Re: [PATCH v3 09/10] media: Add media bus codes for MIPI CCS embedded data

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

On Wed, Sep 06, 2023 at 01:03:18PM +0000, Sakari Ailus wrote:
> On Tue, Sep 05, 2023 at 08:25:35PM +0300, Laurent Pinchart wrote:
> > On Tue, Aug 08, 2023 at 10:55:37AM +0300, Sakari Ailus wrote:
> > > Add new MIPI CCS embedded data media bus formats.
> > > 
> > > Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> > > ---
> > >  .../media/v4l/subdev-formats.rst              | 32 +++++++++++++++++++
> > >  include/uapi/linux/media-bus-format.h         | 10 +++++-
> > >  2 files changed, 41 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/Documentation/userspace-api/media/v4l/subdev-formats.rst b/Documentation/userspace-api/media/v4l/subdev-formats.rst
> > > index c615da08502d..5d5407738af9 100644
> > > --- a/Documentation/userspace-api/media/v4l/subdev-formats.rst
> > > +++ b/Documentation/userspace-api/media/v4l/subdev-formats.rst
> > > @@ -8491,3 +8491,35 @@ and finally the bit number in subscript. "p" indicates a padding bit.
> > >        - p
> > >        - p
> > >        - p
> > > +
> > > +MIPI CCS Embedded Data Formats
> > > +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > > +
> > > +`MIPI CCS <https://www.mipi.org/specifications/camera-command-set>`_ defines an
> > 
> > s/an$/a/
> 
> Yes. I think I had "embedded" there in the past...
> 
> > > +metadata format for sensor embedded data, which is used to store the register
> > > +configuration used for capturing a given frame. The format is defined in the CCS
> > > +specification.
> > 
> > Strictly speaking, the MIPI CCS embedded data format specifies not just
> > the data packing (insertion of padding bytes) and the data encoding (the
> > data format byte and the tag codes), but also the register addresses and
> > values that are reported in the embedded data. Do you envision the media
> > bus formats defined here as being applicable to sensors that use the
> > same packing and encoding as CCS, but different registers, or only to
> > fully compliant CCS sensors ?
> 
> There are sensors that aren't fully compatible with CCS (including those
> compatible with SMIA and SMIA++) but I wouldn't expect the format to be
> used by devices that are entirely incompatible with CCS.

So if a sensor uses the same packing and encoding as CCS, but a
different register set, you would require other media bus codes ? If so,
how would you require those media bus codes to be documented ? The
packing and encoding could be documented as being identical to CCS, but
what about the data itself ? Would you require the datasheet to be
public ? Or the entire register set being documented in the V4L2 spec ?

-- 
Regards,

Laurent Pinchart