Messages in this thread | | | Subject | Re: [RFC PATCH v8 1/4] media: Media Device Allocator API | From | shuah <> | Date | Thu, 6 Dec 2018 08:27:19 -0700 |
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Hi Hans,
On 11/20/18 4:20 AM, Hans Verkuil wrote: > On 11/02/2018 01:31 AM, shuah@kernel.org wrote: >> From: Shuah Khan <shuah@kernel.org> >> >> Media Device Allocator API to allows multiple drivers share a media device. >> 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>
Thanks for catching the documentation corrections. Fixed them all and working on the next revision of the patch.
>> --- >> Documentation/media/kapi/mc-core.rst | 37 ++++++++ >> drivers/media/Makefile | 3 +- >> drivers/media/media-dev-allocator.c | 132 +++++++++++++++++++++++++++ >> include/media/media-dev-allocator.h | 53 +++++++++++ >> 4 files changed, 224 insertions(+), 1 deletion(-) >> 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 0c05503eaf1f..d6f409598065 100644 >> --- a/Documentation/media/kapi/mc-core.rst >> +++ b/Documentation/media/kapi/mc-core.rst >> @@ -257,8 +257,45 @@ 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 media device belongs to more than one driver, the shared media device > > When -> When the > >> +is allocated with the shared struct device as the key for look ups. >> + >> +Shared media device should stay in registered state until the last driver > > Shared -> The shared > >> +unregisters it. In addition, media device should be released when all the > > media -> the media > >> +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, allocate API bumps up the refcount and return the existing media > > allocate -> the allocate > return -> returns > >> +device. Driver puts the reference back from its disconnect routine when it > > Driver -> The driver > from -> in > >> +calls :c:func:`media_device_delete()`. >> + >> +Media device is unregistered and cleaned up from the kref put handler to > > Media -> The media > from -> in > >> +ensure that the media device stays in registered state until the last driver >> +unregisters the media device. > > What happens if an application still has the media device open and you forcibly > remove the last driver? I think it should be OK since the media_devnode struct > isn't freed until the last open filehandle closes. But it is good to test this. > >> + >> +**Driver Usage** >> + >> +Drivers should use the media-core routines to get register reference and > > 'get register reference'? Not sure what you meant to say. > >> +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. Free'ing is > > Free'ing -> Freeing > >> +handled by the kref put handler. >> + >> +API Definitions >> +^^^^^^^^^^^^^^^ >> + >> .. kernel-doc:: include/media/media-device.h >> >> .. kernel-doc:: include/media/media-devnode.h >> >> .. kernel-doc:: include/media/media-entity.h >> + >> +.. kernel-doc:: include/media/media-dev-allocator.h >> diff --git a/drivers/media/Makefile b/drivers/media/Makefile >> index 594b462ddf0e..8608f0a41dca 100644 >> --- a/drivers/media/Makefile >> +++ b/drivers/media/Makefile >> @@ -3,7 +3,8 @@ >> # Makefile for the kernel multimedia device drivers. >> # >> >> -media-objs := media-device.o media-devnode.o media-entity.o >> +media-objs := media-device.o media-devnode.o media-entity.o \ >> + media-dev-allocator.o > > Perhaps only add media-dev-allocator if CONFIG_USB is enabled? > >> >> # >> # I2C drivers should come before other drivers, otherwise they'll fail >> diff --git a/drivers/media/media-dev-allocator.c b/drivers/media/media-dev-allocator.c >> new file mode 100644 >> index 000000000000..262d1293dc13 >> --- /dev/null >> +++ b/drivers/media/media-dev-allocator.c >> @@ -0,0 +1,132 @@ >> +// 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); > > Can't the lock be moved down to just before list_del? Or am I missing something? >
The lock needs to be held while media_device_unregister() and media_device_cleanup() to avoid races in the unregister path if two drivers call media_device_delete().
>> + >> + 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, >> + char *module_name) > > const char *
Thanks fixed all of these.
I am running final tests and will send the next version this week.
thanks, -- Shuah
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