[Intel-gfx] [PATCH] drm/i915: Suppress switch_mm emission between the same aliasing_ppgtt

[Joonas Lahtinen]

On ke, 2017-01-11 at 12:14 +0000, Chris Wilson wrote:
> When switching between contexts using the aliasing_ppgtt, the VM is
> shared. We don't need to reload the PD registers unless they are dirty.
> 
> Martin Peres reported an issue that looks like corruption between
> Haswell context switches, bisecting to commit f9326be5f1d3 ("drm/i915:
> Rearrange switch_context to load the aliasing ppgtt on first use").
> Switching between the same mm (the aliasing_ppgtt is used for all
> contexts in this case) should be a nop, but appears to trigger some
> side-effects in the context switch. However, as we know the switch
> is redundant in this case, we can skip it and continue to ignore the
> issue until somebody feels strong enough to investigate full-ppgtt on
> gen7 again!
> 
> Fixes: f9326be5f1d3 ("drm/i915: Rearrange switch_context to load the aliasing ppgtt on first use")
> Reported-by: Martin Peres <martin.peres at linux.intel.com>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Martin Peres <martin.peres at linux.intel.com>

Code looks good, could use the T-b's to verify.

Reviewed-by: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>

Regards, Joonas
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation