Re: [PATCH v2 4/5] media: Documentation: Add Mali-C55 ISP Documentation

Kieran Bingham
2024-02-25T21:23:19Z

Hi Dan,

Quoting Daniel Scally (2024-02-14 14:19:05)
> Add a documentation page for the mali-c55 driver, which gives a brief
> overview of the hardware and explains how to use the driver's capture
> devices and the crop/scaler functions.
>
> Acked-by: Nayden Kanchev <nayden.kanchev@arm.com>
> Signed-off-by: Daniel Scally <dan.scally@ideasonboard.com>
> ---
> Changes in v2:
>
> - none
>
> .../admin-guide/media/mali-c55-graph.dot | 19 ++
> Documentation/admin-guide/media/mali-c55.rst | 318 ++++++++++++++++++
> .../admin-guide/media/v4l-drivers.rst | 1 +
> 3 files changed, 338 insertions(+)
> create mode 100644 Documentation/admin-guide/media/mali-c55-graph.dot
> create mode 100644 Documentation/admin-guide/media/mali-c55.rst
>
> diff --git a/Documentation/admin-guide/media/mali-c55-graph.dot b/Documentation/admin-guide/media/mali-c55-graph.dot
> new file mode 100644
> index 000000000000..0775ba42bf4c
> --- /dev/null
> +++ b/Documentation/admin-guide/media/mali-c55-graph.dot
> @@ -0,0 +1,19 @@
> +digraph board {
> + rankdir=TB
> + n00000001 [label="{{} | mali-c55 tpg\n/dev/v4l-subdev0 | {<port0> 0}}", shape=Mrecord, style=filled, fillcolor=green]
> + n00000001:port0 -> n00000003:port0 [style=dashed]
> + n00000003 [label="{{<port0> 0} | mali-c55 isp\n/dev/v4l-subdev1 | {<port1> 1 | <port2> 2}}", shape=Mrecord, style=filled, fillcolor=green]
> + n00000003:port1 -> n00000007:port0 [style=bold]
> + n00000003:port2 -> n00000007:port2 [style=bold]
> + n00000003:port1 -> n0000000b:port0 [style=bold]
> + n00000007 [label="{{<port0> 0 | <port2> 2} | mali-c55 resizer fr\n/dev/v4l-subdev2 | {<port1> 1}}", shape=Mrecord, style=filled, fillcolor=green]
> + n00000007:port1 -> n0000000e [style=bold]
> + n0000000b [label="{{<port0> 0} | mali-c55 resizer ds\n/dev/v4l-subdev3 | {<port1> 1}}", shape=Mrecord, style=filled, fillcolor=green]
> + n0000000b:port1 -> n00000012 [style=bold]
> + n0000000e [label="mali-c55 fr\n/dev/video0", shape=box, style=filled, fillcolor=yellow]
> + n00000012 [label="mali-c55 ds\n/dev/video1", shape=box, style=filled, fillcolor=yellow]
> + n00000022 [label="{{<port0> 0} | csi2-rx\n/dev/v4l-subdev4 | {<port1> 1}}", shape=Mrecord, style=filled, fillcolor=green]
> + n00000022:port1 -> n00000003:port0
> + n00000027 [label="{{} | imx415 1-001a\n/dev/v4l-subdev5 | {<port0> 0}}", shape=Mrecord, style=filled, fillcolor=green]
> + n00000027:port0 -> n00000022:port0 [style=bold]
> +}
> \ No newline at end of file
> diff --git a/Documentation/admin-guide/media/mali-c55.rst b/Documentation/admin-guide/media/mali-c55.rst
> new file mode 100644
> index 000000000000..83f630c3bd9d
> --- /dev/null
> +++ b/Documentation/admin-guide/media/mali-c55.rst
> @@ -0,0 +1,318 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +==========================================
> +ARM Mali-C55 Image Signal Processor driver
> +==========================================
> +
> +Introduction
> +============
> +
> +This file documents the driver for ARM's Mali-C55 Image Signal Processor. The
> +driver is located under drivers/media/platform/arm/mali-c55.
> +
> +The Mali-C55 ISP receives data in either raw Bayer format or RGB/YUV format from
> +sensors through either a parallel interface or a memory bus before processing it
> +and outputting it through an internal DMA engine. Two output pipelines are
> +possible (though one may not be fitted, depending on the implementation). These
> +are referred to as "Full resolution" and "Downscale", but the naming is historic
> +and both pipes are capable of cropping/scaling operations. An integrated test
> +pattern generator can be used to drive the ISP and produce image data in the
> +absence of a connected camera sensor. The driver module is named mali_c55, and
> +is enabled through the CONFIG_VIDEO_MALI_C55 config option.

