.h | 29 +++
6 files changed, 389 insertions(+), 13 deletions(-)
create mode 100644 drivers/base/interface_tracker.c
create mode 100644 include/linux/interface_tracker.h
--
1.8.3.2
interface_tracker is a generic framework which allows to track appearance
and disappearance of different interfaces provided by kernel/driver code inside
the kernel. Examples of such interfaces: clocks, phys, regulators, drm_panel...
Interface is specified by a pair of object pointer and interface type. Object
type depends on interface type, for example interface type drm_panel determines
that object is a device_node. Object pointer is used to distinguish different
interfaces of the same type and should identify object the interface is bound to.
Signed-off-by: Andrzej Hajda <[email protected]>
---
drivers/base/Makefile | 2 +-
drivers/base/interface_tracker.c | 307 ++++++++++++++++++++++++++++++++++++++
include/linux/interface_tracker.h | 27 ++++
3 files changed, 335 insertions(+), 1 deletion(-)
create mode 100644 drivers/base/interface_tracker.c
create mode 100644 include/linux/interface_tracker.h
diff --git a/drivers/base/Makefile b/drivers/base/Makefile
index 04b314e..5a45c41 100644
--- a/drivers/base/Makefile
+++ b/drivers/base/Makefile
@@ -4,7 +4,7 @@ obj-y := component.o core.o bus.o dd.o syscore.o \
driver.o class.o platform.o \
cpu.o firmware.o init.o map.o devres.o \
attribute_container.o transport_class.o \
- topology.o container.o
+ topology.o container.o interface_tracker.o
obj-$(CONFIG_DEVTMPFS) += devtmpfs.o
obj-$(CONFIG_DMA_CMA) += dma-contiguous.o
obj-y += power/
diff --git a/drivers/base/interface_tracker.c b/drivers/base/interface_tracker.c
new file mode 100644
index 0000000..3d36cba
--- /dev/null
+++ b/drivers/base/interface_tracker.c
@@ -0,0 +1,307 @@
+/*
+ * Generic framework for tracking kernel interfaces
+ *
+ * Copyright (c) 2014 Samsung Electronics Co., Ltd
+ * Andrzej Hajda <[email protected]>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * interface_tracker is a generic framework which allows to track appearance
+ * and disappearance of different interfaces provided by kernel/driver code
+ * inside the kernel. Examples of such interfaces: clocks, phys, regulators,
+ * drm_panel...
+ * Interface is specified by a pair of object pointer and interface type. Object
+ * type depends on interface type, for example interface type drm_panel
+ * determines that object is a device_node. Object pointer is used
+ * to distinguish different interfaces of the same type and should identify
+ * object the interface is bound to. For example it could be DT node,
+ * struct device...
+ *
+ * The framework provides two functions for interface providers which should be
+ * called just after interface becomes available or just before interface
+ * removal. Interface consumers can register callback which will be called when
+ * the requested interface changes its state, if during callback registration
+ * the interface is already up, notification will be sent also.
+ *
+ * The framework allows nesting calls, for example it is possible to signal one
+ * interface in tracker callback of another interface. It is done by putting
+ * every request into the queue. If the queue is empty before adding
+ * the request, the queue will be processed after, if there is already another
+ * request in the queue it means the queue is already processed by different
+ * thread so no additional action is required. With this pattern only spinlock
+ * is necessary to protect the queue. However in case of removal of either
+ * callback or interface caller should be sure that his request has been
+ * processed so framework waits until the queue becomes empty, it is done using
+ * completion mechanism.
+ * The framework functions should not be called in atomic context. Callbacks
+ * should be aware that they can be called in any time between registration and
+ * unregistration, so they should use synchronization mechanisms carefully.
+ * Callbacks should also avoid to perform time consuming tasks, the framework
+ * serializes them, so it could stall other callbacks.
