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

[Bingbu Cao <bingbu.cao@linux.intel.com>]

On 1/10/22 7:32 PM, Sakari Ailus wrote:
> 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.

Sakari,

It is feasible to put the exposure and gain update in a same group, however, lunching
the group at different time may increase the probability of slipping as well.

What do you think?

> 
>>
>>>
>>> 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
> 

-- 
Best regards,
Bingbu Cao