On 8/13/19 3:55 PM, Sakari Ailus wrote: > When the support for serial busses was introduced in V4L2, it was decided > to use the existing parallel bus media bus pixel codes to describe them. > While this was a practical choice at the time, it necessitates choosing > which one of the many parallel mbus pixel codes to use, for on the serial > busses these formats are effectively all equivalent. > > The practice has always been to use the pixel code that describes a bus > that transfers a single sample per clock. Document this. > > Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx> Acked-by: Hans Verkuil <hverkuil-cisco@xxxxxxxxx> Regards, Hans > --- > since v1: > > - Add an example of mbus pixel codes on serial and parallel busses. > > Documentation/media/kapi/csi2.rst | 7 +++++++ > Documentation/media/uapi/v4l/subdev-formats.rst | 8 ++++++++ > 2 files changed, 15 insertions(+) > > diff --git a/Documentation/media/kapi/csi2.rst b/Documentation/media/kapi/csi2.rst > index a7e75e2eba85a..c67736a15c45b 100644 > --- a/Documentation/media/kapi/csi2.rst > +++ b/Documentation/media/kapi/csi2.rst > @@ -72,3 +72,10 @@ the transmitter up by using the > :c:type:`v4l2_subdev_core_ops`->s_power() callback. This may take > place either indirectly by using :c:func:`v4l2_pipeline_pm_use` or > directly. > + > +Formats > +------- > + > +The media bus pixel codes document parallel formats. Should the pixel data be > +transported over a serial bus, the media bus pixel code that describes a > +parallel format that transfers a sample on a single clock cycle is used. > diff --git a/Documentation/media/uapi/v4l/subdev-formats.rst b/Documentation/media/uapi/v4l/subdev-formats.rst > index ab1a48a5ae80b..7b8e17c7b68b4 100644 > --- a/Documentation/media/uapi/v4l/subdev-formats.rst > +++ b/Documentation/media/uapi/v4l/subdev-formats.rst > @@ -85,6 +85,14 @@ formats in memory (a raw Bayer image won't be magically converted to > JPEG just by storing it to memory), there is no one-to-one > correspondence between them. > > +The media bus pixel codes document parallel formats. Should the pixel data be > +transported over a serial bus, the media bus pixel code that describes a > +parallel format that transfers a sample on a single clock cycle is used. For > +instance, both MEDIA_BUS_FMT_BGR888_1X24 and MEDIA_BUS_FMT_BGR888_3X8 are used > +on parallel busses for transferring an 8 bits per sample BGR data, whereas on > +serial busses the data in this format is only referred to using > +MEDIA_BUS_FMT_BGR888_1X24. This is because there is effectively only a single > +way to transport that format on the serial busses. > > Packed RGB Formats > ^^^^^^^^^^^^^^^^^^ >
