linux-kernel - Re: [PATCH] media: i2c: vgxy61: Report stream using frame descriptors

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Message-ID: <aK2Ft4ODOF2EPgld@kekkonen.localdomain>
Date: Tue, 26 Aug 2025 13:00:23 +0300
From: Sakari Ailus <sakari.ailus@...ux.intel.com>
To: Julien Massot <julien.massot@...labora.com>
Cc: kernel@...labora.com, Benjamin Mugnier <benjamin.mugnier@...s.st.com>,
	Sylvain Petinot <sylvain.petinot@...s.st.com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: i2c: vgxy61: Report stream using frame descriptors

Hi Julien,

On Tue, Aug 26, 2025 at 09:21:29AM +0200, Julien Massot wrote:
> Hi Sakari,
> 
> On Fri, 2025-08-15 at 06:04 +0000, Sakari Ailus wrote:
> > Hi Julien,
> > 
> > On Fri, Jul 04, 2025 at 11:28:24AM +0200, Julien Massot wrote:
> > > Add support for .get_frame_desc() to report CSI-2 virtual channel
> > > and data type information. This allows CSI-2 receivers to properly
> > > interpret the stream without inferring the data type from the pixel
> > > format.
> > > 
> > > Signed-off-by: Julien Massot <julien.massot@...labora.com>
> > > ---
> > >  drivers/media/i2c/vgxy61.c | 16 ++++++++++++++++
> > >  1 file changed, 16 insertions(+)
> > > 
> > > diff --git a/drivers/media/i2c/vgxy61.c b/drivers/media/i2c/vgxy61.c
> > > index
> > > 5b0479f3a3c0592be430cefe5a1ab9a76812ba84..44d6c8d8fbf8d6182e42d44e129b
> > > c45945ee0da5 100644
> > > --- a/drivers/media/i2c/vgxy61.c
> > > +++ b/drivers/media/i2c/vgxy61.c
> > > @@ -1181,6 +1181,21 @@ static int vgxy61_s_stream(struct v4l2_subdev
> > > *sd, int enable)
> > >  	return ret;
> > >  }
> > >  
> > > +static int vgxy61_get_frame_desc(struct v4l2_subdev *sd, unsigned int
> > > pad,
> > > +				 struct v4l2_mbus_frame_desc *fd)
> > > +{
> > > +	struct vgxy61_dev *sensor = to_vgxy61_dev(sd);
> > > +
> > > +	fd->type = V4L2_MBUS_FRAME_DESC_TYPE_CSI2;
> > > +	fd->num_entries = 1;
> > > +	fd->entry[0].pixelcode = sensor->fmt.code;
> > > +	fd->entry[0].stream = 0;
> > > +	fd->entry[0].bus.csi2.vc = 0;
> > > +	fd->entry[0].bus.csi2.dt = get_data_type_by_code(sensor-
> > > >fmt.code);
> > > +
> > > +	return 0;
> > > +}
> > > +
> > >  static int vgxy61_set_fmt(struct v4l2_subdev *sd,
> > >  			  struct v4l2_subdev_state *sd_state,
> > >  			  struct v4l2_subdev_format *format)
> > > @@ -1402,6 +1417,7 @@ static const struct v4l2_subdev_pad_ops
> > > vgxy61_pad_ops = {
> > >  	.set_fmt = vgxy61_set_fmt,
> > >  	.get_selection = vgxy61_get_selection,
> > >  	.enum_frame_size = vgxy61_enum_frame_size,
> > > +	.get_frame_desc = vgxy61_get_frame_desc,
> > >  };
> > >  
> > >  static const struct v4l2_subdev_ops vgxy61_subdev_ops = {
> > > 
> > 
> > I guess this is correct as such, but does it provide any information
> > that
> > isn't already available? I.e. I wouldn't add it just for the sake of it.
> Perhaps, I missed something. Without the get_frame_desc the CSI receiver
> have to infers the datatype based on the pixel format.

I think we should have a function in the framework to do that. Oh, we
actually already do have the function, call_get_mbus_config(), it just
doesn't get the format yet. Currently receiver drivers handle this by
themselves but that doesn't scale very well.

> 
> I made this patch because some CSI receivers, such as the upcoming GMSL2
> framework are relying on the frame desc to update its routing table.
> So, it will only support sensors implementing the get_frame_desc function.

-- 
Regards,

Sakari Ailus