Can it handle metadata or other datatypes separately? anything else
that's worthy of mention? Or maybe not yet in this version.

> +
> +The driver implements V4L2, Media Controller and V4L2 Subdevice interfaces and
> +expects camera sensors connected to the ISP to have V4L2 subdevice interfaces.
> +
> +Mali-C55 ISP hardware
> +=====================
> +
> +A high level functional view of the Mali-C55 ISP is presented below. The ISP
> +takes input from either a live source or through a DMA engine for memory input,
> +depending on the SoC integration.::
> +
> + +---------+ +----------+ +--------+
> + | Sensor |--->| CSI-2 Rx | "Full Resolution" | DMA |
> + +---------+ +----------+ |\ Output +--->| Writer |
> + | | \ | +--------+
> + | | \ +----------+ +------+---> Streaming I/O
> + +------------+ +------->| | | | |
> + | | | |-->| Mali-C55 |--+
> + | DMA Reader |--------------->| | | ISP | |
> + | | | / | | | +---> Streaming I/O
> + +------------+ | / +----------+ | |
> + |/ +------+
> + | +--------+
> + +--->| DMA |
> + "Downscaled" | Writer |
> + Output +--------+
> +
> +Media Controller Topology
> +=========================
> +
> +An example of the ISP's topology (as implemented in a system with an IMX415
> +camera sensor and generic CSI-2 receiver) is below:
> +
> +
> +.. kernel-figure:: mali-c55-graph.dot
> + :alt: mali-c55-graph.dot
> + :align: center
> +
> +The driver has 4 V4L2 subdevices:
> +
> +- `mali_c55 isp`: Responsible for configuring input crop and color space
> + conversion
> +- `mali_c55 tpg`: The test pattern generator, emulating a camera sensor.
> +- `mali_c55 resizer fr`: The Full-Resolution pipe resizer
> +- `mali_c55 resizer ds`: The Downscale pipe resizer
> +
> +The driver has 2 V4L2 video devices:
> +
> +- `mali-c55 fr`: The full-resolution pipe's capture device
> +- `mali-c55 ds`: The downscale pipe's capture device
> +
> +Idiosyncrasies
> +--------------
> +
> +**mali-c55 isp**
> +The `mali-c55 isp` subdevice has a single sink pad to which all sources of data
> +should be connected. The active source is selected by enabling the appropriate
> +media link and disabling all others.

By that I presume you mean you can only accept a single input link at a
time?

