[PATCH 2/6] media: Documentation: uapi: Update V4L2 ISP for extensible stats

[Jacopo Mondi]

From: Antoine Bouyer <antoine.bouyer@xxxxxxx>

Rework the userspace-api documentation of V4L2 ISP to support
statistics.

Update all occurences of 'v4l2_isp_param' types to match the uAPI
changes and add a section to document the statistics serialization
format.

Signed-off-by: Antoine Bouyer <antoine.bouyer@xxxxxxx>
[Update on uAPI changes]
Signed-off-by: Jacopo Mondi <jacopo.mondi@xxxxxxxxxxxxxxxx>
---
 Documentation/userspace-api/media/v4l/v4l2-isp.rst | 45 ++++++++++++++++------
 1 file changed, 34 insertions(+), 11 deletions(-)

diff --git a/Documentation/userspace-api/media/v4l/v4l2-isp.rst b/Documentation/userspace-api/media/v4l/v4l2-isp.rst
index facf6dba1ca7..8a3f05b5e85f 100644
--- a/Documentation/userspace-api/media/v4l/v4l2-isp.rst
+++ b/Documentation/userspace-api/media/v4l/v4l2-isp.rst
@@ -18,22 +18,22 @@ 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
+The :c:type:`v4l2_isp_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 serialization 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 a header implemented by the
+:c:type:`v4l2_isp_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
------------------------------------------------
+ISP parameters 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
@@ -59,7 +59,30 @@ definition without invalidating the existing ones.
 ISP statistics
 ==============
 
-Support for generic statistics format is not yet implemented in Video4Linux2.
+The generic ISP statistics format is identical to the generic ISP configuration
+parameters format. It is realized by defining a C structure that contains a
+header, followed by binary buffer where the ISP driver copies a variable number
+of ISP statistics blocks.
+
+Extensible statistics buffers have :c:type:`v4l2_isp_buffer` header followed by
+a binary buffer of ISP statistics data. ISP drivers populate the buffer header
+with the serialization format version and with the size (in bytes) of the binary
+data buffer where ISP statistics data are serialized. Applications shall
+validate that the serialization format version matches the expected one and that
+the buffer size doesn't exceed the maximum size for a statistics buffer as
+declared by the driver's uAPI header.
+
+Each *ISP statistics block* is preceded by a header implemented by the
+:c:type:`v4l2_isp_block_header` structure, followed by the statistics data for
+that specific block. The driver might optionally report platform-specific flags
+associated with each statistics block.
+
+Applications inspect the statistics block type as reported in the header and
+validates the reported size matches the block's expected size before accessing
+the ISP statistics data.
+
+Extension to the statistics format can be implemented by adding new blocks
+definition without invalidating the existing ones.
 
 V4L2 ISP uAPI data types
 ========================

-- 
2.53.0