+ */
+
+#include <linux/completion.h>
+#include <linux/interface_tracker.h>
+#include <linux/list.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+
+enum interface_tracker_task_id {
+ interface_tracker_task_register,
+ interface_tracker_task_unregister,
+ interface_tracker_task_ifup,
+ interface_tracker_task_ifdown,
+};
+
+struct interface_tracker_task {
+ struct list_head list;
+ enum interface_tracker_task_id task_id;
+
+ const void *object;
+ unsigned long type;
+ union {
+ struct interface_tracker_block *itb;
+ void *data;
+ };
+};
+
+struct interface_tracker_node {
+ struct list_head list;
+ struct list_head itb_head;
+ const void *object;
+ unsigned long type;
+ void *data;
+ bool ifup;
+};
+
+static LIST_HEAD(interface_tracker_queue);
+static DEFINE_SPINLOCK(interface_tracker_queue_lock);
+static DECLARE_COMPLETION(interface_tracker_queue_completion);
+
+static LIST_HEAD(interface_tracker_nodes);
+
+static struct interface_tracker_node *
+interface_tracker_get_node(const void *object, unsigned long type, bool create)
+{
+ struct interface_tracker_node *node;
+
+ list_for_each_entry(node, &interface_tracker_nodes, list) {
+ if (node->type == type && node->object == object)
+ return node;
+ }
+
+ if (!create)
+ return NULL;
+
+ node = kmalloc(sizeof(*node), GFP_KERNEL);
+ node->object = object;
+ node->type = type;
+ node->ifup = false;
+ INIT_LIST_HEAD(&node->itb_head);
+ list_add(&node->list, &interface_tracker_nodes);
+
+ return node;
+}
+
+static void interface_tracker_process_task(struct interface_tracker_task *task)
+{
+ struct interface_tracker_block *itb;
+ struct interface_tracker_node *node;
+
+ switch (task->task_id) {
+ case interface_tracker_task_register:
+ node = interface_tracker_get_node(task->object, task->type,
+ true);
+ list_add_tail(&task->itb->list, &node->itb_head);
+
+ if (node->ifup)
+ task->itb->callback(task->itb, task->object, task->type,
+ true, node->data);
+ return;
+ case interface_tracker_task_unregister:
+ node = interface_tracker_get_node(task->object, task->type,
+ false);
+ if (WARN_ON(!node))
+ return;
+
+ list_for_each_entry(itb, &node->itb_head, list) {
+ if (itb != task->itb)
+ continue;
+ list_del(&itb->list);
+ if (list_empty(&node->itb_head)) {
+ list_del(&node->list);
+ kfree(node);
+ }
+ return;
+ }
+
+ WARN_ON(true);
+
+ return;
+ case interface_tracker_task_ifup:
+ node = interface_tracker_get_node(task->object, task->type,
+ true);
+
+ if (WARN_ON(node->ifup))
+ return;
+
+ node->ifup = true;
+ node->data = task->data;
+ list_for_each_entry(itb, &node->itb_head, list)
+ itb->callback(itb, task->object, task->type, true,
+ node->data);
+ return;
+ case interface_tracker_task_ifdown:
+ node = interface_tracker_get_node(task->object, task->type,
+ false);
+
+ if (WARN_ON(!node))
+ return;
+
+ WARN_ON(!node->ifup);
+
+ if (list_empty(&node->itb_head)) {
+ list_del(&node->list);
+ kfree(node);
+ return;
+ }
+
+ node->ifup = false;
+ node->data = task->data;
+
+ list_for_each_entry(itb, &node->itb_head, list)
+ itb->callback(itb, task->object, task->type, false,
+ node->data);
+ }
+}
+
+static int interface_tracker_process_queue(void)
+{
+ struct interface_tracker_task *task, *ptask = NULL;
+ unsigned long flags;
+ bool empty;
+
+ /* Queue non-emptiness is used as a sentinel to prevent processing
+ * by multiple threads, so we cannot delete entry from the queue
+ * until it is processed.
