imx8mm lcdif->dsi->adv7535 no video, no errors

[Marco Felsch]

On 22-08-03, Adam Ford wrote:
> On Wed, Aug 3, 2022 at 7:17 AM Dave Stevenson

...

> > Not meaning to butt in, but I have datasheets for ADV7533 and 7535
> > from previously looking at these chips.
> 
> Thanks for the feedback.
> 
> > Mine fairly plainly states:
> > "The DSI receiver input supports DSI video mode operation only, and
> > specifically, only supports nonburst mode with sync pulses".
> > Non-burst mode meaning that the DSI pixel rate MUST be the same as the
> > HDMI pixel rate.
> 
> Mine also states the DSI source needs to provide correct video timing
> with start and stop sync packets.
> 
> If I remember correctly, it seemed like Marek V wanted the hard coded
> samsung,burst-clock-frequency to go away so the clock frequency could
> be set dynamically.

As previously said, this is something on our TODO list too :) but needs
a bit more infrastructure work.

> I have attempted to do some of this work based on what I am seeing in
> the NXP kernel, and I get get my monitor to sync at some resolutions,
> but the screen is usually all green or all blue, so it's not really a
> success. The clock part appears to be good enough to make the monitor
> see some sort of signal, so I am going to investigate the calculation
> of the rest of the video timings to see if I can fix the color issue.

Please don't pay to much attention to the NXP kernel. No one have a glue
where those porches came from. If I specify the burst-clock-freq. to
445.5 and set the lane number to 4 and hack in the porches values from
NXP, than I get a 720P output too. But this isn't the way to go instead
we should calc the porches settings and the burst-clock-frequency
dynamiclly to provide more than just a few resolutions. But for that we
need a clear understanding of how the ADV is working.

I will prepare a repo to day and will send you a link with the hack
patches in it, so you can test it :)

Regards,
  Marco