Re: [PATCH WIP RFC v2 0/2] media: uapi: Add V4L2_CID_VTOTAL control

[Sakari Ailus]

Hi Nicolas, Benjamin,

On Thu, Jun 22, 2023 at 11:14:41AM -0400, Nicolas Dufresne wrote:
> Hi,
> 
> Le jeudi 22 juin 2023 à 09:12 +0200, Benjamin Bara a écrit :
> > Hi!
> > 
> > This series adds new controls for the vertical and horizontal total
> > size. Camera sensors usually have registers regarding the total size and
> > not the blanking size. Also user space prefers to calculate with total
> > frame sizes. Therefore, this would simplify implementations on both
> > sides and could be seen as a replacement or upgrade for V4L2_CID_VBLANK.
> > Additionally, its value is independent from format changes and therefore
> > simplifies calculations in user space.
> 
> The naming is getting more and more generic. We need to find a way to give these
> controls a name that associates them to their usage field (sensors). If we keep
> growing the control list this way, in few years it will be terribly hard to
> understand what is used for what.
> 
> What about, V4L2_CID_SENSOR_VTOTAL/HTOTAL ? I'm expecting the last bit of the
> name to come from very well known specification, otherwise, its not a great name
> either in my opinion.

These controls can, in theory at least, be used for any image data bus:
they're not related to sensors but to any source of image data on a bus.
Compare this to the LINK_FREQ control, for instance: you basically need
these to calculate the frame rate (or calculate these based on the desired
frame rate).

These configurations are often called line length (in) pixels and frame
length (in) lines, the controls could be thus V4L2_CID_LLP and
V4L2_CID_FLL, to keep them a little bit shorter.

-- 
Regards,

Sakari Ailus