Messages in this thread | | | Subject | Re: [PATCH v12 1/5] media: Media Device Allocator API | From | shuah <> | Date | Wed, 27 Mar 2019 07:45:19 -0600 |
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Hi Hans,
On 3/27/19 4:37 AM, Hans Verkuil wrote: > Hi Shuah, > > Some comments at the end. I suspect you still have to do more work :-(
I am okay with doing more work. I am expecting it since, I am not happy with the config options that are in play. More on this below.
> > On 3/27/19 3:24 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 | 142 +++++++++++++++++++++++++++ >> include/media/media-dev-allocator.h | 54 ++++++++++ >> 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..20b488067ec2 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 ($(CONFIG_USB),y) >> + ifeq ($(CONFIG_MODULES),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..a37515254009 >> --- /dev/null >> +++ b/drivers/media/media-dev-allocator.c >> @@ -0,0 +1,142 @@ >> +// SPDX-License-Identifier: 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); >> + >> + 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; >> +} >> + >> +struct media_device *media_device_usb_allocate(struct usb_device *udev, >> + const char *module_name) >> +{ >> + 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); >> + >> +void media_device_delete(struct media_device *mdev, const char *module_name) >> +{ >> + 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..69aee9a4b4c1 >> --- /dev/null >> +++ b/include/media/media-dev-allocator.h >> @@ -0,0 +1,54 @@ >> +/* 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) && \ >> + defined(CONFIG_MODULES) >> +/** >> + * 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 && CONFIG_USB && CONFIG_MODULES */ > > I am still getting sparse warnings: > > drivers/media/media-dev-allocator.c /home/hans/work/build/media-git/drivers/media/media-dev-allocator.c:94:21: warning: symbol 'media_device_usb_allocate' was not declared. Should it be static? > drivers/media/media-dev-allocator.c /home/hans/work/build/media-git/drivers/media/media-dev-allocator.c:120:6: warning: symbol 'media_device_delete' was not declared. Should it be static? > drivers/media/media-dev-allocator.c:94:22: warning: no previous prototype for 'media_device_usb_allocate' [-Wmissing-prototypes] > drivers/media/media-dev-allocator.c:120:6: warning: no previous prototype for 'media_device_delete' [-Wmissing-prototypes]
I didn't see the warns - maybe I have to upgrade to the latest gcc.
> > This makes sense since if the #if above evaluates to 0, then the > static inlines are used. But in media-dev-allocator.c these functions > are still present without a corresponding prototype. > > You likely need a similar #if in media-dev-allocator.c. > > Have you tested this if CONFIG_MODULES is not set? Does au0828 still work > w.r.t. sharing the shared resource? Has the driver been tested when MEDIA_CONTROLLER > is not set? Should au0828 select MEDIA_CONTROLLER explicitly perhaps?
Unfortunately without MEDIA_CONTROLLER and CONFIG_MODULES, no sharing happening. The only way to ensure sharing in all cases, is selecting MEDIA_CONTROLLER and MODULES in au0828 and that will make sure snd-usb-audio enables SND_USB_AUDIO_USE_MEDIA_CONTROLLER and all of the sharing logic works.
> > My main concern is that it looks like au0828's probe() will now fail if MODULES is > not set. >
Agreed. At the moment, we have too many config options in play even before this work. Maybe it is time au0828 selected MEDIA_CONTROLLER and CONFIG_MODULES - this will make sure all of this works.
I was hoping to start the config option discussion, so we can decide on a set of options to select from these drivers.
thanks, -- Shuah
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