> The ISP has two source pads, reflecting the
> +different paths through which it can internally route data. Tap points within
> +the ISP allow users to divert data to avoid processing by some or all of the
> +hardware's processing steps. The diagram below is intended only to highlight how
> +the bypassing works and is not a true reflection of those processing steps; for
> +a high-level functional block diagram see ARM's developer page for the
> +ISP [3]_::
> +
> + +--------------------------------------------------------------+
> + | Possible Internal ISP Data Routes |
> + | +------------+ +----------+ +------------+ |
> + +---+ | | | | | Colour | +---+
> + | 0 |--+-->| Processing |->| Demosaic |->| Space |--->| 1 |
> + +---+ | | | | | | Conversion | +---+
> + | | +------------+ +----------+ +------------+ |
> + | | +---+
> + | +---------------------------------------------------| 2 |
> + | +---+
> + | |
> + +--------------------------------------------------------------+
> +
> +
> +.. flat-table::
> + :header-rows: 1
> +
> + * - Pad
> + - Direction
> + - Purpose
> +
> + * - 0
> + - sink
> + - Data input, connected to the TPG and camera sensors
> +
> + * - 1
> + - source
> + - RGB/YUV data, connected to the FR and DS V4L2 subdevices
> +
> + * - 2
> + - source
> + - RAW bayer data, connected to the FR V4L2 subdevices
> +
> +**mali-c55 resizer fr**
> +The `mali-c55 resizer fr` subdevice has two _sink_ pads to reflect the different
> +insertion points in the hardware (either RAW or demosaiced data):
> +
> +.. flat-table::
> + :header-rows: 1
> +
> + * - Pad
> + - Direction
> + - Purpose
> +
> + * - 0
> + - sink
> + - Data input connected to the ISP's demosaiced stream.
> +
> + * - 1
> + - source
> + - Data output connected to the capture video device
> +
> + * - 2
> + - sink
> + - Data input connected to the ISP's raw data stream
> +
> +The data source in use is selected through the routing API; two routes each of a
> +single stream are available:
> +
> +.. flat-table::
> + :header-rows: 1
> +
> + * - Sink Pad
> + - Source Pad
> + - Purpose
> +
> + * - 0
> + - 1
> + - Demosaiced data route
> +
> + * - 2
> + - 1
> + - Raw data route
> +
> +
> +If the demosaiced route is active then the FR pipe is only capable of output
> +in RGB/YUV formats. If the raw route is active then the output reflects the
> +input (which may be either Bayer or RGB/YUV data).
> +
> +Using the driver to capture video
> +=================================
> +
> +Using the media controller APIs we can configure the input source and ISP to
> +capture images in a variety of formats. In the examples below, configuring the
> +media graph is done with the v4l-utils [1]_ package's media-ctl utility.
> +Capturing the images is done with yavta [2]_.
> +
> +Configuring the input source
> +----------------------------
> +
> +The first step is to set the input source that we wish by enabling the correct
> +media link. Using the example topology above, we can select the TPG as follows:
> +
> +.. code-block:: none
> +
> + media-ctl -l "'lte-csi2-rx':1->'mali-c55 isp':0[0]"
> + media-ctl -l "'mali-c55 tpg':0->'mali-c55 isp':0[1]"
> +
> +Capturing bayer data from the source and processing to RGB/YUV
> +--------------------------------------------------------------
> +To capture 1920x1080 bayer data from the source and push it through the ISP's
> +full processing pipeline, we configure the data formats appropriately on the
> +source, ISP and resizer subdevices and set the FR resizer's routing to select
> +processed data. The media bus format on the resizer's source pad will be either
> +RGB121212_1X36 or YUV10_1X30, depending on whether you want to capture RGB or
> +YUV. The ISP's debayering block outputs RGB data natively, setting the source
> +pad format to YUV10_1X30 enables the colour space conversion block.
> +
> +In this example we target RGB565 output, so select RGB121212_1X36 as the resizer
> +source pad's format:
> +
> +.. code-block:: none
> +
> + # Set formats on the TPG and ISP
> + media-ctl -V "'mali-c55 tpg':0[fmt:SRGGB16_1X16/1920x1080]"
> + media-ctl -V "'mali-c55 isp':0[fmt:SRGGB16_1X16/1920x1080]"
> + media-ctl -V "'mali-c55 isp':1[fmt:SRGGB16_1X16/1920x1080]"
> +
> + # Set routing on the FR resizer
> + media-ctl -R "'mali-c55 resizer fr'[0/0->1/0[1],2/0->1/0[0]]"
> +
> + # Set format on the resizer, must be done AFTER the routing.
> + media-ctl -V "'mali-c55 resizer fr':1[fmt:RGB121212_1X36/1920x1080]"
> +
> +The downscale output can also be used to stream data at the same time. In this
> +case only processed data can be captured and so no routing need be set:

Is the route automatically reset? or is it just that the default route
is already the correct choice for this instance?

> +
> +.. code-block:: none
> +
> + # Set format on the resizer
> + media-ctl -V "'mali-c55 resizer ds':1[fmt:RGB121212_1X36/1920x1080]"
> +
> +Following which images can be captured from both the FR and DS output's video
> +devices (simultaneously, if desired):
> +
> +.. code-block:: none
> +
> + yavta -f RGB565 -s 1920x1080 -c10 /dev/video0
> + yavta -f RGB565 -s 1920x1080 -c10 /dev/video1
> +

Is there any synchronisation required? Can one pipe run without the
other if they are both enabled? or will stalling on one pipe stall the
other?

> +Cropping the image
> +~~~~~~~~~~~~~~~~~~
> +
> +Both the full resolution and downscale pipes can crop to a minimum resolution of
> +640x480. To crop the image simply configure the resizer's sink pad's crop and
> +compose rectangles and set the format on the video device:
> +
> +.. code-block:: none
> +
> + media-ctl -V "'mali-c55 resizer fr':0[fmt:RGB121212_1X36/1920x1080 crop:(480,270)/640x480 compose:(0,0)/640x480]"
> + media-ctl -V "'mali-c55 resizer fr':1[fmt:RGB121212_1X36/640x480]"
> + yavta -f RGB565 -s 640x480 -c10 /dev/video0
> +
> +Downscaling the image
> +~~~~~~~~~~~~~~~~~~~~~
> +
> +Both the full resolution and downscale pipes can downscale the image by up to 8x
> +provided the minimum 640x480 resolution is adhered to. For the best image result

'minimum 640x480 output resolution' I presume.

