From patchwork Mon Jun 17 06:04:10 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Guennadi Liakhovetski X-Patchwork-Id: 2730561 Return-Path: X-Original-To: patchwork-linux-media@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork2.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.19.201]) by patchwork2.web.kernel.org (Postfix) with ESMTP id 15E9EC0AB1 for ; Mon, 17 Jun 2013 06:05:01 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id D0ECE2015B for ; Mon, 17 Jun 2013 06:04:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9308A20159 for ; Mon, 17 Jun 2013 06:04:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750937Ab3FQGEp (ORCPT ); Mon, 17 Jun 2013 02:04:45 -0400 Received: from moutng.kundenserver.de ([212.227.17.10]:64273 "EHLO moutng.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750750Ab3FQGEo (ORCPT ); Mon, 17 Jun 2013 02:04:44 -0400 Received: from axis700.grange (dslb-178-001-146-073.pools.arcor-ip.net [178.1.146.73]) by mrelayeu.kundenserver.de (node=mreu3) with ESMTP (Nemesis) id 0M5mBh-1UQUdf3mDB-00xsUB; Mon, 17 Jun 2013 08:04:11 +0200 Received: by axis700.grange (Postfix, from userid 1000) id 615E640BB4; Mon, 17 Jun 2013 08:04:10 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by axis700.grange (Postfix) with ESMTP id 5E34240BB3; Mon, 17 Jun 2013 08:04:10 +0200 (CEST) Date: Mon, 17 Jun 2013 08:04:10 +0200 (CEST) From: Guennadi Liakhovetski X-X-Sender: lyakh@axis700.grange To: Linux Media Mailing List cc: Laurent Pinchart , Sylwester Nawrocki , Magnus Damm , Sakari Ailus , Prabhakar Lad , Sascha Hauer , Hans Verkuil Subject: [PATCH] V4L2: add documentation for V4L2 clock helpers and asynchronous probing Message-ID: MIME-Version: 1.0 X-Provags-ID: V02:K0:xzbPSEEQAZgrqe2ZoPjM86HewSG6fURP+BwkqihtNVe L8+O5xcxXo2AJuoQ/Hl2Ai6mGhsyZTNjDWbMr8XiuZ4on0IngW 0Loo8rxWEHeRguuaT9NQ5mp4moqFEWQRhVJcjyqG2bAQLV44/M v34mIbKPx+1PZvhSbM+BRthkurxZSJr3TE+0X7uYOD0DeNkZCb EdWAThuEzRl4vBaJjDv6NfsyMKYM1MP+2vpZT8Qw31KRcGdHP/ winKLcuHhGL1TMeRvMLKF1oFjyytGVxhE5VnqucWZydzyRHQ40 50rIQfvGFFPMukrfEfGLoM0vbvVNt7cClv57p8tnXPMjZlBRv/ qAy0apvu7TZxRyzqsFcJzLFVr6ah6uxjR7PtzEKRY/COy9XjpJ ezO10mSPM74xQ== Sender: linux-media-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org X-Spam-Status: No, score=-8.0 required=5.0 tests=BAYES_00,FREEMAIL_FROM, RCVD_IN_DNSWL_HI, RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=ham version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Add documentation for the V4L2 clock and V4L2 asynchronous probing APIs to v4l2-framework.txt. Signed-off-by: Guennadi Liakhovetski Reviewed-by: Lad, Prabhakar --- Hopefully we can commit the actual patches now, while we refine the documentation. Documentation/video4linux/v4l2-framework.txt | 62 +++++++++++++++++++++++++- 1 files changed, 60 insertions(+), 2 deletions(-) diff --git a/Documentation/video4linux/v4l2-framework.txt b/Documentation/video4linux/v4l2-framework.txt index a300b28..159a83a 100644 --- a/Documentation/video4linux/v4l2-framework.txt +++ b/Documentation/video4linux/v4l2-framework.txt @@ -326,8 +326,27 @@ that width, height and the media bus pixel code are equal on both source and sink of the link. Subdev drivers are also free to use this function to perform the checks mentioned above in addition to their own checks. -A device (bridge) driver needs to register the v4l2_subdev with the -v4l2_device: +There are currently two ways to register subdevices with the V4L2 core. The +first (traditional) possibility is to have subdevices registered by bridge +drivers. This can be done, when the bridge driver has the complete information +about subdevices, connected to it and knows exactly when to register them. This +is typically the case for internal subdevices, like video data processing units +within SoCs or complex pluggable boards, camera sensors in USB cameras or +connected to SoCs, which pass information about them to bridge drivers, usually +in their platform data. + +There are however also situations, where subdevices have to be registered +asynchronously to bridge devices. An example of such a configuration is Device +Tree based systems, on which information about subdevices is made available to +the system indpendently from the bridge devices, e.g. when subdevices are +defined in DT as I2C device nodes. The API, used in this second case is +described further below. + +Using one or the other registration method only affects the probing process, the +run-time bridge-subdevice interaction is in both cases the same. + +In the synchronous case a device (bridge) driver needs to register the +v4l2_subdev with the v4l2_device: int err = v4l2_device_register_subdev(v4l2_dev, sd); @@ -394,6 +413,25 @@ controlled through GPIO pins. This distinction is only relevant when setting up the device, but once the subdev is registered it is completely transparent. +In the asynchronous case subdevices register themselves using the +v4l2_async_register_subdev() function. Unregistration is performed, using the +v4l2_async_unregister_subdev() call. Subdevices registered this way are stored +on a global list of subdevices, ready to be picked up by bridge drivers. + +Bridge drivers in turn have to register a notifier object with an array of +subdevice descriptors, that the bridge device needs for its operation. This is +performed using the v4l2_async_notifier_register() call. To unregister the +notifier the driver has to call v4l2_async_notifier_unregister(). The former of +the two functions takes two arguments: a pointer to struct v4l2_device and a +pointer to struct v4l2_async_notifier. The latter contains a pointer to an array +of pointers to subdevice descriptors of type struct v4l2_async_subdev type. The +V4L2 core will then use these descriptors to match asynchronously registered +subdevices to them. If a match is detected the .bound() notifier callback is +called. After all subdevices have been located the .complete() callback is +called. When a subdevice is removed from the system the .unbind() method is +called. All three callbacks are optional. + + V4L2 sub-device userspace API ----------------------------- @@ -1061,3 +1099,23 @@ available event type is 'class base + 1'. An example on how the V4L2 events may be used can be found in the OMAP 3 ISP driver (drivers/media/platform/omap3isp). + + +V4L2 clocks +----------- + +Many subdevices, like camera sensors, TV decoders and encoders, need a clock +signal to be supplied by the system. Often this clock is supplied by the +respective bridge device. The Linux kernel provides a Common Clock Framework for +this purpose, however, it is not (yet) available on all architectures. Besides, +the nature of the multi-functional (clock, data + synchronisation, I2C control) +connection of subdevices to the system might impose special requirements on the +clock API usage. For these reasons a V4L2 clock helper API has been developed +and is provided to bridge and subdevice drivers. + +The API consists of two parts: two functions to register and unregister a V4L2 +clock source: v4l2_clk_register() and v4l2_clk_unregister() and calls to control +a clock object, similar to respective generic clock API calls: v4l2_clk_get(), +v4l2_clk_put(), v4l2_clk_enable(), v4l2_clk_disable(), v4l2_clk_get_rate(), and +v4l2_clk_set_rate(). Clock suppliers have to provide clock operations, that will +be called when clock users invoke respective API methods.