On 11/02/2018 01:31 AM, shuah@kernel.org wrote:
From: Shuah Khan shuah@kernel.org
Media Device Allocator API to allows multiple drivers share a media device. Using this API, drivers can allocate a media device with the shared struct device as the key. Once the media device is allocated by a driver, other drivers can get a reference to it. The media device is released when all the references are released.
Signed-off-by: Shuah Khan shuah@kernel.org
Documentation/media/kapi/mc-core.rst | 37 ++++++++ drivers/media/Makefile | 3 +- drivers/media/media-dev-allocator.c | 132 +++++++++++++++++++++++++++ include/media/media-dev-allocator.h | 53 +++++++++++ 4 files changed, 224 insertions(+), 1 deletion(-) create mode 100644 drivers/media/media-dev-allocator.c create mode 100644 include/media/media-dev-allocator.h
diff --git a/Documentation/media/kapi/mc-core.rst b/Documentation/media/kapi/mc-core.rst index 0c05503eaf1f..d6f409598065 100644 --- a/Documentation/media/kapi/mc-core.rst +++ b/Documentation/media/kapi/mc-core.rst @@ -257,8 +257,45 @@ Subsystems should facilitate link validation by providing subsystem specific helper functions to provide easy access for commonly needed information, and in the end provide a way to use driver-specific callbacks.
+Media Controller Device Allocator API +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+When media device belongs to more than one driver, the shared media device
When -> When the
+is allocated with the shared struct device as the key for look ups.
+Shared media device should stay in registered state until the last driver
Shared -> The shared
+unregisters it. In addition, media device should be released when all the
media -> the media
+references are released. Each driver gets a reference to the media device +during probe, when it allocates the media device. If media device is already +allocated, allocate API bumps up the refcount and return the existing media
allocate -> the allocate return -> returns
+device. Driver puts the reference back from its disconnect routine when it
Driver -> The driver from -> in
+calls :c:func:`media_device_delete()`.
+Media device is unregistered and cleaned up from the kref put handler to
Media -> The media from -> in
+ensure that the media device stays in registered state until the last driver +unregisters the media device.
What happens if an application still has the media device open and you forcibly remove the last driver? I think it should be OK since the media_devnode struct isn't freed until the last open filehandle closes. But it is good to test this.
+**Driver Usage**
+Drivers should use the media-core routines to get register reference and
'get register reference'? Not sure what you meant to say.
+call :c:func:`media_device_delete()` routine to make sure the shared media +device delete is handled correctly.
+**driver probe:** +Call :c:func:`media_device_usb_allocate()` to allocate or get a reference +Call :c:func:`media_device_register()`, if media devnode isn't registered
+**driver disconnect:** +Call :c:func:`media_device_delete()` to free the media_device. Free'ing is
Free'ing -> Freeing
+handled by the kref put handler.
+API Definitions +^^^^^^^^^^^^^^^
.. kernel-doc:: include/media/media-device.h
.. kernel-doc:: include/media/media-devnode.h
.. kernel-doc:: include/media/media-entity.h
+.. kernel-doc:: include/media/media-dev-allocator.h diff --git a/drivers/media/Makefile b/drivers/media/Makefile index 594b462ddf0e..8608f0a41dca 100644 --- a/drivers/media/Makefile +++ b/drivers/media/Makefile @@ -3,7 +3,8 @@ # Makefile for the kernel multimedia device drivers. #
-media-objs := media-device.o media-devnode.o media-entity.o +media-objs := media-device.o media-devnode.o media-entity.o \
media-dev-allocator.o
Perhaps only add media-dev-allocator if CONFIG_USB is enabled?
# # I2C drivers should come before other drivers, otherwise they'll fail diff --git a/drivers/media/media-dev-allocator.c b/drivers/media/media-dev-allocator.c new file mode 100644 index 000000000000..262d1293dc13 --- /dev/null +++ b/drivers/media/media-dev-allocator.c @@ -0,0 +1,132 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/*
- media-dev-allocator.c - Media Controller Device Allocator API
- Copyright (c) 2018 Shuah Khan shuah@kernel.org
- Credits: Suggested by Laurent Pinchart laurent.pinchart@ideasonboard.com
- */
+/*
- This file adds a global refcounted Media Controller Device Instance API.
- A system wide global media device list is managed and each media device
- includes a kref count. The last put on the media device releases the media
- device instance.
- */
+#include <linux/kref.h> +#include <linux/module.h> +#include <linux/slab.h> +#include <linux/usb.h>
+#include <media/media-device.h>
+static LIST_HEAD(media_device_list); +static DEFINE_MUTEX(media_device_lock);
+struct media_device_instance {
- struct media_device mdev;
- struct module *owner;
- struct list_head list;
- struct kref refcount;
+};
+static inline struct media_device_instance * +to_media_device_instance(struct media_device *mdev) +{
- return container_of(mdev, struct media_device_instance, mdev);
+}
+static void media_device_instance_release(struct kref *kref) +{
- struct media_device_instance *mdi =
container_of(kref, struct media_device_instance, refcount);- dev_dbg(mdi->mdev.dev, "%s: mdev=%p\n", __func__, &mdi->mdev);
- mutex_lock(&media_device_lock);
Can't the lock be moved down to just before list_del? Or am I missing something?
