* Forcing display size on Pi4
@ 2019-12-17 21:05 Lyndon Nerenberg
2019-12-17 21:31 ` [9fans] " Richard Miller
0 siblings, 1 reply; 4+ messages in thread
From: Lyndon Nerenberg @ 2019-12-17 21:05 UTC (permalink / raw)
To: Plan 9 from Bell Labs
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? If it is I'll start
adding some kernel prints and try to find out what's not working.
--lyndon
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [9fans] Forcing display size on Pi4
2019-12-17 21:05 Forcing display size on Pi4 Lyndon Nerenberg
@ 2019-12-17 21:31 ` Richard Miller
2019-12-17 23:18 ` Bakul Shah
0 siblings, 1 reply; 4+ messages in thread
From: Richard Miller @ 2019-12-17 21:31 UTC (permalink / raw)
To: 9fans
> 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?
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [9fans] Forcing display size on Pi4
2019-12-17 21:31 ` [9fans] " Richard Miller
@ 2019-12-17 23:18 ` Bakul Shah
2019-12-18 0:13 ` hiro
0 siblings, 1 reply; 4+ messages in thread
From: Bakul Shah @ 2019-12-17 23:18 UTC (permalink / raw)
To: 9fans
> On Dec 17, 2019, at 1:31 PM, Richard Miller <9fans@hamnavoe.com> 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.
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2019-12-18 0:14 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2019-12-17 21:05 Forcing display size on Pi4 Lyndon Nerenberg
2019-12-17 21:31 ` [9fans] " Richard Miller
2019-12-17 23:18 ` Bakul Shah
2019-12-18 0:13 ` hiro
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