Re: [PATCH v2 0/2] drm/i915/bxt: work around HW coherency issue

From: Imre Deak <imre.deak@intel.com>
To: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula@intel.com>,
	intel-gfx@lists.freedesktop.org,
	Mika Kuoppala <mika.kuoppala@intel.com>
Subject: Re: [PATCH v2 0/2] drm/i915/bxt: work around HW coherency issue
Date: Fri, 14 Aug 2015 16:26:29 +0300	[thread overview]
Message-ID: <1439558789.31146.8.camel@intel.com> (raw)
In-Reply-To: <20150814124958.GB27217@nuc-i3427.alporthouse.com>

On pe, 2015-08-14 at 13:49 +0100, Chris Wilson wrote:
> On Fri, Aug 14, 2015 at 03:38:55PM +0300, Imre Deak wrote:
> > This is a v2 of [1]. Since v1 the HW team confirmed that there is an
> > HW issue in A steppings with the GPU/CPU snoop logic, which explains why
> > we need this workaround.
> 
> I've been testing this extensively, and I do believe we can use clflush
> for all gen - it is a measurable improvement over using the
> heavyweight/locked read of ACTHD, and none of the coherency tests have
> thrown any warnings (over a period of a couple of months now).

Ok. Do you mean only places where there is already the ACTHD w/a, or to
extend it also to other platforms?

Imo doing this as a follow-up to this patchset would make sense, to keep
platform specific changes separate.

--Imre

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