[Bug 94605] [SKL] Flashing black screen ([drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe A FIFO underrun)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=94605

--- Comment #86 from Mauro Santos <registo.mailling at gmail.com> ---
(In reply to syphyr from comment #85)
> [    0.076183] DMAR: Host address width 39
> [    0.076184] DMAR: DRHD base: 0x000000fed90000 flags: 0x0
> [    0.076188] DMAR: dmar0: reg_base_addr fed90000 ver 1:0 cap
> 1c0000c40660462 ecap 7e3ff0505e
> [    0.076189] DMAR: DRHD base: 0x000000fed91000 flags: 0x1
> [    0.076193] DMAR: dmar1: reg_base_addr fed91000 ver 1:0 cap
> d2008c40660462 ecap f050da
> [    0.076194] DMAR: RMRR base: 0x0000008aca9000 end: 0x0000008acc8fff
> [    0.076194] DMAR: RMRR base: 0x0000008b800000 end: 0x0000008fffffff
> [    0.076196] DMAR-IR: IOAPIC id 2 under DRHD base  0xfed91000 IOMMU 1
> [    0.076197] DMAR-IR: HPET id 0 under DRHD base 0xfed91000
> [    0.076198] DMAR-IR: x2apic is disabled because BIOS sets x2apic opt out
> bit.
> [    0.076198] DMAR-IR: Use 'intremap=no_x2apic_optout' to override the BIOS
> setting.
> [    0.077630] DMAR-IR: Enabled IRQ remapping in xapic mode

As far as I know, if you don't see "kernel: DMAR: IOMMU enabled" the iommu is
not being used, despite you seeing the confirmation "kernel: DMAR: Disable GFX
device mapping" that the igfx_off option as been accepted.

I might be wrong though, if someone else could chime in and confirm how it
works it would be great.

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