From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,USER_AGENT_NEOMUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 58F2DC282C0 for ; Fri, 25 Jan 2019 15:39:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 20706218CD for ; Fri, 25 Jan 2019 15:39:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726921AbfAYPjU (ORCPT ); Fri, 25 Jan 2019 10:39:20 -0500 Received: from nblzone-211-213.nblnetworks.fi ([83.145.211.213]:49116 "EHLO hillosipuli.retiisi.org.uk" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726238AbfAYPjU (ORCPT ); Fri, 25 Jan 2019 10:39:20 -0500 Received: from valkosipuli.localdomain (valkosipuli.retiisi.org.uk [IPv6:2001:1bc8:1a6:d3d5::80:2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by hillosipuli.retiisi.org.uk (Postfix) with ESMTPS id ED6F1634C7B; Fri, 25 Jan 2019 17:38:42 +0200 (EET) Received: from sailus by valkosipuli.localdomain with local (Exim 4.89) (envelope-from ) id 1gn3Z5-0001Uk-W7; Fri, 25 Jan 2019 17:38:44 +0200 Date: Fri, 25 Jan 2019 17:38:43 +0200 From: Sakari Ailus To: Shuah Khan Cc: mchehab@kernel.org, perex@perex.cz, tiwai@suse.com, hverkuil@xs4all.nl, linux-media@vger.kernel.org, linux-kernel@vger.kernel.org, alsa-devel@alsa-project.org Subject: Re: [PATCH v10 1/4] media: Media Device Allocator API Message-ID: <20190125153843.onbq7uiwpjp3b2y7@valkosipuli.retiisi.org.uk> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > --- > 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 > + * > + * 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 > + > +#include > + > +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 > + * > + * 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; > + > +#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 -- Regards, Sakari Ailus