[Bug 109477] [regression, bisected] [i915] setting initial watermarks on gen 7 IVYBRIDGE causes blank lines on monitor

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=109477

--- Comment #17 from Ville Syrjala <ville.syrjala at linux.intel.com> ---
This thing is super mysterious.

Please grab
intel_reg read 0x70080 0x71080 0x72080 0x70280 0x71280 0x72280
intel_reg dump
intel_watermark

before and after 
3e869fd34856 ("Revert "drm/i915/fbdev: Actually configure untiled displays"")

I see DMAR is also active. Try booting with 'intel_iommu=igfx_off' passed to
the kernel cmdline to see if that has any effect.

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