linux-kernel - Re: imx8mm lcdif->dsi->adv7535 no video, no errors

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Date:   Thu, 4 Aug 2022 11:57:15 +0200
From:   Marco Felsch <m.felsch@...gutronix.de>
To:     Adam Ford <aford173@...il.com>
Cc:     Dave Stevenson <dave.stevenson@...pberrypi.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        David Airlie <airlied@...ux.ie>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Marek Vasut <marex@...x.de>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Jagan Teki <jagan@...rulasolutions.com>, robert.chiras@....com,
        laurentiu.palcu@....com, NXP Linux Team <linux-imx@....com>,
        Jonas Karlman <jonas@...boo.se>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        arm-soc <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Robert Foss <robert.foss@...aro.org>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Shawn Guo <shawnguo@...nel.org>
Subject: Re: imx8mm lcdif->dsi->adv7535 no video, no errors

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