+ */
+ while (true) {
+ spin_lock_irqsave(&interface_tracker_queue_lock, flags);
+
+ if (ptask)
+ list_del(&ptask->list);
+ task = list_first_entry(&interface_tracker_queue,
+ struct interface_tracker_task, list);
+
+ empty = list_empty(&interface_tracker_queue);
+ if (empty)
+ complete_all(&interface_tracker_queue_completion);
+
+ spin_unlock_irqrestore(&interface_tracker_queue_lock, flags);
+
+ if (ptask)
+ kfree(ptask);
+
+ if (empty)
+ break;
+
+ interface_tracker_process_task(task);
+ ptask = task;
+ }
+
+ return 0;
+}
+
+static int interface_tracker_add_task(struct interface_tracker_task *task,
+ bool sync)
+{
+ unsigned long flags;
+ int ret = 0;
+ bool empty;
+
+ spin_lock_irqsave(&interface_tracker_queue_lock, flags);
+
+ empty = list_empty(&interface_tracker_queue);
+ if (empty)
+ reinit_completion(&interface_tracker_queue_completion);
+
+ list_add(&task->list, &interface_tracker_queue);
+
+ spin_unlock_irqrestore(&interface_tracker_queue_lock, flags);
+
+ if (empty) {
+ ret = interface_tracker_process_queue();
+ }else if (sync) {
+ wait_for_completion(&interface_tracker_queue_completion);
+ }
+
+ return ret;
+}
+
+int interface_tracker_register(const void *object, unsigned long type,
+ struct interface_tracker_block *itb)
+{
+ struct interface_tracker_task *task;
+
+ task = kmalloc(sizeof(*task), GFP_KERNEL);
+ if (!task)
+ return -ENOMEM;
+
+ task->task_id = interface_tracker_task_register;
+ task->object = object;
+ task->type = type;
+ task->itb = itb;
+
+ return interface_tracker_add_task(task, false);
+}
+
+int interface_tracker_unregister(const void *object, unsigned long type,
+ struct interface_tracker_block *itb)
+{
+ struct interface_tracker_task *task;
+
+ task = kmalloc(sizeof(*task), GFP_KERNEL);
+ if (!task)
+ return -ENOMEM;
+
+ task->task_id = interface_tracker_task_unregister;
+ task->object = object;
+ task->type = type;
+ task->itb = itb;
+
+ return interface_tracker_add_task(task, true);
+}
+
+int interface_tracker_ifup(const void *object, unsigned long type, void *data)
+{
+ struct interface_tracker_task *task;
+
+ task = kmalloc(sizeof(*task), GFP_KERNEL);
+ if (!task)
+ return -ENOMEM;
+
+ task->task_id = interface_tracker_task_ifup;
+ task->object = object;
+ task->type = type;
+ task->data = data;
+
+ return interface_tracker_add_task(task, false);
+}
+
+int interface_tracker_ifdown(const void *object, unsigned long type, void *data)
+{
+ struct interface_tracker_task *task;
+
+ task = kmalloc(sizeof(*task), GFP_KERNEL);
+ if (!task)
+ return -ENOMEM;
+
+ task->task_id = interface_tracker_task_ifdown;
+ task->object = object;
+ task->type = type;
+ task->data = data;
+
+ return interface_tracker_add_task(task, true);
+}
diff --git a/include/linux/interface_tracker.h b/include/linux/interface_tracker.h
new file mode 100644
index 0000000..e1eff00
--- /dev/null
+++ b/include/linux/interface_tracker.h
@@ -0,0 +1,27 @@
+#ifndef INTERFACE_TRACKER_H
+#define INTERFACE_TRACKER_H
+
+#include <linux/types.h>
+
+struct list_head;
+struct interface_tracker_block;
+
+typedef void (*interface_tracker_fn_t)(struct interface_tracker_block *itb,
+ const void *object, unsigned long type,
+ bool on, void *data);
+
+struct interface_tracker_block {
+ interface_tracker_fn_t callback;
+ struct list_head list;
+};
+
+extern int interface_tracker_register(const void *object, unsigned long type,
+ struct interface_tracker_block *itb);
+extern int interface_tracker_unregister(const void *object, unsigned long type,
+ struct interface_tracker_block *itb);
+extern int interface_tracker_ifup(const void *object, unsigned long type,
+ void *data);
+extern int interface_tracker_ifdown(const void *object, unsigned long type,
+ void *data);
+
+#endif /* INTERFACE_TRACKER_H */
--
1.8.3.2
exynos_dpi uses connector polling for tracking panel presence,
this solution introduces unnecessary 10s delay before panel activation.
Moreover it is unsafe, module unloading or driver unbinding can
cause system crash. interface_tracker support solves both problems.
