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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2D767C433FE for ; Fri, 17 Dec 2021 09:22:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234092AbhLQJWy (ORCPT ); Fri, 17 Dec 2021 04:22:54 -0500 Received: from perceval.ideasonboard.com ([213.167.242.64]:51228 "EHLO perceval.ideasonboard.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234088AbhLQJWy (ORCPT ); Fri, 17 Dec 2021 04:22:54 -0500 Received: from [192.168.1.111] (91-156-85-209.elisa-laajakaista.fi [91.156.85.209]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 5275692A; Fri, 17 Dec 2021 10:22:52 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1639732972; bh=CyesS9PHneRUxLDuJtZxi6ADFy1d9bRBBjlqCuE1K5A=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=Yk+jDLagzvWP8gCD6Fk3sVQo747tUkID2D/HAILgs865NwhKCvTE3IggYCxM9zO3k txUYla5LHIv+zwdItbd8hI4044lfICachkcPvKEhiZxhyUHt38t7Vyti71ozbuLrDr aJ1N2a14/ikp+y1MSaBMZsCrqGEz4qR7eVB2obg4= Subject: Re: [PATCH v10 06/38] media: Documentation: add documentation about subdev state To: Jacopo Mondi Cc: linux-media@vger.kernel.org, sakari.ailus@linux.intel.com, Jacopo Mondi , Laurent Pinchart , niklas.soderlund+renesas@ragnatech.se, Mauro Carvalho Chehab , Hans Verkuil , Pratyush Yadav References: <20211130141536.891878-1-tomi.valkeinen@ideasonboard.com> <20211130141536.891878-7-tomi.valkeinen@ideasonboard.com> <20211214083151.ipksg4fwxuu6u2ow@uno.localdomain> From: Tomi Valkeinen Message-ID: Date: Fri, 17 Dec 2021 11:22:48 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.14.0 MIME-Version: 1.0 In-Reply-To: <20211214083151.ipksg4fwxuu6u2ow@uno.localdomain> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org On 14/12/2021 10:31, Jacopo Mondi wrote: > Hi Tomi, > > On Tue, Nov 30, 2021 at 04:15:04PM +0200, Tomi Valkeinen wrote: >> Add documentation about centrally managed subdev state. >> >> Signed-off-by: Tomi Valkeinen >> --- >> .../driver-api/media/v4l2-subdev.rst | 28 +++++++++++++++++++ >> 1 file changed, 28 insertions(+) >> >> diff --git a/Documentation/driver-api/media/v4l2-subdev.rst b/Documentation/driver-api/media/v4l2-subdev.rst >> index 7736da077fb8..db012729f8e3 100644 >> --- a/Documentation/driver-api/media/v4l2-subdev.rst >> +++ b/Documentation/driver-api/media/v4l2-subdev.rst >> @@ -518,6 +518,34 @@ The :c:func:`v4l2_i2c_new_subdev` function will call >> :c:type:`i2c_board_info` structure using the ``client_type`` and the >> ``addr`` to fill it. >> >> +Centrally managed subdev active state >> +------------------------------------- >> + >> +Traditionally V4L2 subdev drivers maintained internal state for the active >> +configuration for the subdev. This is often implemented as an array of struct >> +v4l2_mbus_framefmt, one entry for each pad. > > Not only v4l2_mbus_framefmt, but the 'active' configuration also > contains cropping rectangles. I would drop the last statement maybe ? > >> + >> +In addition to the active configuration, each subdev filehandle has an array of >> +struct v4l2_subdev_pad_config, managed by V4L2 core, which contains the TRY >> +configuration. >> + >> +To simplify the subdev drivers the V4L2 subdev API now optionally supports a >> +centrally managed active configuration. A subdev driver must use > > I would here explain what active and try states are and where they > live. > > "a centrally managed active configuration represented by > :c:type:`v4l2_subdev_state`. One instance of state, which contains > the active device configuration, is associated with the sub-device itself as > part of the :c:type:`v4l2_subdev` structure, while the core associates to > each open file handle a try state, which contains the configuration > valid in the file-handle context only." > >> +v4l2_subdev_init_finalize() to initialize the active state between calls to >> +media_entity_pads_init() and v4l2_*_register_subdev(), and must call >> +v4l2_subdev_cleanup() to free the state. > > "Sub-device drivers can opt-in and use state to manage their active > configuration by initializing the subdevice state with a call to > v4l2_subdev_init_finalize() as the last operation before registering > the sub-device. They must also call v4l2_subdev_cleanup() to release > all the acquired resources before unregistering the sub-device. The > core automatically initializes a state for each open file handle where > to store the try configurations and releases them at file handle > closing time." > >> + >> +The active state must be locked before access, and that can be done with >> +v4l2_subdev_lock_state() or v4l2_subdev_lock_active_state(). > > I would also explain which state to use and when. > > "V4L2 sub-device operations that operates on both the :ref:`ACTIVE and > TRY formats ` receive by the core the > correct state to operate on an operation parameter. The sub-device driver > can access and modify the configuration stored in the provided state > after having exclusively acquired it by calling > :c:func:`v4l2_subdev_lock_state()` and released it with > :c:func:`v4l2_subdev_unlock_state()` when done. > > Operations that do not receive a state parameter implicitly operates > on the subdevice active state, which drivers can exclusively access by > calling :c:func:`v4l2_subdev_lock_active_state()`. The sub-device active > state should equally be released by calling > :c:func:`v4l2_subdev_unlock_state()`. > > In no occasions driver should try to manually access the state stored > in the :c:type`v4l2_subdev` or in the file handle without going > through the designated helpers". > >> + >> +The V4L2 core will pass either the TRY or ACTIVE state to various subdev ops. >> +Unfortunately not all the subdev drivers comply with this yet, and may pass > > If I'm not mistaken it's not the subdev drivers but the top drivers > which might not comply. No, it's for any callers of subdev ops (core, top-drivers, subdev drivers). I'll change it to "not all callers comply". Thanks Jacopo and Laurent. I like this method of writing docs! Tomi