linux-kernel - Re: [Intel-gfx] Linux 3.16-rc2

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Date:	Tue, 8 Jul 2014 00:15:31 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Chris Wilson <chris@...is-wilson.co.uk>
cc:	Thomas Meyer <thomas@...3r.de>,
	"intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Pavel Machek <pavel@....cz>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [Intel-gfx] Linux 3.16-rc2

On Mon, 7 Jul 2014, Chris Wilson wrote:

> > > this patch on top of v3.16-rc3-62-gd92a333 makes the resume from ram
> > > regression go away on my machine:
> > 
> > Hm, we could conditionalize this hack on IS_G4X ... Chris, thoughts?
> 
> As different machines favour different w/a, I think the issue is mostly
> timing related. It could be sequence of register writes, but we tried
> different orders early on. The next experiment I guess would be to
> insert small delays between each write to see if that helps. Or to write
> each register twice.

I actually tried to introduce rather large delays between individual 
I915_WRITE() calls in the ring initialization sequence a couple weeks ago 
already, but it resulted in complete machine lockup (which is worse than 
my usual symptoms) during resume. Therefore I probably lack the knowledge 
of internal workings of the HW that would allow me to guess what the 
reasonable timeout value should be.

Willing to test any patches.

-- 
Jiri Kosina
SUSE Labs
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