forked from mirrors/linux
6e1d824e7a
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>
135 lines
3.5 KiB
C
135 lines
3.5 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* media-dev-allocator.c - Media Controller Device Allocator API
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*
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* Copyright (c) 2019 Shuah Khan <shuah@kernel.org>
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*
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* Credits: Suggested by Laurent Pinchart <laurent.pinchart@ideasonboard.com>
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*/
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/*
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* This file adds a global refcounted Media Controller Device Instance API.
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* A system wide global media device list is managed and each media device
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* includes a kref count. The last put on the media device releases the media
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* device instance.
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*
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*/
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#include <linux/kref.h>
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#include <linux/module.h>
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#include <linux/slab.h>
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#include <linux/usb.h>
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#include <media/media-device.h>
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#include <media/media-dev-allocator.h>
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static LIST_HEAD(media_device_list);
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static DEFINE_MUTEX(media_device_lock);
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struct media_device_instance {
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struct media_device mdev;
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struct module *owner;
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struct list_head list;
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struct kref refcount;
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};
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static inline struct media_device_instance *
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to_media_device_instance(struct media_device *mdev)
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{
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return container_of(mdev, struct media_device_instance, mdev);
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}
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static void media_device_instance_release(struct kref *kref)
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{
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struct media_device_instance *mdi =
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container_of(kref, struct media_device_instance, refcount);
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dev_dbg(mdi->mdev.dev, "%s: releasing Media Device\n", __func__);
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mutex_lock(&media_device_lock);
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media_device_unregister(&mdi->mdev);
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media_device_cleanup(&mdi->mdev);
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list_del(&mdi->list);
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mutex_unlock(&media_device_lock);
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kfree(mdi);
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}
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/* Callers should hold media_device_lock when calling this function */
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static struct media_device *__media_device_get(struct device *dev,
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const char *module_name,
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struct module *owner)
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{
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struct media_device_instance *mdi;
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list_for_each_entry(mdi, &media_device_list, list) {
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if (mdi->mdev.dev != dev)
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continue;
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kref_get(&mdi->refcount);
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/* get module reference for the media_device owner */
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if (owner != mdi->owner && !try_module_get(mdi->owner))
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dev_err(dev,
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"%s: module %s get owner reference error\n",
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__func__, module_name);
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else
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dev_dbg(dev, "%s: module %s got owner reference\n",
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__func__, module_name);
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return &mdi->mdev;
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}
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mdi = kzalloc(sizeof(*mdi), GFP_KERNEL);
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if (!mdi)
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return NULL;
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mdi->owner = owner;
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kref_init(&mdi->refcount);
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list_add_tail(&mdi->list, &media_device_list);
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dev_dbg(dev, "%s: Allocated media device for owner %s\n",
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__func__, module_name);
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return &mdi->mdev;
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}
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struct media_device *media_device_usb_allocate(struct usb_device *udev,
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const char *module_name,
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struct module *owner)
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{
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struct media_device *mdev;
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mutex_lock(&media_device_lock);
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mdev = __media_device_get(&udev->dev, module_name, owner);
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if (!mdev) {
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mutex_unlock(&media_device_lock);
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return ERR_PTR(-ENOMEM);
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}
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/* check if media device is already initialized */
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if (!mdev->dev)
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__media_device_usb_init(mdev, udev, udev->product,
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module_name);
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mutex_unlock(&media_device_lock);
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return mdev;
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}
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EXPORT_SYMBOL_GPL(media_device_usb_allocate);
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void media_device_delete(struct media_device *mdev, const char *module_name,
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struct module *owner)
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{
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struct media_device_instance *mdi = to_media_device_instance(mdev);
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mutex_lock(&media_device_lock);
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/* put module reference for the media_device owner */
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if (mdi->owner != owner) {
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module_put(mdi->owner);
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dev_dbg(mdi->mdev.dev,
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"%s: module %s put owner module reference\n",
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__func__, module_name);
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}
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mutex_unlock(&media_device_lock);
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kref_put(&mdi->refcount, media_device_instance_release);
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}
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EXPORT_SYMBOL_GPL(media_device_delete);
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