Signed-off-by: Andrzej Hajda <[email protected]>
---
drivers/gpu/drm/exynos/exynos_drm_dpi.c | 58 ++++++++++++++++++++++++++-------
1 file changed, 47 insertions(+), 11 deletions(-)
diff --git a/drivers/gpu/drm/exynos/exynos_drm_dpi.c b/drivers/gpu/drm/exynos/exynos_drm_dpi.c
index 2b09c7c..4c6682f 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_dpi.c
+++ b/drivers/gpu/drm/exynos/exynos_drm_dpi.c
@@ -14,6 +14,7 @@
#include <drm/drm_crtc_helper.h>
#include <drm/drm_panel.h>
+#include <linux/interface_tracker.h>
#include <linux/regulator/consumer.h>
#include <video/of_videomode.h>
@@ -21,6 +22,8 @@
#include "exynos_drm_drv.h"
+static void exynos_dpi_dpms(struct exynos_drm_display *display, int mode);
+
struct exynos_dpi {
struct device *dev;
struct device_node *panel_node;
@@ -28,6 +31,7 @@ struct exynos_dpi {
struct drm_panel *panel;
struct drm_connector connector;
struct drm_encoder *encoder;
+ struct interface_tracker_block itb;
struct videomode *vm;
int dpms_mode;
@@ -41,15 +45,9 @@ exynos_dpi_detect(struct drm_connector *connector, bool force)
struct exynos_dpi *ctx = connector_to_dpi(connector);
/* panels supported only by boot-loader are always connected */
- if (!ctx->panel_node)
+ if (ctx->vm)
return connector_status_connected;
- if (!ctx->panel) {
- ctx->panel = of_drm_find_panel(ctx->panel_node);
- if (ctx->panel)
- drm_panel_attach(ctx->panel, &ctx->connector);
- }
-
if (ctx->panel)
return connector_status_connected;
@@ -114,6 +112,28 @@ static struct drm_connector_helper_funcs exynos_dpi_connector_helper_funcs = {
.best_encoder = exynos_dpi_best_encoder,
};
+void exynos_dpi_notifier(struct interface_tracker_block *itb,
+ const void *object, unsigned long type, bool on,
+ void *data)
+{
+ struct exynos_dpi *ctx = container_of(itb, struct exynos_dpi, itb);
+
+ mutex_lock(&ctx->connector.dev->mode_config.mutex);
+ if (on) {
+ ctx->panel = data;
+ drm_panel_attach(ctx->panel, &ctx->connector);
+ } else {
+ struct exynos_drm_display *display;
+
+ display = platform_get_drvdata(to_platform_device(ctx->dev));
+ exynos_dpi_dpms(display, DRM_MODE_DPMS_OFF);
+ drm_panel_detach(ctx->panel);
+ ctx->panel = NULL;
+ }
+ mutex_unlock(&ctx->connector.dev->mode_config.mutex);
+ drm_helper_hpd_irq_event(ctx->connector.dev);
+}
+
static int exynos_dpi_create_connector(struct exynos_drm_display *display,
struct drm_encoder *encoder)
{
@@ -123,10 +143,7 @@ static int exynos_dpi_create_connector(struct exynos_drm_display *display,
ctx->encoder = encoder;
- if (ctx->panel_node)
- connector->polled = DRM_CONNECTOR_POLL_CONNECT;
- else
- connector->polled = DRM_CONNECTOR_POLL_HPD;
+ connector->polled = DRM_CONNECTOR_POLL_HPD;
ret = drm_connector_init(encoder->dev, connector,
&exynos_dpi_connector_funcs,
@@ -140,9 +157,27 @@ static int exynos_dpi_create_connector(struct exynos_drm_display *display,
drm_sysfs_connector_add(connector);
drm_mode_connector_attach_encoder(connector, encoder);
+ if (ctx->panel_node) {
+ ctx->itb.callback = exynos_dpi_notifier;
+ interface_tracker_register(ctx->panel_node,
+ INTERFACE_TRACKER_TYPE_DRM_PANEL,
+ &ctx->itb);
+ }
+
return 0;
}
+static void exynos_dpi_display_remove(struct exynos_drm_display *display)
+{
+ struct exynos_dpi *ctx = display->ctx;
+
+ if (ctx->panel_node) {
+ interface_tracker_unregister(ctx->panel_node,
+ INTERFACE_TRACKER_TYPE_DRM_PANEL,
+ &ctx->itb);
+ }
+}
+
static void exynos_dpi_poweron(struct exynos_dpi *ctx)
{
if (ctx->panel)
@@ -178,6 +213,7 @@ static void exynos_dpi_dpms(struct exynos_drm_display *display, int mode)
static struct exynos_drm_display_ops exynos_dpi_display_ops = {
.create_connector = exynos_dpi_create_connector,
+ .remove = exynos_dpi_display_remove,
.dpms = exynos_dpi_dpms
};
--
1.8.3.2
Panel is powered off already by connector during drm_panel_remove call.
