Hi Shuah,
Thanks! This looks much better.
I have a few remaining trivial comments:
On 3/29/19 1:04 AM, 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.
Signed-off-by: Shuah Khan shuah@kernel.org
Documentation/media/kapi/mc-core.rst | 41 +++++++++ drivers/media/Makefile | 6 ++ drivers/media/media-dev-allocator.c | 133 +++++++++++++++++++++++++++ include/media/media-dev-allocator.h | 63 +++++++++++++ 4 files changed, 243 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 f930725e0d6b..05bba0b61748 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..4a330d0e5e40 100644 --- a/drivers/media/Makefile +++ b/drivers/media/Makefile @@ -6,6 +6,12 @@ media-objs := media-device.o media-devnode.o media-entity.o \ media-request.o
+ifeq ($(CONFIG_MEDIA_CONTROLLER),y)
- ifeq ($(CONFIG_USB),y)
media-objs += media-dev-allocator.o- endif
+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..8f4ddc4d13f5 --- /dev/null +++ b/drivers/media/media-dev-allocator.c @@ -0,0 +1,133 @@ +// SPDX-License-Identifier: GPL-2.0 +/*
- media-dev-allocator.c - Media Controller Device Allocator API
- Copyright (c) 2018 Shuah Khan shuah@kernel.org
Update copyright year to 2019? (check all sources for this)
- 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> +#include <media/media-dev-allocator.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: releasing Media Device\n", __func__);
- mutex_lock(&media_device_lock);
- 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,
const char *module_name,struct module *modp)
You use various names for the module argument: module, modp, modptr. Why not always call it 'owner', since that's what it is, and that's what it is called in struct media_device_instance?
+{
- struct media_device_instance *mdi;
- list_for_each_entry(mdi, &media_device_list, list) {
Please drop this empty line.
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__);
I recommend that you show module_name in the message, and add an 'else' after dev_err, otherwise you get both the dev_err and dev_dbg on error.
dev_dbg(dev, "%s: get module_name %s\n",__func__, module_name);
I think this can fit on one line. Also, perhaps the text of the message should be a bit clearer?
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 module_name %s\n", __func__, module_name);
This message can be a bit more clearer as well.
- return &mdi->mdev;
+}
+struct media_device *media_device_usb_allocate(struct usb_device *udev,
const char *module_name,struct module *modptr)+{
- struct media_device *mdev;
- 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);
+void media_device_delete(struct media_device *mdev, const char *module_name,
struct module *modptr)+{
- struct media_device_instance *mdi = to_media_device_instance(mdev);
- dev_dbg(mdi->mdev.dev, "%s: module_name %s\n", __func__, module_name);
- mutex_lock(&media_device_lock);
- /* put module reference if media_device owner is not modptr */
- 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..73d8013c8ab5 --- /dev/null +++ b/include/media/media-dev-allocator.h @@ -0,0 +1,63 @@ +/* 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
ALLOCTOR -> ALLOCATOR
+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
- @module: struct module pointer %THIS_MODULE for the driver.
%THIS_MODULE is null for a built-in driver.
It is safe even when %THIS_MODULE is null.
- 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,
const char *module_name,struct module *module);+/**
- media_device_delete() - Release media device. Calls kref_put().
- @mdev: struct &media_device pointer
- @module_name: should be filled with %KBUILD_MODNAME
- @module: struct module pointer %THIS_MODULE for the driver.
%THIS_MODULE is null for a built-in driver.
It is safe even when %THIS_MODULE is null.
- This interface should be called to put Media Device Instance kref.
- */
+void media_device_delete(struct media_device *mdev, const char *module_name,
struct module *module);+#else +static inline struct media_device *media_device_usb_allocate(
struct usb_device *udev, const char *module_name,struct module *module){ return NULL; }+static inline void media_device_delete(
struct media_device *mdev, const char *module_name,struct module *module) { }
In this header 'module' is used as the name for struct module *. Here too I recommend changing it to 'owner'.
+#endif /* CONFIG_MEDIA_CONTROLLER && CONFIG_USB */ +#endif
Regards,
Hans