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

From: Chris Wilson <chris@chris-wilson.co.uk>
To: Imre Deak <imre.deak@intel.com>
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 14:31:20 +0100	[thread overview]
Message-ID: <20150814133120.GF27217@nuc-i3427.alporthouse.com> (raw)
In-Reply-To: <1439558789.31146.8.camel@intel.com>

On Fri, Aug 14, 2015 at 04:26:29PM +0300, Imre Deak wrote:
> 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?

I mean replace the current ACTHD w/a.

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

Agreed. Get the w/a in place, then do the conversion so that we have a
safe fallback.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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