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 :)

Yes indeed, the discussion thread I linked here was mostly interesting
because Hugues tried to do the same for LINK_FREQ iirc, and there
where some usefult pointers.

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.

As reported by Hugues findings, the PLL calculation procedure might be
faulty, and the actuall frequencies on the bus are different from the
calculated ones.

I wish I had more time to re-look at that, as they worked for my and
Sam's use case, but deserve some rework.

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

It seems to me you're reporting a fixed rate. It might make your
receiver happy, but does not report what is acutally put on the bus.
Am I missing something ?

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

As Sakari pointed out, going from one to the other is trivial and
could be done on top.

Thanks
   j

Regard,
Benoit

Jacopo Mondi [off-list ref] wrote on Wed [2019-Oct-02 09:59:51 +0200]:

quoted

Hi Benoit,
  +Hugues

If you're considering an helper, this thread might be useful to you:
https://patchwork.kernel.org/patch/11019673/

Thanks
   j