- media_device_unregister(&mdi->mdev);
- media_device_cleanup(&mdi->mdev);
- list_del(&mdi->list);
- mutex_unlock(&media_device_lock);
- kfree(mdi);
+}
+/* Callers should hold media_device_lock when calling this function */ +static struct media_device *__media_device_get(struct device *dev,
char *module_name)
const char *
+{
- struct media_device_instance *mdi;
- list_for_each_entry(mdi, &media_device_list, list) {
if (mdi->mdev.dev != dev)continue;kref_get(&mdi->refcount);/* get module reference for the media_device owner */if (find_module(module_name) != mdi->owner &&!try_module_get(mdi->owner))dev_err(dev, "%s: try_module_get() error\n", __func__);dev_dbg(dev, "%s: get mdev=%p module_name %s\n",__func__, &mdi->mdev, module_name);return &mdi->mdev;- }
- mdi = kzalloc(sizeof(*mdi), GFP_KERNEL);
- if (!mdi)
return NULL;- mdi->owner = find_module(module_name);
- kref_init(&mdi->refcount);
- list_add_tail(&mdi->list, &media_device_list);
- dev_dbg(dev, "%s: alloc mdev=%p module_name %s\n", __func__,
&mdi->mdev, module_name);- return &mdi->mdev;
+}
+#if IS_ENABLED(CONFIG_USB) +struct media_device *media_device_usb_allocate(struct usb_device *udev,
char *module_name)
const char *
+{
- struct media_device *mdev;
- mutex_lock(&media_device_lock);
- mdev = __media_device_get(&udev->dev, module_name);
- if (!mdev) {
mutex_unlock(&media_device_lock);return ERR_PTR(-ENOMEM);- }
- /* check if media device is already initialized */
- if (!mdev->dev)
__media_device_usb_init(mdev, udev, udev->product,module_name);- mutex_unlock(&media_device_lock);
- return mdev;
+} +EXPORT_SYMBOL_GPL(media_device_usb_allocate); +#endif
+void media_device_delete(struct media_device *mdev, char *module_name) +{
- struct media_device_instance *mdi = to_media_device_instance(mdev);
- dev_dbg(mdi->mdev.dev, "%s: mdev=%p module_name %s\n",
__func__, &mdi->mdev, module_name);- mutex_lock(&media_device_lock);
- /* put module reference if media_device owner is not THIS_MODULE */
- if (mdi->owner != find_module(module_name)) {
module_put(mdi->owner);dev_dbg(mdi->mdev.dev,"%s decremented owner module reference\n", __func__);- }
- mutex_unlock(&media_device_lock);
- kref_put(&mdi->refcount, media_device_instance_release);
+} +EXPORT_SYMBOL_GPL(media_device_delete); diff --git a/include/media/media-dev-allocator.h b/include/media/media-dev-allocator.h new file mode 100644 index 000000000000..8fbadff2cef8 --- /dev/null +++ b/include/media/media-dev-allocator.h @@ -0,0 +1,53 @@ +/* SPDX-License-Identifier: GPL-2.0+ */ +/*
- media-dev-allocator.h - Media Controller Device Allocator API
- Copyright (c) 2018 Shuah Khan shuah@kernel.org
- Credits: Suggested by Laurent Pinchart laurent.pinchart@ideasonboard.com
- */
+/*
- This file adds a global ref-counted Media Controller Device Instance API.
- A system wide global media device list is managed and each media device
- includes a kref count. The last put on the media device releases the media
- device instance.
- */
+#ifndef _MEDIA_DEV_ALLOCTOR_H +#define _MEDIA_DEV_ALLOCTOR_H
+struct usb_device;
+#ifdef CONFIG_MEDIA_CONTROLLER
Perhaps change this to:
#if defined(CONFIG_MEDIA_CONTROLLER) && defined(CONFIG_USB)
Since for now this only makes sense for USB devices.
+/**
- media_device_usb_allocate() - Allocate and return struct &media device
- @udev: struct &usb_device pointer
- @module_name: should be filled with %KBUILD_MODNAME
- This interface should be called to allocate a Media Device when multiple
- drivers share usb_device and the media device. This interface allocates
- &media_device structure and calls media_device_usb_init() to initialize
- it.
- */
+struct media_device *media_device_usb_allocate(struct usb_device *udev,
char *module_name);+/**
- media_device_delete() - Release media device. Calls kref_put().
- @mdev: struct &media_device pointer
- @module_name: should be filled with %KBUILD_MODNAME
- This interface should be called to put Media Device Instance kref.
- */
+void media_device_delete(struct media_device *mdev, char *module_name); +#else +static inline struct media_device *media_device_usb_allocate(
struct usb_device *udev, char *module_name){ return NULL; }+static inline void media_device_delete(
struct media_device *mdev, char *module_name) { }+#endif /* CONFIG_MEDIA_CONTROLLER */ +#endif
Regards,
Hans