media: Documentation: uapi: Add V4L2 ISP documentation

Add userspace documentation for V4L2 ISP generic parameters and
statistics formats.

Reviewed-by: Daniel Scally <dan.scally@ideasonboard.com>
Reviewed-by: Michael Riesch <michael.riesch@collabora.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Tested-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Signed-off-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>

3 files changed, 69 insertions, 0 deletions

diff --git a/Documentation/userspace-api/media/v4l/meta-formats.rst b/Documentation/userspace-api/media/v4l/meta-formats.rst
index d9868ee88a07..7b758ea9eb4a 100644
--- a/Documentation/userspace-api/media/v4l/meta-formats.rst
+++ b/Documentation/userspace-api/media/v4l/meta-formats.rst
@@ -25,3 +25,4 @@ These formats are used for the :ref:`metadata` interface only.
     metafmt-vivid
     metafmt-vsp1-hgo
     metafmt-vsp1-hgt
+    v4l2-isp
diff --git a/Documentation/userspace-api/media/v4l/v4l2-isp.rst b/Documentation/userspace-api/media/v4l/v4l2-isp.rst
new file mode 100644
index 000000000000..facf6dba1ca7
--- /dev/null
+++ b/Documentation/userspace-api/media/v4l/v4l2-isp.rst
@@ -0,0 +1,67 @@
+.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
+
+.. _v4l2-isp:
+
+************************
+Generic V4L2 ISP formats
+************************
+
+Generic ISP formats are metadata formats that define a mechanism to pass ISP
+parameters and statistics between userspace and drivers in V4L2 buffers. They
+are designed to allow extending them in a backward-compatible way.
+
+ISP parameters
+==============
+
+The generic ISP configuration parameters format is realized by a defining a
+single C structure that contains a header, followed by a binary buffer where
+userspace programs a variable number of ISP configuration data block, one for
+each supported ISP feature.
+
+The :c:type:`v4l2_isp_params_buffer` structure defines the buffer header which
+is followed by a binary buffer of ISP configuration data. Userspace shall
+correctly populate the buffer header with the generic parameters format version
+and with the size (in bytes) of the binary data buffer where it will store the
+ISP blocks configuration.
+
+Each *ISP configuration block* is preceded by an header implemented by the
+:c:type:`v4l2_isp_params_block_header` structure, followed by the configuration
+parameters for that specific block, defined by the ISP driver specific data
+types.
+
+Userspace applications are responsible for correctly populating each block's
+header fields (type, flags and size) and the block-specific parameters.
+
+ISP block enabling, disabling and configuration
+-----------------------------------------------
+
+When userspace wants to configure and enable an ISP block it shall fully
+populate the block configuration and set the V4L2_ISP_PARAMS_FL_BLOCK_ENABLE
+bit in the block header's `flags` field.
+
+When userspace simply wants to disable an ISP block the
+V4L2_ISP_PARAMS_FL_BLOCK_DISABLE bit should be set in block header's `flags`
+field. Drivers accept a configuration parameters block with no additional
+data after the header in this case.
+
+If the configuration of an already active ISP block has to be updated,
+userspace shall fully populate the ISP block parameters and omit setting the
+V4L2_ISP_PARAMS_FL_BLOCK_ENABLE and V4L2_ISP_PARAMS_FL_BLOCK_DISABLE bits in the
+header's `flags` field.
+
+Setting both the V4L2_ISP_PARAMS_FL_BLOCK_ENABLE and
+V4L2_ISP_PARAMS_FL_BLOCK_DISABLE bits in the flags field is not allowed and
+returns an error.
+
+Extension to the parameters format can be implemented by adding new blocks
+definition without invalidating the existing ones.
+
+ISP statistics
+==============
+
+Support for generic statistics format is not yet implemented in Video4Linux2.
+
+V4L2 ISP uAPI data types
+========================
+
+.. kernel-doc:: include/uapi/linux/media/v4l2-isp.h
diff --git a/MAINTAINERS b/MAINTAINERS
index 97c8a4cdbc2c..a22249166e4a 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -26889,6 +26889,7 @@ V4L2 GENERIC ISP PARAMETERS AND STATISTIC FORMATS
 M:	Jacopo Mondi <jacopo.mondi@ideasonboard.com>
 L:	linux-media@vger.kernel.org
 S:	Maintained
+F:	Documentation/userspace-api/media/v4l/v4l2-isp.rst
 F:	include/uapi/linux/media/v4l2-isp.h
 
 VF610 NAND DRIVER