Maybe the ISP limits/restrictions need to be defined before here?

> +the scaling ratio for each dimension should be the same. To configure scaling we
> +use the compose rectangle on the resizer's sink pad:
> +
> +.. code-block:: none
> +
> + media-ctl -V "'mali-c55 resizer fr':0[fmt:RGB121212_1X36/1920x1080 crop:(0,0)/1920x1080 compose:(0,0)/640x480]"
> + media-ctl -V "'mali-c55 resizer fr':1[fmt:RGB121212_1X36/640x480]"
> + yavta -f RGB565 -s 640x480 -c10 /dev/video0
> +
> +Capturing images in YUV formats
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +If we need to output YUV data rather than RGB the color space conversion block
> +needs to be active, which is achieved by setting MEDIA_BUS_FMT_YUV10_1X30 on the

Is 10 bit required here? (As opposed to the 12 bit before in the
pipeline? is that a limitation on the component?) or is this to match
the desired output format?

> +resizer's source pad. We can then configure a capture format like NV12 (here in
> +its multi-planar variant)
> +
> +.. code-block:: none
> +
> + media-ctl -V "'mali-c55 resizer fr':1[fmt:YUV10_1X30/1920x1080]"
> + yavta -f NV12M -s 1920x1080 -c10 /dev/video0
> +
> +Capturing RGB data from the source and processing it with the resizers
> +----------------------------------------------------------------------
> +
> +The Mali-C55 ISP can work with sensors capable of outputting RGB data. In this
> +case although none of the image quality blocks would be used it can still
> +crop/scale the data in the usual way.
> +
> +To achieve this, the ISP's sink pad's format is set to
> +MEDIA_BUS_FMT_RGB202020_1X60 - this reflects the format that data must be in to
> +work with the ISP. Converting the camera sensor's output to that format is the
> +responsibility of external hardware.
> +
> +In this example we ask the test pattern generator to give us RGB data instead of
> +bayer.
> +
> +.. code-block:: none
> +
> + media-ctl -V "'mali-c55 tpg':0[fmt:RGB202020_1X60/1920x1080]"
> + media-ctl -V "'mali-c55 isp':0[fmt:RGB202020_1X60/1920x1080]"
> +
> +Cropping or scaling the data can be done in exactly the same way as outlined
> +earlier.
> +
> +Capturing raw data from the source and outputting it unmodified
> +-----------------------------------------------------------------
> +
> +The ISP can additionally capture raw data from the source and output it on the
> +full resolution pipe only, completely unmodified. In this case the downscale
> +pipe can still process the data normally and be used at the same time.
> +
> +To configure raw bypass the FR resizer's subdevice's routing table needs to be
> +configured, followed by formats in the appropriate places:
> +
> +.. code-block:: none
> +
> + # We need to configure the routing table for the resizer to use the bypass
> + # path along with set formats on the resizer's bypass sink pad. Doing this
> + # necessitates a single media-ctl command, as multiple calls to the program
> + # reset the routing table.
> + media-ctl -R "'mali-c55 resizer fr'[0/0->1/0[0],2/0->1/0[1]]"\
> + -V "'mali-c55 isp':0[fmt:RGB202020_1X60/1920x1080],"\
> + "'mali-c55 resizer fr':2[fmt:RGB202020_1X60/1920x1080],"\
> + "'mali-c55 resizer fr':1[fmt:RGB202020_1X60/1920x1080]"
> +
> + # Set format on the video device and stream
> + yavta -f RGB565 -s 1920x1080 -c10 /dev/video0
> +
> +References
> +==========
> +.. [1] https://git.linuxtv.org/v4l-utils.git/
> +.. [2] https://git.ideasonboard.org/yavta.git
> +.. [3] https://developer.arm.com/Processors/Mali-C55
> diff --git a/Documentation/admin-guide/media/v4l-drivers.rst b/Documentation/admin-guide/media/v4l-drivers.rst
> index f4bb2605f07e..af033c892808 100644
> --- a/Documentation/admin-guide/media/v4l-drivers.rst
> +++ b/Documentation/admin-guide/media/v4l-drivers.rst
> @@ -17,6 +17,7 @@ Video4Linux (V4L) driver-specific documentation
> imx7
> ipu3
> ivtv
> + mali-c55
> mgb4
> omap3isp
> omap4_camera
> --
> 2.34.1