Signed-off-by: Andrzej Hajda <[email protected]>
---
drivers/gpu/drm/panel/panel-ld9040.c | 1 -
1 file changed, 1 deletion(-)
diff --git a/drivers/gpu/drm/panel/panel-ld9040.c b/drivers/gpu/drm/panel/panel-ld9040.c
index 1f1f837..1def4b0 100644
--- a/drivers/gpu/drm/panel/panel-ld9040.c
+++ b/drivers/gpu/drm/panel/panel-ld9040.c
@@ -348,7 +348,6 @@ static int ld9040_remove(struct spi_device *spi)
{
struct ld9040 *ctx = spi_get_drvdata(spi);
- ld9040_power_off(ctx);
drm_panel_remove(&ctx->panel);
return 0;
--
1.8.3.2
drm_panel framework allows only query for presence of given panel.
It also does not protect panel module from unloading and does not
provide solution for driver unbinding. interface_tracker
should solve both issues.
Signed-off-by: Andrzej Hajda <[email protected]>
---
---
drivers/gpu/drm/drm_panel.c | 5 +++++
include/linux/interface_tracker.h | 2 ++
2 files changed, 7 insertions(+)
diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
index 2ef988e..72a3c5c 100644
--- a/drivers/gpu/drm/drm_panel.c
+++ b/drivers/gpu/drm/drm_panel.c
@@ -22,6 +22,7 @@
*/
#include <linux/err.h>
+#include <linux/interface_tracker.h>
#include <linux/module.h>
#include <drm/drm_crtc.h>
@@ -41,6 +42,8 @@ int drm_panel_add(struct drm_panel *panel)
mutex_lock(&panel_lock);
list_add_tail(&panel->list, &panel_list);
mutex_unlock(&panel_lock);
+ interface_tracker_ifup(panel->dev->of_node,
+ INTERFACE_TRACKER_TYPE_DRM_PANEL, panel);
return 0;
}
@@ -48,6 +51,8 @@ EXPORT_SYMBOL(drm_panel_add);
void drm_panel_remove(struct drm_panel *panel)
{
+ interface_tracker_ifdown(panel->dev->of_node,
+ INTERFACE_TRACKER_TYPE_DRM_PANEL, panel);
mutex_lock(&panel_lock);
list_del_init(&panel->list);
mutex_unlock(&panel_lock);
diff --git a/include/linux/interface_tracker.h b/include/linux/interface_tracker.h
index e1eff00..0a08cba 100644
--- a/include/linux/interface_tracker.h
+++ b/include/linux/interface_tracker.h
@@ -6,6 +6,8 @@
struct list_head;
struct interface_tracker_block;
+#define INTERFACE_TRACKER_TYPE_DRM_PANEL 1
+
typedef void (*interface_tracker_fn_t)(struct interface_tracker_block *itb,
const void *object, unsigned long type,
bool on, void *data);
--
1.8.3.2
On Wed, Apr 30, 2014 at 04:02:50PM +0200, Andrzej Hajda wrote:
> Generic framework for tracking internal interfaces
> ==================================================
>
> Summary
> -------
>
> interface_tracker is a generic framework which allows to track appearance
> and disappearance of different interfaces provided by kernel/driver code inside
> the kernel. Examples of such interfaces: clocks, phys, regulators, drm_panel...
> Interface is specified by a pair of object pointer and interface type. Object
> type depends on interface type, for example interface type drm_panel determines
> that object is a device_node. Object pointer is used to distinguish different
> interfaces of the same type and should identify object the interface is bound to.
> For example it could be DT node, struct device,...
>
> The framework provides two functions for interface providers which should be
> called just after interface becomes available or just before interface
> removal. Interface consumers can register callback which will be called
> when requested interface changes its state, if during callback registration
> the interface is already up, notification will be sent also.
>
> The framework allows nesting calls, for example it is possible to signal one
> interface in tracker callback of another interface. It is done by putting
> every request into the queue. If the queue is empty before adding
> the request, the queue will be processed after, if there is already another
> request in the queue it means the queue is already processed by different
> thread so no additional action is required. With this pattern only spinlock
> is necessary to protect the queue. However in case of removal of either
> callback or interface caller should be sure that his request has been
> processed so framework waits until the queue becomes empty, it is done using
> completion mechanism.
