linux-kernel - Re: [PATCH] media: ov8856: Remove 3280x2464 mode

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Date:   Fri, 27 Nov 2020 19:26:35 +0900
From:   Tomasz Figa <tfiga@...omium.org>
To:     Robert Foss <robert.foss@...aro.org>
Cc:     Bingbu Cao <bingbu.cao@...ux.intel.com>,
        Dongchun Zhu <dongchun.zhu@...iatek.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media <linux-media@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Ben Kao <ben.kao@...el.com>
Subject: Re: [PATCH] media: ov8856: Remove 3280x2464 mode

On Thu, Nov 26, 2020 at 7:00 PM Robert Foss <robert.foss@...aro.org> wrote:
>
> On Wed, 25 Nov 2020 at 08:32, Tomasz Figa <tfiga@...omium.org> wrote:
> >
> > Hi Bingbu,
> >
> > On Wed, Nov 25, 2020 at 1:15 PM Bingbu Cao <bingbu.cao@...ux.intel.com> wrote:
> > >
> > >
> > >
> > > On 11/24/20 6:20 PM, Robert Foss wrote:
> > > > On Tue, 24 Nov 2020 at 10:42, Bingbu Cao <bingbu.cao@...ux.intel.com> wrote:
> > > >>
> > > >> Hi, Robert
> > > >>
> > > >> I remember that the full size of ov8856 image sensor is 3296x2480 and we can get the 3280x2464
> > > >> frames based on current settings.
> > > >>
> > > >> Do you have any issues with this mode?
> > > >
> > > > As far as I can tell using the 3280x2464 mode actually yields an
> > > > output resolution that is 3264x2448.
> > > >
> > > > What does your hardware setup look like? And which revision of the
> > > > sensor are you using?
> > > >
> > >
> > > Robert, the sensor revision I am using is v1.1. I just checked the actual output pixels on our
> > > hardware, the output resolution with 2464 mode is 3280x2464, no black pixels.
> > >
> > > As Tomasz said, some ISP has the requirement of extra pixel padding, From the ov8856 datasheet,
> > > the central 3264x2448 pixels are *suggested* to be output from the pixel array and the boundary
> > > pixels can be used for additional processing. In my understanding, the 32 dummy lines are not
> > > black lines.
> >
> > The datasheet says that only 3264x2448 are active pixels. What pixel
> > values are you seeing outside of that central area? In the datasheet,
> > those look like "optically black" pixels, which are not 100% black,
> > but rather as if the sensor cells didn't receive any light - noise can
> > be still there.
> >
>
> I've been developing support for some Qcom ISP functionality, and
> during the course of this I ran into the issue I was describing, where
> the 3280x2464 mode actually outputs 3264x2448.
>
> I can think of two reasons for this, either ISP driver bugs on my end
> or the fact that the sensor is being run outside of the specification
> and which could be resulting in differences between how the ov8856
> sensors behave.

I just confirmed and we're indeed using this mode in a number of our
projects based on the Intel ISP and it seems to be producing a proper
image with all pixels of the 3280x2464 matrix having proper values.
I'm now double checking whether this isn't some processing done by the
ISP, but I suspect the quality would be bad if it stretched the
central 3264x2448 part into the 3280x2464 frame.

Best regards,
Tomasz