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=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 D30BFC4743C for ; Wed, 23 Jun 2021 15:10:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B4E8A601FF for ; Wed, 23 Jun 2021 15:10:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230392AbhFWPM4 (ORCPT ); Wed, 23 Jun 2021 11:12:56 -0400 Received: from mslow1.mail.gandi.net ([217.70.178.240]:59177 "EHLO mslow1.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229523AbhFWPM4 (ORCPT ); Wed, 23 Jun 2021 11:12:56 -0400 Received: from relay9-d.mail.gandi.net (unknown [217.70.183.199]) by mslow1.mail.gandi.net (Postfix) with ESMTP id 5B18FD27FB for ; Wed, 23 Jun 2021 15:10:37 +0000 (UTC) Received: (Authenticated sender: jacopo@jmondi.org) by relay9-d.mail.gandi.net (Postfix) with ESMTPSA id C3868FF814; Wed, 23 Jun 2021 15:10:12 +0000 (UTC) Date: Wed, 23 Jun 2021 17:11:01 +0200 From: Jacopo Mondi To: Sakari Ailus Cc: linux-media@vger.kernel.org, Niklas =?utf-8?Q?S=C3=B6derlund?= , Kieran Bingham , Andrey Konovalov Subject: Re: [PATCH 1/6] Documentation: media: Improve camera sensor documentation Message-ID: <20210623151101.flfbfw2crpwqkpna@uno.localdomain> References: <20210622112200.13914-1-sakari.ailus@linux.intel.com> <20210622112200.13914-2-sakari.ailus@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20210622112200.13914-2-sakari.ailus@linux.intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org Hi Sakari, thanks for addressing comments on v1 just a few minros, the rest looks very good! On Tue, Jun 22, 2021 at 02:21:55PM +0300, Sakari Ailus wrote: > Modernise the documentation to make it more precise and update the use of > pixel rate control and various other changes. In particular: > > - Use non-proportional font for file names, properties as well as > controls. > > - The unit of the HBLANK control is pixels, not lines. > > - The unit of PIXEL_RATE control is pixels per second, not Hz. > > - Merge common requirements for CSI-2 and parallel busses. > > - Include all DT properties needed for assigned clocks. > > - Fix referencing the link rate control. > > - SMIA driver's new name is CCS driver. > > - The PIXEL_RATE control denotes pixel rate on the pixel array on camera > sensors. Do not suggest it is used to tell the maximum pixel rate on the > bus anymore. > > - Improve ReST syntax (plain struct and function names). > > - Remove the suggestion to use s_power() in receiver drivers. > > - Make MIPI website URL use HTTPS, add Wikipedia links to BT.601 and > BT.656. > > Fixes: e4cf8c58af75 ("media: Documentation: media: Document how to write camera sensor drivers") > Signed-off-by: Sakari Ailus > --- > .../driver-api/media/camera-sensor.rst | 45 +++---- > Documentation/driver-api/media/index.rst | 2 +- > .../driver-api/media/{csi2.rst => tx-rx.rst} | 114 +++++++++++------- > .../media/v4l/ext-ctrls-image-process.rst | 2 + > 4 files changed, 90 insertions(+), 73 deletions(-) > rename Documentation/driver-api/media/{csi2.rst => tx-rx.rst} (39%) > > diff --git a/Documentation/driver-api/media/camera-sensor.rst b/Documentation/driver-api/media/camera-sensor.rst > index 7160336aa475..c7d4891bd24e 100644 > --- a/Documentation/driver-api/media/camera-sensor.rst > +++ b/Documentation/driver-api/media/camera-sensor.rst > @@ -3,10 +3,10 @@ > Writing camera sensor drivers > ============================= > > -CSI-2 > ------ > +CSI-2 and parallel (BT.601 and BT.656) busses > +--------------------------------------------- > > -Please see what is written on :ref:`MIPI_CSI_2`. > +Please see :ref:`transmitter-receiver`. > > Handling clocks > --------------- > @@ -26,15 +26,16 @@ user. > ACPI > ~~~~ > > -Read the "clock-frequency" _DSD property to denote the frequency. The driver can > -rely on this frequency being used. > +Read the ``clock-frequency`` _DSD property to denote the frequency. The driver > +can rely on this frequency being used. > > Devicetree > ~~~~~~~~~~ > > -The currently preferred way to achieve this is using "assigned-clock-rates" > -property. See Documentation/devicetree/bindings/clock/clock-bindings.txt for > -more information. The driver then gets the frequency using clk_get_rate(). > +The currently preferred way to achieve this is using ``assigned-clocks``, > +``assigned-clock-parents`` and ``assigned-clock-rates`` properties. See > +``Documentation/devicetree/bindings/clock/clock-bindings.txt`` for more > +information. The driver then gets the frequency using ``clk_get_rate()``. > > This approach has the drawback that there's no guarantee that the frequency > hasn't been modified directly or indirectly by another driver, or supported by > @@ -55,7 +56,7 @@ processing pipeline as one or more sub-devices with different cropping and > scaling configurations. The output size of the device is the result of a series > of cropping and scaling operations from the device's pixel array's size. > > -An example of such a driver is the smiapp driver (see drivers/media/i2c/smiapp). > +An example of such a driver is the CCS driver (see ``drivers/media/i2c/ccs``). > > Register list based drivers > ~~~~~~~~~~~~~~~~~~~~~~~~~~~ > @@ -67,7 +68,7 @@ level are independent. How a driver picks such configuration is based on the > format set on a source pad at the end of the device's internal pipeline. > > Most sensor drivers are implemented this way, see e.g. > -drivers/media/i2c/imx319.c for an example. > +``drivers/media/i2c/imx319.c`` for an example. > > Frame interval configuration > ---------------------------- > @@ -94,9 +95,10 @@ large variety of devices beyond camera sensors. Devices that have no analogue > crop, use the full source image size, i.e. pixel array size. > > Horizontal and vertical blanking are specified by ``V4L2_CID_HBLANK`` and > -``V4L2_CID_VBLANK``, respectively. The unit of these controls are lines. The > -pixel rate is specified by ``V4L2_CID_PIXEL_RATE`` in the same sub-device. The > -unit of that control is Hz. > +``V4L2_CID_VBLANK``, respectively. The unit of the ``V4L2_CID_HBLANK`` control > +is pixels and the unit of the ``V4L2_CID_VBLANK`` is lines. The pixel rate in > +the sensor's **pixel array** is specified by ``V4L2_CID_PIXEL_RATE`` in the same > +sub-device. The unit of that control is pixels per second. > > Register list based drivers need to implement read-only sub-device nodes for the > purpose. Devices that are not register list based need these to configure the > @@ -125,14 +127,14 @@ general, the device must be powered on at least when its registers are being > accessed and when it is streaming. > > Existing camera sensor drivers may rely on the old > -:c:type:`v4l2_subdev_core_ops`->s_power() callback for bridge or ISP drivers to > +struct v4l2_subdev_core_ops->s_power() callback for bridge or ISP drivers to > manage their power state. This is however **deprecated**. If you feel you need > to begin calling an s_power from an ISP or a bridge driver, instead please add > runtime PM support to the sensor driver you are using. Likewise, new drivers > should not use s_power. > > Please see examples in e.g. ``drivers/media/i2c/ov8856.c`` and > -``drivers/media/i2c/smiapp/smiapp-core.c``. The two drivers work in both ACPI > +``drivers/media/i2c/ccs/ccs-core.c``. The two drivers work in both ACPI > and DT based systems. > > Control framework > @@ -149,16 +151,3 @@ used to obtain device's power state after the power state transition: > The function returns a non-zero value if it succeeded getting the power count or > runtime PM was disabled, in either of which cases the driver may proceed to > access the device. > - > -Controls > --------- > - > -For camera sensors that are connected to a bus where transmitter and receiver > -require common configuration set by drivers, such as CSI-2 or parallel (BT.601 > -or BT.656) bus, the ``V4L2_CID_LINK_FREQ`` control is mandatory on transmitter > -drivers. Receiver drivers can use the ``V4L2_CID_LINK_FREQ`` to query the > -frequency used on the bus. > - > -The transmitter drivers should also implement ``V4L2_CID_PIXEL_RATE`` control in > -order to tell the maximum pixel rate to the receiver. This is required on raw > -camera sensors. > diff --git a/Documentation/driver-api/media/index.rst b/Documentation/driver-api/media/index.rst > index 813d7db59da7..08e206567408 100644 > --- a/Documentation/driver-api/media/index.rst > +++ b/Documentation/driver-api/media/index.rst > @@ -37,7 +37,7 @@ Documentation/userspace-api/media/index.rst > rc-core > mc-core > cec-core > - csi2 > + tx-rx > camera-sensor > > drivers/index > diff --git a/Documentation/driver-api/media/csi2.rst b/Documentation/driver-api/media/tx-rx.rst > similarity index 39% > rename from Documentation/driver-api/media/csi2.rst > rename to Documentation/driver-api/media/tx-rx.rst > index 11c52b0be8b8..6331f93fb249 100644 > --- a/Documentation/driver-api/media/csi2.rst > +++ b/Documentation/driver-api/media/tx-rx.rst > @@ -1,39 +1,71 @@ > .. SPDX-License-Identifier: GPL-2.0 > > -.. _MIPI_CSI_2: > +.. _transmitter-receiver: > + > +Pixel data transmitter and receiver drivers > +=========================================== > + > +V4L2 supports various devices that transmit and receiver pixel data. Examples of s/and receiver/and receives/ > +these devices include a camera sensor, a TV tuner and a parallel or a CSI-2 > +receiver in an SoC. > + > +Bus types > +--------- > + > +The following busses are the most common. This section discusses these two only. > > MIPI CSI-2 > -========== > +^^^^^^^^^^ > > CSI-2 is a data bus intended for transferring images from cameras to > the host SoC. It is defined by the `MIPI alliance`_. > > -.. _`MIPI alliance`: http://www.mipi.org/ > +.. _`MIPI alliance`: https://www.mipi.org/ > > -Media bus formats > ------------------ > +Parallel > +^^^^^^^^ > > -See :ref:`v4l2-mbus-pixelcode` for details on which media bus formats should > -be used for CSI-2 interfaces. > +`BT.601`_ and `BT.656`_ are the most common parallel busses. > + > +.. _`BT.601`: https://en.wikipedia.org/wiki/Rec._601 > +.. _`BT.656`: https://en.wikipedia.org/wiki/ITU-R_BT.656 > > Transmitter drivers > ------------------- > > -CSI-2 transmitter, such as a sensor or a TV tuner, drivers need to > -provide the CSI-2 receiver with information on the CSI-2 bus > -configuration. These include the V4L2_CID_LINK_FREQ and > -V4L2_CID_PIXEL_RATE controls and > -(:c:type:`v4l2_subdev_video_ops`->s_stream() callback). These > -interface elements must be present on the sub-device represents the > -CSI-2 transmitter. > +Transmitter drivers generally need to provide the receiver drivers with the > +configuration of the transmitter. What is required depends on the type of the > +bus. These are common for both busses. > + > +Media bus pixel code > +^^^^^^^^^^^^^^^^^^^^ > + > +The media bus pixel codes document parallel formats. Should the pixel data be > +transported over a serial bus, the media bus pixel code that describes a > +parallel format that transfers a sample on a single clock cycle is used. I guess you intend to document that, in example, MEDIA_BUS_FMT_YUYV8_2X8 has to be used on parallel busses, as the bus width is meaningful, while MEDIA_BUS_FMT_YUYV8_1X16 should be used on serial busses as the bus width it's not. I guess this could be reported as an example ? > + > +See :ref:`v4l2-mbus-pixelcode`. > + > +Link frequency > +^^^^^^^^^^^^^^ > + > +The :ref:`V4L2_CID_LINK_FREQ ` control is used to tell the > +receiver the frequency of the bus (i.e. it is not the same as the symbol rate). > + > +``.s_stream()`` callback > +^^^^^^^^^^^^^^^^^^^^^^^^ > > -The V4L2_CID_LINK_FREQ control is used to tell the receiver driver the > -frequency (and not the symbol rate) of the link. The V4L2_CID_PIXEL_RATE > -control may be used by the receiver to obtain the pixel rate the transmitter > -uses. The :c:type:`v4l2_subdev_video_ops`->s_stream() callback provides an > -ability to start and stop the stream. > +The struct struct v4l2_subdev_video_ops->s_stream() callback is used by the > +receiver driver to control the transmitter