[PATCH v13 11/15] Documentation: mali-c55: Add Statistics documentation

[Daniel Scally <dan.scally@ideasonboard.com>]

Add documentation explaining the ability to capture statistics from
the mali-c55 driver's new V4L2 device, as well as the various tap
points from which those statistics can be drawn in the ISP's
processing flow. Additionally add a page detailing the new V4L2
meta format for the mali-c55 statistics.

Tested-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Nayden Kanchev  <nayden.kanchev@arm.com>
Co-developed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Signed-off-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Signed-off-by: Daniel Scally <dan.scally@ideasonboard.com>
---
Changes in v12:

        - Fix reference

Changes in v11:

        - None

Changes in v10:

	- None

Changes in v9:

	- None

Changes in v8:

	- None

Changes in v7:

	- None

Changes in v6:

	- None

Changes in v5:

	- New patch
---
 Documentation/admin-guide/media/mali-c55.rst       | 60 +++++++++++++++++++++-
 .../userspace-api/media/v4l/meta-formats.rst       |  1 +
 .../media/v4l/metafmt-arm-mali-c55.rst             | 29 +++++++++++
 MAINTAINERS                                        |  1 +
 4 files changed, 90 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/media/mali-c55.rst b/Documentation/admin-guide/media/mali-c55.rst
index 72cdded507b3a7918e28d9bd9a1c6f72ddf9e664..03723e0e8e43f17a04ede0032b2ddbfdb859d1e3 100644
--- a/Documentation/admin-guide/media/mali-c55.rst
+++ b/Documentation/admin-guide/media/mali-c55.rst
@@ -67,10 +67,11 @@ The driver has 4 V4L2 subdevices:
 - `mali_c55 resizer fr`: The Full-Resolution pipe resizer
 - `mali_c55 resizer ds`: The Downscale pipe resizer
 
-The driver has 2 V4L2 video devices:
+The driver has 3 V4L2 video devices:
 
 - `mali-c55 fr`: The full-resolution pipe's capture device
 - `mali-c55 ds`: The downscale pipe's capture device
+- `mali-c55 3a stats`: The 3A statistics capture device
 
 Frame sequences are synchronised across to two capture devices, meaning if one
 pipe is started later than the other the sequence numbers returned in its
@@ -333,6 +334,63 @@ configured, followed by formats in the appropriate places:
     # Set format on the video device and stream
     yavta -f RGB565 -s 1920x1080 -c10 /dev/video0
 
