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

From: Marco Felsch <m.felsch@pengutronix.de>
To: Adam Ford <aford173@gmail.com>
Cc: Dave Stevenson <dave.stevenson@raspberrypi.com>,
	Neil Armstrong <narmstrong@baylibre.com>,
	David Airlie <airlied@linux.ie>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
	Andrzej Hajda <andrzej.hajda@intel.com>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Marek Vasut <marex@denx.de>,
	Jernej Skrabec <jernej.skrabec@gmail.com>,
	Jagan Teki <jagan@amarulasolutions.com>,
	robert.chiras@nxp.com, laurentiu.palcu@nxp.com,
	NXP Linux Team <linux-imx@nxp.com>,
	Jonas Karlman <jonas@kwiboo.se>,
	Sascha Hauer <s.hauer@pengutronix.de>,
	arm-soc <linux-arm-kernel@lists.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Robert Foss <robert.foss@linaro.org>,
	Pengutronix Kernel Team <kernel@pengutronix.de>,
	Shawn Guo <shawnguo@kernel.org>
Subject: Re: imx8mm lcdif->dsi->adv7535 no video, no errors
Date: Thu, 4 Aug 2022 11:57:15 +0200	[thread overview]
Message-ID: <20220804095715.d3ay7yvn2adxdo4x@pengutronix.de> (raw)
In-Reply-To: <CAHCN7x+HSPJpYYDgV_F91ZsPHW9Uwze8KRAqWE-XAyp5yzB9Hw@mail.gmail.com>

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