Re: [PATCH 4/6] media: ti: cal: use CSI-2 frame number for seq number

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

Hi Tomi,

On Fri, Apr 22, 2022 at 09:41:51AM +0300, Tomi Valkeinen wrote:
> On 22/04/2022 02:52, Laurent Pinchart wrote:
> > On Thu, Apr 21, 2022 at 05:34:47PM +0300, Tomi Valkeinen wrote:
> >> The userspace needs a way to match received metadata buffers to pixel
> >> data buffers. The obvious way to do this is to use the CSI-2 frame
> >> number, as both the metadata and the pixel data have the same frame
> >> number as they come from the same frame.
> >>
> >> However, we don't have means to convey the frame number to userspace. We
> >> do have the 'sequence' field, which with a few tricks can be used for
> >> this purpose.
> >>
> >> To achieve this, track the frame number for each virtual channel and
> >> increase the sequence for each virtual channel by frame-number -
> >> previous-frame-number, also taking into account the eventual wrap of the
> >> CSI-2 frame number.
> >>
> >> This way we get a monotonically increasing sequence number which is
> >> common to all streams using the same virtual channel.
> > 
> > I'd agree in principle, if it wasn't for the fact that sensors are not
> > required to produce a frame number :-S
> 
> In that case the CAL hardware will increment the register every frame. 
>  From CAL doc:
> 
> Frame number.
> Matches the frame number sent by the camera when the
> camera transmits it.
> Otherwise, incremented by one on every FS short packet
> for this context.

Is that only when the FS packet contains a frame number equal to 0 ? How
about the extreme case where the frame number counts up to 2 and resets
to 1, effectively toggling between 1 and 2 ? Does your patch support
this correctly ?

> Reset when the context is enabled.
> 
> I'll add a note about that to the desc.

-- 
Regards,

Laurent Pinchart