drm/vc4: Limits fkms to modes <= 85Hz

[alanbork]

Because of commit 883a1a5, the pi4 now ignores configuration set for refresh rates > 85hz. Why is that a good thing? I want to be able to run at 120hz for a hardware project I'm working on. I can patch the code for my own use, but this artificial limit seems wrong-headed, unless there's some issue with the Pi4 hardware that causes errors or other bad behavior > 85hz.

883a1a5

[6by9]

It's things like Kodi where running the display at 1080p100 and 1080p120 are valid if supported by the monitor, but just chew up rendering effort for zero gain.
You could say that Kodi should blacklist the higher refresh rates, but it's easier to do it at the platform level.

If you wanted to submit a PR to move that limit to a module parameter or an optional DT parameter of "raspberrypi,rpi-firmware-kms", then it would be considered.

[alanbork]

That seems like a reasonable compromise, but a little beyond my knowledge of how github works. For my needs I can just patch and recompile locally. But I know I'm not the only one asking for this feature, FYI.