Comment 68 for bug 727594

(In reply to comment #13)
> (In reply to comment #11)
> > BTW, while a suspend-resume should reset the gpu, I see this:
> >
> > [31055.564022] [drm] Manually setting wedged to 0
> > [31055.564022] [drm:i915_reset] *ERROR* Failed to reset chip.
> > Why does it fail?
>
> It fails because we have not found the means to successfully reset that chipset
> yet. It may well be the only way is to power cycle the PCI device. Meh.
>
> > The units are not busy anymore according to intel_gpu_top, so I'd expect "echo
> > 0 > /sys/kernel/debug/dri/0/i915_wedged" should unwedge it, but it doesn't
>
> The units are idle because the chip hit a fatal error and disabled those units.

I don't think so. They are only idle after coming back out of suspend to ram, so I think it's probably because the GPU was power-cycled.
Both resume from disk and resume from ram have the same effect here.
I think it would be very helpful if KMS/DRM could recover from the GPU hang after suspend to ram or suspend to disk, when the GPU was power-cycled. It used to be the case that 'echo 1 > i915_wedged' would restart the driver after resume, but it seems some internals have changed so that this no longer works. If it would be able to recover in this case it would avoid the need to completely reboot the system to recover.