driver's streaming state. > > -The value of the V4L2_CID_PIXEL_RATE is calculated as follows:: > + > +CSI-2 transmitter drivers > +------------------------- > + > +Pixel rate > +^^^^^^^^^^ > + > +The pixel rate on the bus is calculated as follows:: > > pixel_rate = link_freq * 2 * nr_of_lanes * 16 / k / bits_per_sample > > @@ -45,27 +77,38 @@ where > * - variable or constant > - description > * - link_freq > - - The value of the V4L2_CID_LINK_FREQ integer64 menu item. > + - The value of the ``V4L2_CID_LINK_FREQ`` integer64 menu item. > * - nr_of_lanes > - Number of data lanes used on the CSI-2 link. This can > be obtained from the OF endpoint configuration. > * - 2 > - - Two bits are transferred per clock cycle per lane. > + - Data is transferred on both rising and falling edge of the signal. > * - bits_per_sample > - Number of bits per sample. > * - k > - 16 for D-PHY and 7 for C-PHY > > -The transmitter drivers must, if possible, configure the CSI-2 > -transmitter to *LP-11 mode* whenever the transmitter is powered on but > -not active, and maintain *LP-11 mode* until stream on. Only at stream > -on should the transmitter activate the clock on the clock lane and > -transition to *HS mode*. > +.. note:: > + > + The pixel rate calculated this way is **not** be the same thing than > + the pixel rate on the camera sensor's pixel array. .. as reported by the V4L2_CID_PIXEL_RATE control. > + > +LP-11 and LP-111 modes > +^^^^^^^^^^^^^^^^^^^^^^ > + > +The transmitter drivers must, if possible, configure the CSI-2 transmitter to s/drivers/driver/ Or if you want to keep it plural drop "The" ? > +*LP-11 or LP-111 mode* whenever the transmitter is powered on but not active, > +and maintain *LP-11 or LP-111 mode* until stream on. Only at stream on should > +the transmitter activate the clock on the clock lane and transition to *HS "Only at stream on time the transmitter should" Sounds better to me, but not being a native speaker I might very well be wrong :) All minors, thanks for clearing this up Reviewed-by: Jacopo Mondi Thanks j > +mode*. > > Some transmitters do this automatically but some have to be explicitly > programmed to do so, and some are unable to do so altogether due to > hardware constraints. > > +The receiver thus need to be configured to expect LP-11 or LP-111 mode from the > +transmitter before the transmitter driver's ``.s_stream()`` op is called. > + > Stopping the transmitter > ^^^^^^^^^^^^^^^^^^^^^^^^ > > @@ -75,20 +118,3 @@ stream at a frame boundary whereas others stop immediately, > effectively leaving the current frame unfinished. The receiver driver > should not make assumptions either way, but function properly in both > cases. > - > -Receiver drivers > ----------------- > - > -Before the receiver driver may enable the CSI-2 transmitter by using > -the :c:type:`v4l2_subdev_video_ops`->s_stream(), it must have powered > -the transmitter up by using the > -:c:type:`v4l2_subdev_core_ops`->s_power() callback. This may take > -place either indirectly by using :c:func:`v4l2_pipeline_pm_get` or > -directly. > - > -Formats > -------- > - > -The media bus pixel codes document parallel formats. Should the pixel data be > -transported over a serial bus, the media bus pixel code that describes a > -parallel format that transfers a sample on a single clock cycle is used. > diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-image-process.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-image-process.rst > index 87698c15c027..37dad2f4df8c 100644 > --- a/Documentation/userspace-api/media/v4l/ext-ctrls-image-process.rst > +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-image-process.rst > @@ -20,6 +20,8 @@ Image Process Control IDs > ``V4L2_CID_IMAGE_PROC_CLASS (class)`` > The IMAGE_PROC class descriptor. > > +.. _v4l2-cid-link-freq: > + > ``V4L2_CID_LINK_FREQ (integer menu)`` > Data bus frequency. Together with the media bus pixel code, bus type > (clock cycles per sample), the data bus frequency defines the pixel > -- > 2.30.2 >