linux-kernel - Re: [Patch 1/3] media: ov5640: add PIXEL

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Message-ID: <20191002121438.g3re6v54q4hit2wv@ti.com>
Date:   Wed, 2 Oct 2019 07:14:38 -0500
From:   Benoit Parrot <bparrot@...com>
To:     Jacopo Mondi <jacopo@...ndi.org>
CC:     Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Hans Verkuil <hverkuil@...all.nl>,
        <linux-media@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <hugues.fruchet@...com>
Subject: Re: [Patch 1/3] media: ov5640: add PIXEL_RATE control

Hi Jacopo,

Maybe, I miss spoke when I mentioned a helper I did not intent a framework
level generic function. Just a function to help in this case :)

That being said, I re-read the thread you mentioned. And as Hughes pointed
out dynamically generating a "working" link frequency value which can be
used by a CSI2 receiver to properly configure its PHY is not trivial.

When I created this patch, I also had another to add V4L2_CID_LINK_FREQ
support. I am testing this against the TI CAL CSI2 receiver, which already
uses the V4L2_CID_PIXEL_RATE value for that purpose, so I also had a patch
to add support for V4L2_CID_LINK_FREQ to that driver as well.

Unfortunately, similar to Hughes' findings I was not able to make it "work"
with all supported resolution/framerate.

Unlike my V4L2_CID_PIXEL_RATE solution which now works in all mode with the
same receiver.

So long story short I dropped the V4L2_CID_LINK_FREQ patch and focused on
V4L2_CID_PIXEL_RATE instead.

Regard,
Benoit

Jacopo Mondi <jacopo@...ndi.org> wrote on Wed [2019-Oct-02 09:59:51 +0200]:
> Hi Benoit,
>   +Hugues
> 
> If you're considering an helper, this thread might be useful to you:
> https://patchwork.kernel.org/patch/11019673/
> 
> Thanks
>    j
>