[Bug 101499] Black screen when detaching HDMI cable (AMD A10-9620P)

[bugzilla-daemon@freedesktop.org]

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https://bugs.freedesktop.org/show_bug.cgi?id=101499

--- Comment #11 from Michel Dänzer <michel@daenzer.net> ---
(In reply to Carlo Caione from comment #10)
> Probably I'm missing something, but when the HDMI is connected everything
> works fine, with the scanout buffer correctly displayed on the laptop panel
> + external monitor. The problem starts when we _disconnect_ the HDMI cable.

At least some of the errors you referenced in comment 8 already happen before
that. They're related to failed attempts at page flipping. xf86-video-amdgpu
manages to chug along regardless.

When you unplug the HDMI cable is presumably when

> Jun 19 17:10:31 endless gdm-Xorg-:0[672]: (EE) AMDGPU(0): failed to set mode: Invalid argument

appears, i.e. drmModeSetCrtc() fails, presumably (not 100% sure about this part
though) because the new, smaller scanout buffer cannot fit into VRAM while the
old, larger one is still being scanned out.

> Also if it was a problem with VRAM being too small, why toggling the DPMS
> makes the laptop panel working fine again?

Toggling DPMS off disables scanout, which allows the old scanout buffer to be
moved out of VRAM, so the new one can be moved in.


Some details might differ from the above, but that should be roughly what's
happening.

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