RX 580 and 5K displays, bandwidth validation failed whith multiple monitors

[Harry Wentland]

On 2019-05-27 10:58 a.m., Gaël HERMET wrote:
> Hi,
> 
> I have been facing an issue with my 5K display (iiyama ProLite
> XB2779QQS-S1).
> 
> It works fine as long as it is the only active monitor, as soon as I
> activate another monitor the main one (5k) can't display more than 4k.
> 
> Debug using "echo 0x4 > /sys/module/drm/parameters/debug" show this :
> mai 23 09:01:22 bureau-gael /usr/lib/gdm3/gdm-x-session[3465]: (EE)
> AMDGPU(0): failed to set mode: Invalid argument
> mai 23 09:01:22 bureau-gael kernel: [drm:dce112_validate_bandwidth
> [amdgpu]] dce112_validate_bandwidth: Bandwidth validation failed!
> 
> I disabled the check by forcing is_display_configuration_supported to
> return true in dce_calcs.c and it works fine.
> 
> Anything I can do to correct this bandwidth calculation ?
> 

The bandwidth formulas come from our HW teams and usually leave a good
margin of error. Changing the formulas to allow for your case isn't a
correction as it might cause issues in certain scenarious, i.e. there's
no more guarantee that things work as expected.

Examples are 4k video playback (especially multiple videos), gaming.
Anything that does a lot of GPU memory access.

Issues that might appear are underflow, i.e. white lines on the screen.
In extreme cases underflow might even hang the entire display pipe.

Harry

> 
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