| Message ID | df3aae79629e5c0ab5a57dfaf5e2d815a134cd2d.1548360791.git.shuah@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Media Device Allocator API | expand |
Hi Shuah, On Thu, Jan 24, 2019 at 01:32:38PM -0700, 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. Are there real, non-USB devices that could use the same API? > > Signed-off-by: Shuah Khan <shuah@kernel.org> > --- > Documentation/media/kapi/mc-core.rst | 41 ++++++++ > drivers/media/Makefile | 4 + > drivers/media/media-dev-allocator.c | 144 +++++++++++++++++++++++++++ > include/media/media-dev-allocator.h | 53 ++++++++++ > 4 files changed, 242 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 0bcfeadbc52d..07f2a6a90af2 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..1d7653318af6 100644 > --- a/drivers/media/Makefile > +++ b/drivers/media/Makefile > @@ -6,6 +6,10 @@ > media-objs := media-device.o media-devnode.o media-entity.o \ > media-request.o > > +ifeq ($(CONFIG_USB),y) > + media-objs += media-dev-allocator.o > +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..4606456c1e86 > --- /dev/null > +++ b/drivers/media/media-dev-allocator.c > @@ -0,0 +1,144 @@ > +// SPDX-License-Identifier: GPL-2.0-or-later 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); This is a problem, albeit not really more of a problem than it is in a driver. The refcounting changes can be made here instead. I'll take this into account in the media device refcounting series I'm planning to start working on again; would you be perhaps able to help testing with this device once I have patches in that shape? I have no access to the hardware. > + > + 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; > +} > + > +#if IS_ENABLED(CONFIG_USB) You already compile the file only if CONFIG_USB is enabled. I think you could remove this. > +struct media_device *media_device_usb_allocate(struct usb_device *udev, > + const char *module_name) I'd like to suggest working based on usb_interface instead of usb_device here: that object already exists and you can find out the device based on it. It seems all callers of this function already have the usb_interface around. > +{ > + 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); > +#endif > + > +void media_device_delete(struct media_device *mdev, const char *module_name) Same here. The use of the module name seems a bit hackish to me, albeit I suppose it'd work, too. > +{ > + 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..9164795e911c > --- /dev/null > +++ b/include/media/media-dev-allocator.h > @@ -0,0 +1,53 @@ > +/* 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) > +/** > + * 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 */ > +#endif
Hi Sakari, On 1/25/19 8:38 AM, Sakari Ailus wrote: > Hi Shuah, > > On Thu, Jan 24, 2019 at 01:32:38PM -0700, 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. > > Are there real, non-USB devices that could use the same API? > There might be. I don't have any to test. This patch is restricted to USB at the moment. >> >> Signed-off-by: Shuah Khan <shuah@kernel.org> >> --- >> Documentation/media/kapi/mc-core.rst | 41 ++++++++ >> drivers/media/Makefile | 4 + >> drivers/media/media-dev-allocator.c | 144 +++++++++++++++++++++++++++ >> include/media/media-dev-allocator.h | 53 ++++++++++ >> 4 files changed, 242 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 0bcfeadbc52d..07f2a6a90af2 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..1d7653318af6 100644 >> --- a/drivers/media/Makefile >> +++ b/drivers/media/Makefile >> @@ -6,6 +6,10 @@ >> media-objs := media-device.o media-devnode.o media-entity.o \ >> media-request.o >> >> +ifeq ($(CONFIG_USB),y) >> + media-objs += media-dev-allocator.o >> +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..4606456c1e86 >> --- /dev/null >> +++ b/drivers/media/media-dev-allocator.c >> @@ -0,0 +1,144 @@ >> +// SPDX-License-Identifier: GPL-2.0-or-later > > GPL-2.0+ > I would like to address this in a follow-on patch instead of re-doing the series again. Hope that is okay. >> +/* >> + * 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); > > This is a problem, albeit not really more of a problem than it is in a > driver. Okay good to know that it can be addressed in your media device refcounting series. The refcounting changes can be made here instead. I'll take this > into account in the media device refcounting series I'm planning to start > working on again; would you be perhaps able to help testing with this > device once I have patches in that shape? I have no access to the hardware. > Absolutely. I will be happy to help you with testing on the same hardware, I used for this series. >> + >> + 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; >> +} >> + >> +#if IS_ENABLED(CONFIG_USB) > > You already compile the file only if CONFIG_USB is enabled. I think you > could remove this. > >> +struct media_device *media_device_usb_allocate(struct usb_device *udev, >> + const char *module_name) > > I'd like to suggest working based on usb_interface instead of usb_device > here: that object already exists and you can find out the device based on > it. It seems all callers of this function already have the usb_interface > around. > Is there an advantage to using interface instead of the parent device? Is there a problem doing it this way? >> +{ >> + 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); >> +#endif >> + >> +void media_device_delete(struct media_device *mdev, const char *module_name) > > Same here. The use of the module name seems a bit hackish to me, albeit I > suppose it'd work, too. > What is hackish about it? I found it very useful to use it in debug and error messages that are user-friendly. thanks, -- Shuah
diff --git a/Documentation/media/kapi/mc-core.rst b/Documentation/media/kapi/mc-core.rst index 0bcfeadbc52d..07f2a6a90af2 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..1d7653318af6 100644 --- a/drivers/media/Makefile +++ b/drivers/media/Makefile @@ -6,6 +6,10 @@ media-objs := media-device.o media-devnode.o media-entity.o \ media-request.o +ifeq ($(CONFIG_USB),y) + media-objs += media-dev-allocator.o +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..4606456c1e86 --- /dev/null +++ b/drivers/media/media-dev-allocator.c @@ -0,0 +1,144 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * 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; +} + +#if IS_ENABLED(CONFIG_USB) +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); +#endif + +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..9164795e911c --- /dev/null +++ b/include/media/media-dev-allocator.h @@ -0,0 +1,53 @@ +/* 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) +/** + * 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 */ +#endif
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 | 4 + drivers/media/media-dev-allocator.c | 144 +++++++++++++++++++++++++++ include/media/media-dev-allocator.h | 53 ++++++++++ 4 files changed, 242 insertions(+) create mode 100644 drivers/media/media-dev-allocator.c create mode 100644 include/media/media-dev-allocator.h