+.. _mali-c55-3a-stats:
+
+Capturing ISP Statistics
+========================
+
+The ISP is capable of producing statistics for consumption by image processing
+algorithms running in userspace. These statistics can be captured by queueing
+buffers to the `mali-c55 3a stats` V4L2 Device whilst the ISP is streaming. Only
+the :ref:`V4L2_META_FMT_MALI_C55_STATS <v4l2-meta-fmt-mali-c55-stats>`
+format is supported, so no format-setting need be done:
+
+.. code-block:: none
+
+    # We assume the media graph has been configured to support RGB565 capture
+    # from the mali-c55 fr V4L2 Device, which is at /dev/video0. The statistics
+    # V4L2 device is at /dev/video3
+
+    yavta -f RGB565 -s 1920x1080 -c32 /dev/video0 && \
+    yavta -c10 -F /dev/video3
+
+The layout of the buffer is described by :c:type:`mali_c55_stats_buffer`,
+but broadly statistics are generated to support three image processing
+algorithms; AEXP (Auto-Exposure), AWB (Auto-White Balance) and AF (Auto-Focus).
+These stats can be drawn from various places in the Mali C55 ISP pipeline, known
+as "tap points". This high-level block diagram is intended to explain where in
+the processing flow the statistics can be drawn from::
+
+                  +--> AEXP-2            +----> AEXP-1          +--> AF-0
+                  |                      +----> AF-1            |
+                  |                      |                      |
+      +---------+ |   +--------------+   |   +--------------+   |
+      |  Input  +-+-->+ Digital Gain +---+-->+ Black Level  +---+---+
+      +---------+     +--------------+       +--------------+       |
+  +-----------------------------------------------------------------+
+  |
+  |   +--------------+ +---------+       +----------------+
+  +-->| Sinter Noise +-+  White  +--+--->|  Lens Shading  +--+---------------+
+      |   Reduction  | | Balance |  |    |                |  |               |
+      +--------------+ +---------+  |    +----------------+  |               |
+                                    +---> AEXP-0 (A)         +--> AEXP-0 (B) |
+  +--------------------------------------------------------------------------+
+  |
+  |   +----------------+      +--------------+  +----------------+
+  +-->|  Tone mapping  +-+--->| Demosaicing  +->+ Purple Fringe  +-+-----------+
+      |                | |    +--------------+  |   Correction   | |           |
+      +----------------+ +-> AEXP-IRIDIX        +----------------+ +---> AWB-0 |
+  +----------------------------------------------------------------------------+
+  |                    +-------------+        +-------------+
+  +------------------->|   Colour    +---+--->|    Output   |
+                       | Correction  |   |    |  Pipelines  |
+                       +-------------+   |    +-------------+
+                                         +-->  AWB-1
+
+At present all statistics are drawn from the 0th tap point for each algorithm;
+I.E. AEXP statistics from AEXP-0 (A), AWB statistics from AWB-0 and AF
+statistics from AF-0. In the future this will be configurable.
+
 References
 ==========
 .. [1] https://git.linuxtv.org/v4l-utils.git/
diff --git a/Documentation/userspace-api/media/v4l/meta-formats.rst b/Documentation/userspace-api/media/v4l/meta-formats.rst
index 7b758ea9eb4ac3c4b354bf8e2f319985ed9e2b37..3e0cab153f0ac5e6d76696c5b78eebb0db43b354 100644
--- a/Documentation/userspace-api/media/v4l/meta-formats.rst
+++ b/Documentation/userspace-api/media/v4l/meta-formats.rst
@@ -13,6 +13,7 @@ These formats are used for the :ref:`metadata` interface only.
 .. toctree::
     :maxdepth: 1
 
+    metafmt-arm-mali-c55
     metafmt-c3-isp
     metafmt-d4xx
     metafmt-generic
diff --git a/Documentation/userspace-api/media/v4l/metafmt-arm-mali-c55.rst b/Documentation/userspace-api/media/v4l/metafmt-arm-mali-c55.rst
new file mode 100644
index 0000000000000000000000000000000000000000..0bda9740a6be20df541ac7cf78e45e510f79ad19
--- /dev/null
+++ b/Documentation/userspace-api/media/v4l/metafmt-arm-mali-c55.rst
@@ -0,0 +1,29 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+.. _v4l2-meta-fmt-mali-c55-stats:
+
+*************************************
+V4L2_META_FMT_MALI_C55_STATS ('C55S')
+*************************************
+
+3A Statistics
+=============
+
+The ISP device collects different statistics over an input bayer frame. Those
+statistics can be obtained by userspace from the
+:ref:`mali-c55 3a stats <mali-c55-3a-stats>` metadata capture video node, using
+the :c:type:`v4l2_meta_format` interface. The buffer contains a single instance
+of the C structure :c:type:`mali_c55_stats_buffer` defined in
+``mali-c55-config.h``, so the structure can be obtained from the buffer by:
+
+.. code-block:: C
+
+	struct mali_c55_stats_buffer *stats =
+		(struct mali_c55_stats_buffer *)buf;
+
+For details of the statistics see :c:type:`mali_c55_stats_buffer`.
+
+Arm Mali-C55 uAPI data types
+============================
+
+.. kernel-doc:: include/uapi/linux/media/arm/mali-c55-config.h
diff --git a/MAINTAINERS b/MAINTAINERS
index e7b1b3458854a764ef94bed30ed518256ac2bca6..f7bc74181fa4d2f8bfa9022ea85f94fbb01ff62d 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2115,6 +2115,7 @@ F:	Documentation/admin-guide/media/mali-c55-graph.dot
 F:	Documentation/admin-guide/media/mali-c55.rst
 F:	Documentation/devicetree/bindings/media/arm,mali-c55.yaml
 F:	Documentation/userspace-api/media/drivers/mali-c55.rst
+F:	Documentation/userspace-api/media/v4l/metafmt-arm-mali-c55.rst
 F:	drivers/media/platform/arm/mali-c55/
 F:	include/uapi/linux/media/arm/mali-c55-config.h
 

-- 
2.43.0