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

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Message-ID: <20140708085901.GI26405@nuc-i3427.alporthouse.com>
Date:	Tue, 8 Jul 2014 09:59:01 +0100
From:	Chris Wilson <chris@...is-wilson.co.uk>
To:	Jiri Kosina <jkosina@...e.cz>
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 Tue, Jul 08, 2014 at 12:15:31AM +0200, Jiri Kosina wrote:
> 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.

Are you using the extra patches on bug 76554? If not, try

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index e18ed05dc0d5..48326f9628d4 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -526,6 +526,9 @@ static int init_ring_common(struct intel_engine_cs *ring)
                        ((ringbuf->size - PAGE_SIZE) & RING_NR_PAGES)
                        | RING_VALID);
 
+       I915_WRITE_HEAD(ring, 0);
+       (void)I915_READ_HEAD(ring);
+
        /* If the head is still not zero, the ring is dead */
        if (wait_for((I915_READ_CTL(ring) & RING_VALID) != 0 &&
                     I915_READ_START(ring) == i915_gem_obj_ggtt_offset(obj) &&

-- 
Chris Wilson, Intel Open Source Technology Centre
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