Messages in this thread | | | Subject | Re: [PATCH v12 1/5] media: Media Device Allocator API | From | shuah <> | Date | Wed, 27 Mar 2019 08:18:41 -0600 |
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On 3/27/19 7:55 AM, Hans Verkuil wrote: > On 3/27/19 2:45 PM, shuah wrote: >> 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. > > Ah, media-dev-allocator.c doesn't include media-dev-allocator.h. > > I suspect that that's the reason for the sparse warning. > >> >>> >>> 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. > > You can select MEDIA_CONTROLLER for au0828, but never MODULES. Selecting > MEDIA_CONTROLLER makes sense, I have no objection to that. > > What do you mean with 'no sharing happening'? You have to deal with > modules to make sure they are not unloaded, but other than that this > feature shouldn't depend on MODULES. Or am I missing something? > >>
You are right. It shouldn't depend on MODULES. The code that deals with modules so they don't get unloaded has dependency on MODULES, not all of it. I see the problem now.
I will update au0828 to select MEDIA_CONTROLLER and update the module logic and send v13. Maybe that is the lucky version :)
thanks, -- Shuah
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