media: media/doc: Allow sizeimage to be set by v4l clients

This changes v4l2_pix_format and v4l2_plane_pix_format sizeimage
field description to allow v4l clients to set bigger image size
in case of variable length compressed data.

Presently s5p-mfc and mtk-vcodec codec drivers use that. Lets
make it obvious in the documentation.

Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

1 files changed, 12 insertions, 1 deletions

diff --git a/Documentation/media/uapi/v4l/pixfmt-v4l2.rst b/Documentation/media/uapi/v4l/pixfmt-v4l2.rst
index 71eebfc6d853..da6da2ef139a 100644
--- a/Documentation/media/uapi/v4l/pixfmt-v4l2.rst
+++ b/Documentation/media/uapi/v4l/pixfmt-v4l2.rst
@@ -89,7 +89,18 @@ Single-planar format structure
       - Size in bytes of the buffer to hold a complete image, set by the
 	driver. Usually this is ``bytesperline`` times ``height``. When
 	the image consists of variable length compressed data this is the
-	maximum number of bytes required to hold an image.
+	number of bytes required by the codec to support the worst-case
+	compression scenario.
+
+	The driver will set the value for uncompressed images.
+
+	Clients are allowed to set the sizeimage field for variable length
+	compressed data flagged with ``V4L2_FMT_FLAG_COMPRESSED`` at
+	:ref:`VIDIOC_ENUM_FMT`, but the driver may ignore it and set the
+	value itself, or it may modify the provided value based on
+	alignment requirements or minimum/maximum size requirements.
+	If the client wants to leave this to the driver, then it should
+	set sizeimage to 0.
     * - __u32
       - ``colorspace``
       - Image colorspace, from enum :c:type:`v4l2_colorspace`.