imx8mp: HDMI display blank/black problems

[Frieder Schrempf]

Hi Johannes,

On 25.10.24 10:05 AM, mailinglist1 at johanneskirchmair.de wrote:
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> Hey,
> We had some problems with the hdmi on the imx8mp and wanted to leave, what we found out about it, somewhere for others to find it.
> 
> The problem was that our hdmi display sometimes stayed blank after hot plugging and sometimes at startup. On older kernel versions 6.6 we did not have the problem with the not mainlined hdmi patches.
> We tracked the commit down that introduced the problem for us. It was the following “driver core: Enable fw_devlink=rpm by default”  https://lore.kernel.org/lkml/20231113220948.80089-1-saravanak@google.com/
> So we switched back to FW_DEVLINK_FLAGS_ON via kernel parameter. Don’t really understand what the problem with RPM is.
> 
> So, this information is just for reference. Maybe someone has an idea what is going on here. And how to fix the problem in a more proper way.

Thanks for investigating and sharing your results!

I'm seeing the same symptoms and previously found out that this is
related to LCDIF underrun errors. See [1] for more information.

Adam has also started this thread: [2].

Anyway, knowing that this is related to fw_devlink=rpm is really
helpful. I just tried with fw_devlink=on and wasn't able to see any
issues anymore. So this confirms your findings.

I hope that some of the driver framework and runtime PM experts can help
to find out what is actually wrong and how the correct fix might look like.

I'm also CC-ing Saravana who authored the change from fw_devlink=on to
fw_devlink=rpm to see if they have anything to add.

Thanks
Frieder

[1]
https://patchwork.kernel.org/project/linux-phy/cover/20240904233100.114611-1-aford173@gmail.com/#26014057
[2]
https://lore.kernel.org/imx/8cfd3052-c85a-4235-b9b8-6d2929e9e455@kontron.de/T/