xiaomi-sm8450/android_kernel_xiaomi_sm8450
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

media: Media Device Allocator API

Browse Source 
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>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
This commit is contained in:
Shuah Khan
2019-04-01 20:40:19 -04:00
committed by Mauro Carvalho Chehab
parent 33dfeb62e2
commit 6e1d824e7a
4 changed files with 245 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files

135
drivers/media/media-dev-allocator.c Normal file
View File

@@ -0,0 +1,135 @@
// SPDX-License-Identifier: GPL-2.0
/*
* media-dev-allocator.c - Media Controller Device Allocator API
*
* Copyright (c) 2019 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>
#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 *owner)
{
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 (owner != mdi->owner && !try_module_get(mdi->owner))
dev_err(dev,
"%s: module %s get owner reference error\n",
__func__, module_name);
else
dev_dbg(dev, "%s: module %s got owner reference\n",
__func__, module_name);
return &mdi->mdev;
}
mdi = kzalloc(sizeof(*mdi), GFP_KERNEL);
if (!mdi)
return NULL;
mdi->owner = owner;
kref_init(&mdi->refcount);
list_add_tail(&mdi->list, &media_device_list);
dev_dbg(dev, "%s: Allocated media device for owner %s\n",
__func__, module_name);
return &mdi->mdev;
}
struct media_device *media_device_usb_allocate(struct usb_device *udev,
const char *module_name,
struct module *owner)
{
struct media_device *mdev;
mutex_lock(&media_device_lock);
mdev = __media_device_get(&udev->dev, module_name, owner);
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 *owner)
{
struct media_device_instance *mdi = to_media_device_instance(mdev);
mutex_lock(&media_device_lock);
/* put module reference for the media_device owner */
if (mdi->owner != owner) {
module_put(mdi->owner);
dev_dbg(mdi->mdev.dev,
"%s: module %s put owner module reference\n",
__func__, module_name);
}
mutex_unlock(&media_device_lock);
kref_put(&mdi->refcount, media_device_instance_release);
}
EXPORT_SYMBOL_GPL(media_device_delete);