From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754767AbcEWL0M (ORCPT ); Mon, 23 May 2016 07:26:12 -0400 Received: from lb3-smtp-cloud6.xs4all.net ([194.109.24.31]:45566 "EHLO lb3-smtp-cloud6.xs4all.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753562AbcEWL0K (ORCPT ); Mon, 23 May 2016 07:26:10 -0400 Subject: Re: [PATCH 1/3] media: Media Device Allocator API To: Shuah Khan , mchehab@osg.samsung.com, laurent.pinchart@ideasonboard.com, sakari.ailus@iki.fi, hans.verkuil@cisco.com, chehabrafael@gmail.com, javier@osg.samsung.com, inki.dae@samsung.com, g.liakhovetski@gmx.de, jh1009.sung@samsung.com References: Cc: linux-media@vger.kernel.org, linux-kernel@vger.kernel.org From: Hans Verkuil Message-ID: <5742E8CC.2060806@xs4all.nl> Date: Mon, 23 May 2016 13:26:04 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Icedove/38.7.2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Shuah, Some comments below: On 05/13/2016 07:09 PM, Shuah Khan wrote: > 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 > --- > drivers/media/Makefile | 3 +- > drivers/media/media-dev-allocator.c | 139 ++++++++++++++++++++++++++++++++++++ > include/media/media-dev-allocator.h | 118 ++++++++++++++++++++++++++++++ > 3 files changed, 259 insertions(+), 1 deletion(-) > create mode 100644 drivers/media/media-dev-allocator.c > create mode 100644 include/media/media-dev-allocator.h > > diff --git a/drivers/media/Makefile b/drivers/media/Makefile > index e608bbc..b08f091 100644 > --- a/drivers/media/Makefile > +++ b/drivers/media/Makefile > @@ -2,7 +2,8 @@ > # 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 > > # > # 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 0000000..b49ab55 > --- /dev/null > +++ b/drivers/media/media-dev-allocator.c > @@ -0,0 +1,139 @@ > +/* > + * media-dev-allocator.c - Media Controller Device Allocator API > + * > + * Copyright (c) 2016 Shuah Khan > + * Copyright (c) 2016 Samsung Electronics Co., Ltd. > + * > + * This file is released under the GPLv2. > + * Credits: Suggested by Laurent Pinchart > + */ > + > +/* > + * 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 > +#include > +#include > +#include > + > +static LIST_HEAD(media_device_list); > +static DEFINE_MUTEX(media_device_lock); > + > +struct media_device_instance { > + struct media_device mdev; > + struct list_head list; > + struct device *dev; > + 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); > +} > + > +static struct media_device *__media_device_get(struct device *dev, > + bool allocate) > +{ > + struct media_device_instance *mdi; > + > + mutex_lock(&media_device_lock); > + > + list_for_each_entry(mdi, &media_device_list, list) { > + if (mdi->dev == dev) { > + kref_get(&mdi->refcount); > + dev_dbg(dev, "%s: get mdev=%p\n", > + __func__, &mdi->mdev); > + goto done; > + } > + } > + > + if (!allocate) { > + mdi = NULL; > + goto done; > + } > + > + mdi = kzalloc(sizeof(*mdi), GFP_KERNEL); > + if (!mdi) > + goto done; > + > + mdi->dev = dev; > + kref_init(&mdi->refcount); > + list_add_tail(&mdi->list, &media_device_list); > + > + dev_dbg(dev, "%s: alloc mdev=%p\n", __func__, &mdi->mdev); > + > +done: > + mutex_unlock(&media_device_lock); > + > + return mdi ? &mdi->mdev : NULL; > +} > + > +struct media_device *media_device_allocate(struct device *dev) > +{ > + dev_dbg(dev, "%s\n", __func__); > + return __media_device_get(dev, true); > +} > +EXPORT_SYMBOL_GPL(media_device_allocate); Do we need this function? Whenever a media device is allocated, you also need to initialize the media device with the media_device_lock held (as happens below in media_device_usb_allocate). You can't really use this function standalone as far as I can see. An alternative might be to pass a callback function with media_device_allocate that initialized the media device. That would ensure that there are no race conditions since media_device_allocate can lock media_device_lock before calling the callback. > + > +struct media_device *media_device_usb_allocate(struct usb_device *udev, > + char *driver_name) > +{ > + struct media_device *mdev; > + > + mdev = media_device_allocate(&udev->dev); > + if (!mdev) > + return ERR_PTR(-ENOMEM); > + > + /* check if media device is already initialized */ > + mutex_lock(&media_device_lock); > + if (!mdev->dev) > + __media_device_usb_init(mdev, udev, udev->product, > + driver_name); > + mutex_unlock(&media_device_lock); > + > + return mdev; > +} > +EXPORT_SYMBOL_GPL(media_device_usb_allocate); > + > +/* don't allocate - get reference if one is found */ > +struct media_device *media_device_get(struct media_device *mdev) > +{ > + struct media_device_instance *mdi = to_media_device_instance(mdev); > + > + dev_dbg(mdi->mdev.dev, "%s: mdev=%p\n", __func__, &mdi->mdev); > + return __media_device_get(mdi->dev, false); > +} > +EXPORT_SYMBOL_GPL(media_device_get); Do we need this anywhere? It