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 52121C433F5 for ; Wed, 6 Apr 2022 16:41:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237952AbiDFQn1 (ORCPT ); Wed, 6 Apr 2022 12:43:27 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40816 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237956AbiDFQm0 (ORCPT ); Wed, 6 Apr 2022 12:42:26 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0CB70ECDB4 for ; Wed, 6 Apr 2022 07:01:35 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id A026FB80EEB for ; Wed, 6 Apr 2022 14:01:34 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 89B0BC385A3; Wed, 6 Apr 2022 14:01:31 +0000 (UTC) Message-ID: <275d0222-b690-0d99-4ef5-72ecb070a2cd@xs4all.nl> Date: Wed, 6 Apr 2022 16:01:29 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.6.1 Subject: Re: [PATCH v6 8/8] media: Documentation: add documentation about subdev state Content-Language: en-US To: Tomi Valkeinen , linux-media@vger.kernel.org, sakari.ailus@linux.intel.com, Jacopo Mondi , Laurent Pinchart , niklas.soderlund+renesas@ragnatech.se, Mauro Carvalho Chehab , Pratyush Yadav References: <20220324080030.216716-1-tomi.valkeinen@ideasonboard.com> <20220324080030.216716-9-tomi.valkeinen@ideasonboard.com> From: Hans Verkuil In-Reply-To: <20220324080030.216716-9-tomi.valkeinen@ideasonboard.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org On 24/03/2022 09:00, Tomi Valkeinen wrote: > Add documentation about centrally managed subdev state. > > Signed-off-by: Tomi Valkeinen > Reviewed-by: Jacopo Mondi > Reviewed-by: Hans Verkuil > Reviewed-by: Laurent Pinchart > --- > .../driver-api/media/v4l2-subdev.rst | 75 +++++++++++++++++++ > 1 file changed, 75 insertions(+) > > diff --git a/Documentation/driver-api/media/v4l2-subdev.rst b/Documentation/driver-api/media/v4l2-subdev.rst > index 08ea2673b19e..7fa950b1bff0 100644 > --- a/Documentation/driver-api/media/v4l2-subdev.rst > +++ b/Documentation/driver-api/media/v4l2-subdev.rst > @@ -518,6 +518,81 @@ 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 > +device configuration. This is often implemented as e.g. an array of struct > +v4l2_mbus_framefmt, one entry for each pad, and similarly for crop and compose > +rectangles. > + > +In addition to the active configuration, each subdev file handle has an array of > +struct v4l2_subdev_pad_config, managed by the V4L2 core, which contains the try > +configuration. > + > +To simplify the subdev drivers the V4L2 subdev API now optionally supports a > +centrally managed active configuration represented by > +:c:type:`v4l2_subdev_state`. One instance of state, which contains the active > +device configuration, is stored in the sub-device itself as part of > +the :c:type:`v4l2_subdev` structure, while the core associates a try state to > +each open file handle, to store the try configuration related to that file > +handle. > + > +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() > +before registering the sub-device. They must also call v4l2_subdev_cleanup() > +to release all the allocated resources before unregistering the sub-device. > +The core automatically allocates and initializes a state for each open file > +handle to store the try configurations and frees it when closing the file > +handle. > + > +V4L2 sub-device operations that use both the :ref:`ACTIVE and TRY formats > +` receive the correct state to operate on through > +the 'state' parameter. The state must be locked and unlocked by the > +caller by calling :c:func:`v4l2_subdev_lock_state()` and > +:c:func:`v4l2_subdev_unlock_state()`. The caller can do so by calling the subdev > +operation through the :c:func:`v4l2_subdev_call_state_active()` macro. > + > +Operations that do not receive a state parameter implicitly operate on the > +subdevice active state, which drivers can exclusively access by > +calling :c:func:`v4l2_subdev_lock_and_get_active_state()`. The sub-device active > +state must equally be released by calling :c:func:`v4l2_subdev_unlock_state()`. > + > +Drivers must never manually access the state stored in the :c:type:`v4l2_subdev` > +or in the file handle without going through the designated helpers. > + > +While the V4L2 core passes the correct try or active state to the > +subdevice operations, some existing device drivers pass a NULL state > +when calling operations with :c:func:`v4l2_subdev_call()`. This legacy > +construct causes issues with subdevice drivers that let the V4L2 core > +manage the active state, as they expect to receive the appropriate state > +as a parameter. To help the conversion of subdevice drivers to a managed > +active state without having to convert all callers at the same time, the > +:c:func:`v4l2_subdev_lock_and_return_state()` helper function can be This is an old name, right? It's no longer called v4l2_subdev_lock_and_return_state. Note that the commit log of patch 4 also refers to this old name. Actually, isn't this now replaced by the subdev op wrappers? (I might be wrong, I don't have much time to review this patch). > +used by subdevice drivers to retrieve the active state if a NULL state > +is passed to the subdevice operation. > + > +:c:func:`v4l2_subdev_lock_and_return_state()` should only be used when porting > +an existing driver to the new state management when it cannot be guaranteed > +that the current callers will pass the state properly. The function prints a > +notice when the passed state is NULL to encourage the porting of the callers > +to the new state management. > + > +The whole subdev state is in reality split into three parts: the > +v4l2_subdev_state, subdev controls and subdev driver's internal state. In the > +future these parts should be combined into a single state. For the time being > +we need a way to handle the locking for these parts. This can be accomplished > +by sharing a lock. The v4l2_ctrl_handler already supports this via its 'lock' > +pointer and the same model is used with states. The driver can do the following > +before calling v4l2_subdev_init_finalize(): > + > +.. code-block:: c > + > + sd->ctrl_handler->lock = &priv->mutex; > + sd->state_lock = &priv->mutex; > + > +This shares the driver's private mutex between the controls and the states. > + > V4L2 sub-device functions and data structures > --------------------------------------------- > Regards, Hans