[Intel-gfx] drm/i915 4.5/4.6 stable backport request for CHV

[ville.syrjala at linux.intel.com]

From: Ville Syrjälä <ville.syrjala at linux.intel.com>

Several nasty i915 regressions affecting CHV slipped through
to 4.5 and 4.6.

The first fix we want in 4.5 and 4.6 is
commit caed361d83b2 ("drm/i915: Fix watermarks for VLV/CHV")
It won't cherry-pick cleanly to either one, so I've included conflict
free versions for both. This one fixes display FIFO underruns that can
lead to the screen totally blanking out.

The other one I'd like to have in 4.6 is
commit 9f6151c90390 ("drm/i915: Pass the correct crtc state to .update_plane()")
which avoids a totally corrupted display in some cases.

And the third on is a bit more annoying. The regression is caused by
commit 9dbaab56ac09 ("drm/i915: Exit cherryview_irq_handler() after one pass")
which I though we had prevented from getting out on its own, but turns
out I was wrong. It basically makes the GPU unusable, so we do need to
fix it somehow. The simple solution would be to revert it in 4.6 only.
The more complicated solution is to backport the proper fix, which more
or less requires the following set of commits [1], which is maybe a bit
too much for stable. I could try to trim it a bit perhaps, but then we
start to enter the territory of untested code which I don't particularly
like. Let me know what you think.

[1]
 1e1cace942ef ("drm/i915: Eliminate loop from VLV irq handler")
 a5e485a95c9c ("drm/i915: Clear VLV_IER around irq processing")
 4a0a0202b023 ("drm/i915: Clear VLV_MASTER_IER around irq processing")
 7ce4d1f2730f ("drm/i915: Clear VLV_IIR after PIPESTAT")
 34c7b8a7b8b5 ("drm/i915: Set up VLV_MASTER_IER consistently")
 e5328c43d46e ("drm/i915: Use GEN8_MASTER_IRQ_CONTROL consistently")
 71b8b41d5b35 ("drm/i915: Move DPINVGTT setup to vlv_display_irq_reset()")
 6b7eafc1b43d ("drm/i915: Warn if irq_mask isn't ~0 during vlv/cvh display irq postinstall")
 9ab981f22bef ("drm/i915: Use GEN5_IRQ_INIT() in vlv_display_irq_postinstall()")
 d6c698035892 ("drm/i915: Clear display interrupt before enabling when turning on the power well")
 8bb613068a63 ("drm/i915: Move vlv/chv display irq code to a more logical place")
 9918271efc7a ("drm/i915: Skip display irq setup if display irqs aren't flagged as enabled")
 ad22d10654ea ("drm/i915: Fix up vlv/chv display irq setup")
 93de68f94081 ("drm/i915: Remove "VLV magic" from irq setup")

Cc: stable at vger.kernel.org
-- 
Ville Syrjälä
Intel OTC