makes no sense to call this standalone, at least, not that I can see. You just have different drivers that all call media_device_usb_allocate, and they also call media_device_put when they are done with it. See also my comments for the next patch. > + > +void media_device_put(struct media_device *mdev) > +{ > + struct media_device_instance *mdi = to_media_device_instance(mdev); > + > + dev_dbg(mdi->mdev.dev, "%s: mdev=%p\n", __func__, &mdi->mdev); > + kref_put(&mdi->refcount, media_device_instance_release); > +} > +EXPORT_SYMBOL_GPL(media_device_put); > diff --git a/include/media/media-dev-allocator.h b/include/media/media-dev-allocator.h > new file mode 100644 > index 0000000..a63dfc6 > --- /dev/null > +++ b/include/media/media-dev-allocator.h > @@ -0,0 +1,118 @@ > +/* > + * media-dev-allocator.h - Media Controller Device Allocator API > + * > + * Copyright (c) 2016 Shuah Khan > + * Copyright (c) 2016 Samsung Electronics Co., Ltd. > + * > + * This file is released under the GPLv2. > + * Credits: Suggested by Laurent Pinchart > + */ > + > +/* > + * 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; > + > +#ifdef CONFIG_MEDIA_CONTROLLER > +/** > + * DOC: Media Controller Device Allocator API > + * > + * When 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. > + * > + * Shared media device should stay in registered state until the last driver > + * unregisters it. In addition, 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, allocate API bumps up the refcount and return the existing media > + * device. Driver puts the reference back from its disconnect routine when it > + * calls media_device_unregister_put(). > + * > + * 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. > + * > + * Media Device can be in any the following states: > + * > + * - Allocated I don't think this is a real state. It's either unregistered or allocated and registered. Just 'allocated' doesn't really make sense. This ties in to my comment about media_device_allocate(). > + * - Registered (could be tied to more than one driver) > + * - Unregistered and released in the kref put handler. I would probably drop these 5 lines altogether. > + * > + * Driver Usage: > + * > + * Drivers should use the media-core routines to get register reference and > + * use the media_device_unregister_put() routine to make sure the shared > + * media device delete is handled correctly. > + * > + * driver probe: > + * Call media_device_usb_allocate() to allocate or get a reference > + * Call media_device_register(), if media devnode isn't registered > + * > + * driver disconnect: > + * Call media_device_unregister_put() to put the reference. There is no media_device_unregister_put() (yet). That should be in the next patch. > + * > + */ > + > +/** > + * media_device_usb_allocate() - Allocate and return media device > + * > + * @udev - struct usb_device pointer > + * @driver_name > + * > + * 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 and calls media_device_usb_init() to initialize it. > + * > + */ > +struct media_device *media_device_usb_allocate(struct usb_device *udev, > + char *driver_name); > +/** > + * media_device_allocate() - Allocate and return global media device > + * > + * @dev - struct device pointer > + * > + * This interface should be called to allocate media device. A new media > + * device instance is created and added to the system wide media device > + * instance list. If media device instance exists, media_device_allocate() > + * increments the reference count and returns the media device. When more > + * than one driver control the media device, the first driver to probe will > + * allocate and the second driver when it calls media_device_allocate(), > + * it will get a reference. > + * > + */ > +struct media_device *media_device_allocate(struct device *dev); > +/** > + * media_device_get() - Get reference to a registered media device. > + * > + * @mdev - struct media_device pointer > + * > + * This interface should be called to get a reference to an allocated media > + * device. > + */ > +struct media_device *media_device_get(struct media_device *mdev); > +/** > + * media_device_put() - Release media device. Calls kref_put(). > + * > + * @mdev - struct media_device pointer > + * > + * This interface should be called to put Media Device Instance kref. > + */ > +void media_device_put(struct media_device *mdev); > +#else > +static inline struct media_device *media_device_usb_allocate( > + struct usb_device *udev, char *driver_name) > + { return NULL; } > +static inline struct media_device *media_device_allocate(struct device *dev) > + { return NULL; } > +static inline struct media_device *media_device_get(struct media_device *mdev) > + { return NULL; } > +static inline void media_device_put(struct media_device *mdev) { } > +#endif /* CONFIG_MEDIA_CONTROLLER */ > +#endif > Regards, Hans