Hi Shuah,
On Thu, Jan 24, 2019 at 01:32:38PM -0700, Shuah Khan wrote:
Media Device Allocator API to allows multiple drivers share a media device. This API solves a very common use-case for media devices where one physical device (an USB stick) provides both audio and video. When such media device exposes a standard USB Audio class, a proprietary Video class, two or more independent drivers will share a single physical USB bridge. In such cases, it is necessary to coordinate access to the shared resource.
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.
Are there real, non-USB devices that could use the same API?
Signed-off-by: Shuah Khan shuah@kernel.org
Documentation/media/kapi/mc-core.rst | 41 ++++++++ drivers/media/Makefile | 4 + drivers/media/media-dev-allocator.c | 144 +++++++++++++++++++++++++++ include/media/media-dev-allocator.h | 53 ++++++++++ 4 files changed, 242 insertions(+) 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 0bcfeadbc52d..07f2a6a90af2 100644 --- a/Documentation/media/kapi/mc-core.rst +++ b/Documentation/media/kapi/mc-core.rst @@ -259,6 +259,45 @@ 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 the media device belongs to more than one driver, the shared media +device is allocated with the shared struct device as the key for look ups.
+The shared media device should stay in registered state until the last +driver unregisters it. In addition, the media device should be released when +all the 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, the allocate API bumps up the refcount and returns the +existing media device. The driver puts the reference back in its disconnect +routine when it calls :c:func:`media_device_delete()`.
+The media device is unregistered and cleaned up from the kref put handler to +ensure that the media device stays in registered state until the last driver +unregisters the media device.
+**Driver Usage**
+Drivers should use the appropriate media-core routines to manage the shared +media device life-time handling the two states: +1. allocate -> register -> delete +2. get reference to already registered device -> delete
+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. Freeing is +handled by the kref put handler.
+API Definitions +^^^^^^^^^^^^^^^
.. kernel-doc:: include/media/media-device.h
.. kernel-doc:: include/media/media-devnode.h @@ -266,3 +305,5 @@ in the end provide a way to use driver-specific callbacks. .. kernel-doc:: include/media/media-entity.h
.. kernel-doc:: include/media/media-request.h
+.. kernel-doc:: include/media/media-dev-allocator.h diff --git a/drivers/media/Makefile b/drivers/media/Makefile index 985d35ec6b29..1d7653318af6 100644 --- a/drivers/media/Makefile +++ b/drivers/media/Makefile @@ -6,6 +6,10 @@ media-objs := media-device.o media-devnode.o media-entity.o \ media-request.o
+ifeq ($(CONFIG_USB),y)
- media-objs += media-dev-allocator.o
+endif
# # I2C drivers should come before other drivers, otherwise they'll fail # when compiled as builtin drivers diff --git a/drivers/media/media-dev-allocator.c b/drivers/media/media-dev-allocator.c new file mode 100644 index 000000000000..4606456c1e86 --- /dev/null +++ b/drivers/media/media-dev-allocator.c @@ -0,0 +1,144 @@ +// SPDX-License-Identifier: GPL-2.0-or-later
GPL-2.0+
+/*
- 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);
- media_device_unregister(&mdi->mdev);
- media_device_cleanup(&mdi->mdev);
This is a problem, albeit not really more of a problem than it is in a driver. The refcounting changes can be made here instead. I'll take this into account in the media device refcounting series I'm planning to start working on again; would you be perhaps able to help testing with this device once I have patches in that shape? I have no access to the hardware.
- 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,
const char *module_name,struct module *modp)+{
- 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 (modp != 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 = modp;
- 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)
You already compile the file only if CONFIG_USB is enabled. I think you could remove this.
+struct media_device *media_device_usb_allocate(struct usb_device *udev,
const char *module_name)
I'd like to suggest working based on usb_interface instead of usb_device here: that object already exists and you can find out the device based on it. It seems all callers of this function already have the usb_interface around.
+{
- struct media_device *mdev;
- struct module *modptr;
- mutex_lock(&module_mutex);
- modptr = find_module(module_name);
- mutex_unlock(&module_mutex);
- mutex_lock(&media_device_lock);
- mdev = __media_device_get(&udev->dev, module_name, modptr);
- 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, const char *module_name)
Same here. The use of the module name seems a bit hackish to me, albeit I suppose it'd work, too.
+{
- struct media_device_instance *mdi = to_media_device_instance(mdev);
- struct module *modptr;
- dev_dbg(mdi->mdev.dev, "%s: mdev=%p module_name %s\n",
__func__, &mdi->mdev, module_name);- mutex_lock(&module_mutex);
- modptr = find_module(module_name);
- mutex_unlock(&module_mutex);
- mutex_lock(&media_device_lock);
- /* put module reference if media_device owner is not THIS_MODULE */
- if (mdi->owner != modptr) {
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..9164795e911c --- /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;
+#if defined(CONFIG_MEDIA_CONTROLLER) && defined(CONFIG_USB) +/**
- 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