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

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Date:   Wed, 2 Oct 2019 07:40:54 -0500
From:   Benoit Parrot <bparrot@...com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>
CC:     Jacopo Mondi <jacopo@...ndi.org>,
        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

Sakari Ailus <sakari.ailus@...ux.intel.com> wrote on Wed [2019-Oct-02 15:35:13 +0300]:
> Hi Benoit,
> 
> On Wed, Oct 02, 2019 at 07:14:38AM -0500, Benoit Parrot wrote:
> > 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.
> 
> It shouldn't make a difference which one you use; if you know the bus type
> (and if it's CSI-2 with D-PHY, number of lanes and how many bits per pixel
> the media bus format has), you can convert fairly trivially between the
> two.

Sakari,

Yes I get that, but at this point as they say I will leave that as an
exercise to the reader...

Benoit

> 
> -- 
> Sakari Ailus
> sakari.ailus@...ux.intel.com