[Intel-gfx] [PATCH 2/2] [v2] drm/i915: Disable GGTT PTEs on GEN6+ suspend

[Chris Wilson]

On Wed, Oct 16, 2013 at 09:21:30AM -0700, Ben Widawsky wrote:
> Once the machine gets to a certain point in the suspend process, we
> expect the GPU to be idle. If it is not, we might corrupt memory.
> Empirically (with an early version of this patch) we have seen this is
> not the case. We cannot currently explain why the latent GPU writes
> occur.
> 
> In the technical sense, this patch is a workaround in that we have an
> issue we can't explain, and the patch indirectly solves the issue.
> However, it's really better than a workaround because we understand why
> it works, and it really should be a safe thing to do in all cases.
> 
> The noticeable effect other than the debug messages would be an increase
> in the suspend time. I have not measure how expensive it actually is.
> 
> I think it would be good to spend further time to root cause why we're
> seeing these latent writes, but it shouldn't preclude preventing the
> fallout.
> 
> NOTE: It should be safe (and makes some sense IMO) to also keep the
> VALID bit unset on resume when we clear_range(). I've opted not to do
> this as properly clearing those bits at some later point would be extra
> work.
> 
> v2: Fix bugzilla link

And the other one?

> Bugzilla: http://bugs.freedesktop.org/6549://bugs.freedesktop.org/show_bug.cgi?id=65496
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=59321
> Tested-by: Takashi Iwai <tiwai at suse.de>
> Tested-by: Paulo Zanoni <paulo.r.zanoni at intel.com>
> Signed-off-by: Ben Widawsky <ben at bwidawsk.net>

So clearing the valid bit should result in the GPU reporting errors for
delayed accesses, but none were reported?
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre