[Bug 110780] RX 580 and 5K displays, bandwidth validation failed with multiple monitors

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=110780

            Bug ID: 110780
           Summary: RX 580 and 5K displays, bandwidth validation failed
                    with multiple monitors
           Product: DRI
           Version: unspecified
          Hardware: All
                OS: Linux (All)
            Status: NEW
          Severity: major
          Priority: medium
         Component: DRM/AMDgpu
          Assignee: dri-devel at lists.freedesktop.org
          Reporter: linuzel at gmail.com

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.

I tried a lot of kernel (includig drm-tip and 5.2-rc1) and they all have the
same issue.
My custom kernel with no validation is based on Ubuntu's 5.0.0-15-generic.

If I can help by providing more logs or test something ask and I will do my
best.

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