Re: [PATCH] media: ov5675: use group write to update digital gain

Sakari Ailus
2022-01-10T11:32:52Z

On Wed, Dec 29, 2021 at 10:00:43AM +0000, Cao, Bingbu wrote:
> Hi Sakari,
>
> Thanks for your review.
>
> ________________________
> BRs,
> Bingbu Cao
>
> > -----Original Message-----
> > From: Sakari Ailus <sakari.ailus@linux.intel.com>
> > Sent: Wednesday, December 29, 2021 5:42 PM
> > To: Cao, Bingbu <bingbu.cao@intel.com>
> > Cc: linux-media@vger.kernel.org; Tu, ShawnX <shawnx.tu@intel.com>;
> > senozhatsky@chromium.org; tfiga@chromium.org; bingbu.cao@linux.intel.com;
> > Yeh, Andy <andy.yeh@intel.com>
> > Subject: Re: [PATCH] media: ov5675: use group write to update digital
> > gain
> >
> > Hi Bingbu,
> >
> > On Wed, Dec 29, 2021 at 04:57:39PM +0800, Bingbu Cao wrote:
> > > MWB gain register are used to set gain for each mwb channel mannually.
> > > However, it will involve some artifacts at low light environment as
> > > gain cannot be applied to each channel synchronously. Update the
> > > driver to use group write for digital gain to make the sure RGB
> > > digital gain be applied together at frame boundary.
> >
> > How about the analogue gain and exposure time?
> >
> > Shouldn't they be applied similarly as well? Adding two more writes
> > increases the probability of missing a frame there.
>
> We did not meet issue related to analog gain as the it was applied by only
> 1 reg write, it looks like same issue we found on ov8856, changing to set
> digital gain by only 1 global gain write will fix the problem.

That device is different in its support for global digital gain. This patch
sets the gain for each component separately.

Adding more writes on a given frame increases the probability of slipping
to the following frame. Doing the exposure and gain updates in the same
group write would alleviate that a little.

>
> >
> > This is of course a trick since the control framework doesn't really
> > support this, but I think this support should be added.
> >
> > --
> > Regards,
> >
> > Sakari Ailus

--
Sakari Ailus