>
> The framework functions should not be called in atomic context. Callbacks
> should be aware that they can be called in any time between registration and
> de-registration, so they should use synchronization mechanisms carefully.
> Callbacks should also avoid to perform time consuming tasks, the framework
> serializes them, so it could stall other callbacks.
>
> Use cases
> ---------
>
> The interface is very generic, there are many situations it can be useful:
>
> 1. Replacement for subsystem specific methods of publishing/unpublishing
> interfaces. Currently many frameworks allows only querying for presence of given
> interface. In such cases client can defer probing or implement interface
> polling, which is usually subobtimal. Additionally subsystems often do not
> provide methods to signal to the consumers that they are about to be destroyed.
>
> 2. Monitoring for different interfaces provided by the same object. An example
> should explain it better. Lets assume in device tree drm crtc device node have
> video link to another node, so it knows only that there is something connected
> to its RGB output. It can be a RGB panel (drm_panel framework), it can be an
> image enhancer (SoC specific framework) or it can be some signal converter
> (drm_encoder, drm_bridge, drm_encoder_slave...). Driver have only phandle to
> another node. Currently it is difficult to handle such situations in a generic
> way. interface_tracker should make it simple: crtc should monitor all supported
> interface types that appears at the device_node pointed by the phandle.
>
> Potential use cases
> -------------------
>
> Points mentioned above were the reasons for writing this framework. During
> development I have realized that this framework can be also useful for other
> tasks.
>
> 3. Replacement for deferred probing - if for some reason driver do not wants to
> defer but it requires given resources it can use interface_tracker. It should be
> possible to create an helper which will wait for appearance of all interfaces
> from a given list, and 'continue' probe only when all resources becomes
> available.
>
> 4. Replacement or helper for subsystem specific solutions:
> - V4L2 subdev async registration,
> - component framework.
> Both frameworks solves a problem of tracking sub-components (un-)registration
> by master device, it should be possible to do the same with interface_tracker
> framework. Some additional helpers can be convienent to make the implementation
> easier.
>
> 5. Cure the situation with sysfs 'unbind' property. Currently many drivers are
> providers of different resources/interfaces: regulators, clocks, phys,
> V4L2 subdevs, ... They are usually protected from module unloading by getting
> module reference, but there is no protection from driver unbinding using sysfs
> method: echo 'device' >/sys/bus/.../drivers/.../unbind. After unbind consumer
> stays with the pointer to non-existing object, next time it tries to use it
> system usually crashes. interface_tracker do not add any protection, but it adds
> a way to signal to the consumer that given resource will disappear. It allows
> to handle such situations more gently.
>
> Potential issues/extensions
> ---------------------------
>
> 1. Scalability - the framework serializes all tasks and callbacks. In case there
> are no many users it should not be a problem. If the number of users grows there
> are different options to consider:
> - run callbacks in parallel, I guess async_schedule_domain can be helpfull,
> - partition trackers, for example per interface types - different interface
> types will use different internal queues/lists.
>
> 2. Complication of code - asynchronous programming usually seems to be more
> complicated. Adding some helpers could make it less painfull.
>
> 3. Object comparison - currently object pointers are compared by value, it could
> be desirable to allow also other ways of comparison, for example string
> comparison. It is not a problem to extend the framework.
>
> TODO
> ----
>
> 1. Testing - the patchset have not been tested yet with multiple users.
That's not good :)
What's wrong with the existing container code in the driver core, or the
component code? Shouldn't either of those work properly for you? Or
the managed token interface being proposed, how does that tie in here?
> 2. Add tracker support in other frameworks - currently there is only drm_panel.
> I plan also to add something more complicated, for example use it in
> exynos_drm to track components. If there is positive feedback I can try
> to add also other frameworks.
> 3. devm_* registration.
> 4. Helpers - as the situation 'wait for number interfaces before continue'
> seems to be quite common, some helper to easy handling it could be useful.
>
> Final remarks
> -------------
>
> Primarily I have planned notifications for DRM panels. Next I have realized
> something similar would be necessary for drm_bridge. Discussions with other
> developers showed to me that it could be useful in many other areas. I am not
> sure if other developers agree with adding it to things like regulators, clocks,
> phys, but I will be glad if it can be used at least with drm_panel.
Shouldn't the component code handle your DRM panels today?
thanks,
greg k-h
Hi Greg,
Thanks for comments. I CC Laurent, I hope it could be interesting for
him also.
Greg Kroah-Hartman wrote, On 30.04.2014 17:49:
> On Wed, Apr 30, 2014 at 04:02:50PM +0200, Andrzej Hajda wrote:
>> Generic framework for tracking internal interfaces
>> ==================================================
>>
>> Summary
>> -------
>>
>> interface_tracker is a generic framework which allows to track appearance
>> and disappearance of different interfaces provided by kernel/driver code inside
>> the kernel. Examples of such interfaces: clocks, phys, regulators, drm_panel...
>> Interface is specified by a pair of object pointer and interface type. Object
>> type depends on interface type, for example interface type drm_panel determines
>> that object is a device_node. Object pointer is used to distinguish different
>> interfaces of the same type and should identify object the interface is bound to.
>> For example it could be DT node, struct device,...
>>
>> The framework provides two functions for interface providers which should be
>> called just after interface becomes available or just before interface
>> removal. Interface consumers can register callback which will be called
>> when requested interface changes its state, if during callback registration
>> the interface is already up, notification will be sent also.
>>
>> The framework allows nesting calls, for example it is possible to signal one
>> interface in tracker callback of another interface. It is done by putting
>> every request into the queue. If the queue is empty before adding
>> the request, the queue will be processed after, if there is already another
>> request in the queue it means the queue is already processed by different
>> thread so no additional action is required. With this pattern only spinlock
>> is necessary to protect the queue. However in case of removal of either
>> callback or interface caller should be sure that his request has been
>> processed so framework waits until the queue becomes empty, it is done using
>> completion mechanism.
>>
>> The framework functions should not be called in atomic context. Callbacks
>> should be aware that they can be called in any time between registration and
>> de-registration, so they should use synchronization mechanisms carefully.
>> Callbacks should also avoid to perform time consuming tasks, the framework
>> serializes them, so it could stall other callbacks.
>>
>> Use cases
>> ---------
>>
>> The interface is very generic, there are many situations it can be useful:
>>
>> 1. Replacement for subsystem specific methods of publishing/unpublishing
>> interfaces. Currently many frameworks allows only querying for presence of given
>> interface. In such cases client can defer probing or implement interface
>> polling, which is usually subobtimal. Additionally subsystems often do not
>> provide methods to signal to the consumers that they are about to be destroyed.
>>
>> 2. Monitoring for different interfaces provided by the same object. An example
>> should explain it better. Lets assume in device tree drm crtc device node have
>> video link to another node, so it knows only that there is something connected
>> to its RGB output. It can be a RGB panel (drm_panel framework), it can be an
>> image enhancer (SoC specific framework) or it can be some signal converter
>> (drm_encoder, drm_bridge, drm_encoder_slave...). Driver have only phandle to
>> another node. Currently it is difficult to handle such situations in a generic
>> way. interface_tracker should make it simple: crtc should monitor all supported
>> interface types that appears at the device_node pointed by the phandle.
>>
>> Potential use cases
>> -------------------
>>
>> Points mentioned above were the reasons for writing this framework. During
>> development I have realized that this framework can be also useful for other
>> tasks.
>>
>> 3. Replacement for deferred probing - if for some reason driver do not wants to
>> defer but it requires given resources it can use interface_tracker. It should be
>> possible to create an helper which will wait for appearance of all interfaces
>> from a given list, and 'continue' probe only when all resources becomes
>> available.
>>
>> 4. Replacement or helper for subsystem specific solutions:
>> - V4L2 subdev async registration,
>> - component framework.
>> Both frameworks solves a problem of tracking sub-components (un-)registration
>> by master device, it should be possible to do the same with interface_tracker
>> framework. Some additional helpers can be convienent to make the implementation
>> easier.
>>
>> 5. Cure the situation with sysfs 'unbind' property. Currently many drivers are
>> providers of different resources/interfaces: regulators, clocks, phys,
>> V4L2 subdevs, ... They are usually protected from module unloading by getting
>> module reference, but there is no protection from driver unbinding using sysfs
>> method: echo 'device' >/sys/bus/.../drivers/.../unbind. After unbind consumer
>> stays with the pointer to non-existing object, next time it tries to use it
>> system usually crashes. interface_tracker do not add any protection, but it adds
>> a way to signal to the consumer that given resource will disappear. It allows
>> to handle such situations more gently.
