Re: [PATCH] media: video-i2c: add mlx90640 subpage data to output

[Matt Ranostay <matt.ranostay@konsulko.com>]

On Mon, Aug 12, 2019 at 6:05 AM Hans Verkuil <hverkuil@xs4all.nl> wrote:
>
> Hi Matt,
>
> On 8/11/19 9:10 AM, Matt Ranostay wrote:
> > Add current subpage data via the status register to the video
> > frame in the last word of data, which seems to be unused
> > undocumented reserved data.
>
> I don't really understand from this description what is going on
> here.
>
> mlx90640_xfer() reads the buffer data from the i2c device, but
> that data is split over two different addresses? Or does
> 0x8000 contain something else with a different meaning compared
> to what is read from 0x400?

So the status register contains the bit on if subpage one or two is in
the reading, so in reality a 8 fps reading in v4l2
space is only a 4 fps processed images.

This is important for userspace processing because it needs to know it
has a subpage one and two to process the thermal data.
Can't do it with subpage two and one in that order per the algorithms,
and also since it is polling it is possible a frame will be dropped.

- Matt

>
> >
> > Signed-off-by: Matt Ranostay <matt.ranostay@konsulko.com>
> > ---
> >  drivers/media/i2c/video-i2c.c | 12 ++++++++++--
> >  1 file changed, 10 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/media/i2c/video-i2c.c b/drivers/media/i2c/video-i2c.c
> > index 078141712c88..8bc7b228ba40 100644
> > --- a/drivers/media/i2c/video-i2c.c
> > +++ b/drivers/media/i2c/video-i2c.c
> > @@ -168,8 +168,16 @@ static int amg88xx_xfer(struct video_i2c_data *data, char *buf)
> >
> >  static int mlx90640_xfer(struct video_i2c_data *data, char *buf)
> >  {
> > -     return regmap_bulk_read(data->regmap, 0x400, buf,
> > -                             data->chip->buffer_size);
> > +     int ret = regmap_bulk_read(data->regmap, 0x400, buf,
> > +                                data->chip->buffer_size);
>
> Shouldn't this be data->chip->buffer_size - size, since the last
> 'size' bytes will be overwritten anyway?
>
> > +     int size = data->chip->bpp / 8;
> > +
> > +     if (ret)
> > +             return ret;
> > +
> > +     /* read status register, which contains subpage that is read */
> > +     return regmap_bulk_read(data->regmap, 0x8000,
> > +                             &buf[data->chip->buffer_size - size], size);
> >  }
> >
> >  static int amg88xx_setup(struct video_i2c_data *data)
> >
>
> Regards,
>
>         Hans