Re: [Mesa-dev] [PATCH 1/2] i965: Make intel_emit_linear_blit handle Gen8+ alignment restrictions.

From: Kenneth Graunke <kenneth@whitecape.org>
To: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Intel Graphics Development <intel-gfx@lists.freedesktop.org>
Subject: Re: [Mesa-dev] [PATCH 1/2] i965: Make intel_emit_linear_blit handle Gen8+ alignment restrictions.
Date: Wed, 06 May 2015 10:41:34 -0700	[thread overview]
Message-ID: <30445906.Uy24vLNqI1@eiger> (raw)
In-Reply-To: <877fslzkhj.fsf@gaia.fi.intel.com>

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On Wednesday, May 06, 2015 08:25:28 PM Mika Kuoppala wrote:
> Chris Wilson <chris@chris-wilson.co.uk> writes:
> 
> > On Wed, May 06, 2015 at 03:38:44PM +0200, Daniel Vetter wrote:
> >> On Tue, Apr 21, 2015 at 10:13:31PM -0700, Kenneth Graunke wrote:
> >> > The BLT engine on Gen8+ requires linear surfaces to be cacheline
> >> > aligned.  This restriction was added as part of converting the BLT to
> >> > use 48-bit addressing.
> >> > 
> >> > intel_emit_linear_blit needs to handle blits that are not cacheline
> >> > aligned, as we use it for arbitrary glBufferSubData calls and subrange
> >> > mappings.
> >> > 
> >> > Since intel_emit_linear_blit uses 1 byte per pixel, we can use the src/dst
> >> > pixel X offset field to represent the unaligned portion, and subtract
> >> > that from the address so it's cacheline aligned.
> >> > 
> >> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=88521
> >> > Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
> >> > Cc: mesa-stable@lists.freedesktop.org
> >> 
> >> s/cacheline/page/ afaik, and nope it's not documented. Chris&Mika learned
> >> that the hard way. Adding them to correct me in case I make a mess again.
> >
> > It's cacheline.
> >
> > Issue: if the 1st pixel in XY_SRC_COPY  is not CL aligned when SRC or
> > DST are linear that will cause failure.
> >
> > https://vthsd.fm.intel.com/hsd/bdwgfx/bug_de/default.aspx?bug_de_id=1912704
> > -Chris
> >
> 
> FWIF, I ended up doing it like this in igt:
> 
> http://lists.freedesktop.org/archives/intel-gfx/2015-January/059191.html
> 
> And I think the documentation was updated on the restrictions.
> 
> -Mika

Yeah, I saw the updated documentation, remembered that Chris warned me
about this a while back (I think I just said "ugh" and promptly forgot
about it), and finally fixed Mesa.  It's all upstream and working now.

Huge thanks for tracking this down and getting it documented!

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