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 32769C433EF for ; Thu, 16 Dec 2021 14:50:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234962AbhLPOuI (ORCPT ); Thu, 16 Dec 2021 09:50:08 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48372 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230071AbhLPOuI (ORCPT ); Thu, 16 Dec 2021 09:50:08 -0500 Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [IPv6:2001:4b98:dc2:55:216:3eff:fef7:d647]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BA997C061574 for ; Thu, 16 Dec 2021 06:50:07 -0800 (PST) Received: from pendragon.ideasonboard.com (62-78-145-57.bb.dnainternet.fi [62.78.145.57]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id B06773F6; Thu, 16 Dec 2021 15:50:04 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1639666204; bh=VPViw9qOTEE3KHCAytU7mcJVcdHGY4HZ+0aYgb+K5wM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=GROrdfhIbrGBSCn/iVwN+qounV3s4e7uOwQPATtzKJdEH613mLpU74yHOswjhThNR oSzAIumYq8kj9hMSTI4UQH4TbWy6/jj0AmCLy4P2jeF86I+1YVnuAuuqzUimzBSG0Z qF4/oEWvxSEmxjZXbq9pKtZVRKTlQ1038FpO6c5Y= Date: Thu, 16 Dec 2021 16:50:02 +0200 From: Laurent Pinchart To: Jacopo Mondi Cc: Tomi Valkeinen , linux-media@vger.kernel.org, sakari.ailus@linux.intel.com, Jacopo Mondi , niklas.soderlund+renesas@ragnatech.se, Mauro Carvalho Chehab , Hans Verkuil , Pratyush Yadav Subject: Re: [PATCH v10 06/38] media: Documentation: add documentation about subdev state Message-ID: References: <20211130141536.891878-1-tomi.valkeinen@ideasonboard.com> <20211130141536.891878-7-tomi.valkeinen@ideasonboard.com> <20211214083151.ipksg4fwxuu6u2ow@uno.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20211214083151.ipksg4fwxuu6u2ow@uno.localdomain> Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org Hello, On Tue, Dec 14, 2021 at 09:31:51AM +0100, Jacopo Mondi wrote: > 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 s/operates/operate/ > TRY formats ` receive by the core the s/by the/from the/ (or just s/by the core //) > 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 s/exclusively acquired/locked/ > :c:func:`v4l2_subdev_lock_state()` and released it with > :c:func:`v4l2_subdev_unlock_state()` when done. "The driver must then call :c:func:`v4l2_subdev_unlock_state()` to unlock the 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. > > > +NULL for the ACTIVE case. This is only a problem for subdev drivers which use > > +the centrally managed active state and are used in media pipelines with older > > +subdev drivers. In these cases the called subdev ops must also handle the NULL > > +case. This can be easily managed by the use of > > +v4l2_subdev_validate_and_lock_state() helper. > > depending on the previous suggestion to fail hard if !state, this > might be removed ? Or expanded with a note that this option is only possible when transitioning existing subdev drivers, and that the function will eventually be removed. And maybe that it prints a warning, and that host drivers must be converted as a result. Otherwise this looks good to me. On a side note, I think we should prepare to allow subdev drivers to subclass the state structure at some point :-) > > + > > V4L2 sub-device functions and data structures > > --------------------------------------------- > > -- Regards, Laurent Pinchart