Re: Forcing display size on Pi4

> On Dec 17, 2019, at 1:31 PM, Richard Miller <[email protected]> wrote:
> 
>> I have a 2K display that Plan9 forces to 1920x1080 resolution.
>> Poking around 9/bcm/screen.c indicates that setting vgasize=WxHxD
>> should force the size, but adding a suitable entry in cmdline.txt
>> just gives me a blank display.
>> 
>> Before I dig deeper, is this expected to work?
> 
> Possibly not.  I haven't tried vgasize= for years and there have been a
> lot of changes to the firmware & videocore mailbox interface since then.
> 
> Plan 9 should accept whatever resolution comes from the gpu, so it
> may be the firmware which "forces" 1920x1080.  Maybe gpu_mem needs
> to be bigger than the usual 16, or some other config.txt adjustment
> is needed?

I was able run earlier pis with a 4K@30Hz display but haven't tried this
with pi4. I had to use some custom parameters.

https://www.raspberrypi.org/documentation/configuration/hdmi-config.md

says to use hdmi_enable_4kp60=1 in config.txt if you have a 4k@60hz display.
You can choose custom modes as well. There is a config_hdmi_boost parameter
to increase HDMI drive strength but this doesn't work for pi4.

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