>>
>> Potential issues/extensions
>> ---------------------------
>>
>> 1. Scalability - the framework serializes all tasks and callbacks. In case there
>> are no many users it should not be a problem. If the number of users grows there
>> are different options to consider:
>> - run callbacks in parallel, I guess async_schedule_domain can be helpfull,
>> - partition trackers, for example per interface types - different interface
>> types will use different internal queues/lists.
>>
>> 2. Complication of code - asynchronous programming usually seems to be more
>> complicated. Adding some helpers could make it less painfull.
>>
>> 3. Object comparison - currently object pointers are compared by value, it could
>> be desirable to allow also other ways of comparison, for example string
>> comparison. It is not a problem to extend the framework.
>>
>> TODO
>> ----
>>
>> 1. Testing - the patchset have not been tested yet with multiple users.
>
> That's not good :)
I would treat this series as a real RFC, with code which can be easily
tested by volunteers but as for RFC I am asking for comments if the idea
is OK and the patchset have chances to be accepted.
Anyway, I have performed some basic tests and it works :)
>
> What's wrong with the existing container code in the driver core, or the
> component code? Shouldn't either of those work properly for you? Or
> the managed token interface being proposed, how does that tie in here?
Container code seems to solve very specific problem, not really relevant
to this patchset. The component code would solve a very specific part of
problems this framework solves as described in use cases above. On the
other side problems which components solves are
solvable with this framework.
Managed token interface is about sharing 'named' resources it is not
connected with interface tracking.
>
>> 2. Add tracker support in other frameworks - currently there is only drm_panel.
>> I plan also to add something more complicated, for example use it in
>> exynos_drm to track components. If there is positive feedback I can try
>> to add also other frameworks.
>> 3. devm_* registration.
>> 4. Helpers - as the situation 'wait for number interfaces before continue'
>> seems to be quite common, some helper to easy handling it could be useful.
>>
>> Final remarks
>> -------------
>>
>> Primarily I have planned notifications for DRM panels. Next I have realized
>> something similar would be necessary for drm_bridge. Discussions with other
>> developers showed to me that it could be useful in many other areas. I am not
>> sure if other developers agree with adding it to things like regulators, clocks,
>> phys, but I will be glad if it can be used at least with drm_panel.
>
> Shouldn't the component code handle your DRM panels today?
I should correct my last sentence to this:
I will be glad if it can be used at least with video interfaces, ie.
drm_panel, video encoders/bridges, image enhancers.
The main problem with component framework is that componentization
significantly changes every driver and changes it in a way which is not
compatible with traditional drivers, so devices which are intended to
work with different DRM masters are hard to componentize if some of DRMs
are componentized and some not.
If you look at interface_tracker framework it achieves the same goal
as componentization without even touching panel drivers, look at 2nd
patch of the patchset - it adds interface_tracker support for all panels
with 7 lines of code in drm_panel framework and of course the
change is backward compatible.
Adding interface_tracker support to the 'master' requires more work:
1. registration of the callback.
2. unregistration of the callback.
3. the callback code.
But it is still much less than in case of components.
And interface_tracker framework allows much more, as I described in "Use
cases" and "Potential use cases" sections.
Regards
Andrzej
>
> thanks,
>
> greg k-h
>
On Wed, Apr 30, 2014 at 11:42:09PM +0200, Andrzej Hajda wrote:
> The main problem with component framework is that componentization
> significantly changes every driver and changes it in a way which is not
> compatible with traditional drivers, so devices which are intended to
> work with different DRM masters are hard to componentize if some of DRMs
> are componentized and some not.
Many of the problems which the component helpers are designed to solve
are those where you need the drm_device structure (or snd_card, or whatever
subsystem specific card/device representation structure) pre-created in
order to initialise the components.
In the case of DRM, you can't initialise encoders or connectors without
their drm_device structure pre-existing - because these components are
attached to the drm_device.
Your solution to that is to delay those calls, but the DRM subsystem is
not designed to cope like that - it's designed such that when the
connector or encoder initialisation functions are called, it is assumed
that the driver is initialising its state. (I've raised this point before
but you've just fobbed it off in the past.)
Another issue here is that the order of initialisation matters greatly.
Take CRTCs for example. In DRM, the order of attachment of CRTCs defines
their identity, changing the order changes their identity, and changes
how they are bound to their respective connectors.
--
FTTC broadband for 0.8mile line: now at 9.7Mbps down 460kbps up... slowly
improving, and getting towards what was expected from it.