[Bug 48652] [IVB CPU eDP] local flat panel stays blank, workaround: intel_iommu=igfx_off

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=48652

--- Comment #116 from Imre Deak <imre.deak at gmail.com> ---
(In reply to comment #115)
> Yes, it works.

Thanks, it narrows it down. I looked through the Intel HW IOMMU code and
haven't found anything obvious that could explain this.

OTOH, looking again at the dmesg with the crash
(dmesg-3.10.0-rc6-00406-g73bc88c) I can't see the HW IOMMU being enabled. I'd
expect "PCI-DMA: Intel(R) Virtualization Technology for Directed I/O". Instead
I see SWIOTLB being enabled there. But if you are using SWIOTLB I don't
understand why igfx_off makes any difference. Also the workaround in my patch
should be already active for SWIOTLB, so that shouldn't make any difference
either. Could you check if you had that workaround in your test kernel
(1625e7e549 - "drm/i915: make compact dma scatter lists creation work with
SWIOTLB backend")?

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