linux-kernel - Re: more intel drm issues (was Re: [git pull] drm intel only fixes)

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Date:	Thu, 20 Jan 2011 12:44:24 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Chris Wilson <chris@...is-wilson.co.uk>
Cc:	Jeff Chua <jeff.chua.linux@...il.com>,
	Len Brown <len.brown@...el.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Dave Airlie <airlied@...ux.ie>, linux-kernel@...r.kernel.org,
	DRI mailing list <dri-devel@...ts.freedesktop.org>
Subject: Re: more intel drm issues (was Re: [git pull] drm intel only fixes)

On Thu, Jan 20, 2011 at 9:51 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> So how about just doing this in the loop? It will mean that the
> _first_ read uses the fast cached one (the common case, hopefully),
> but then if we loop, we'll use the slow exact one.
>
> (cut-and-paste, so whitespace isn't good):
>
>  diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c
> b/drivers/gpu/drm/i915/intel_ringbuffer.c
>  index 03e3370..11bbfb5 100644
>  --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
>  +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
>  @@ -961,6 +961,8 @@ int intel_wait_ring_buffer(struct
> intel_ring_buffer *ring, int n)
>                  msleep(1);
>                  if (atomic_read(&dev_priv->mm.wedged))
>                          return -EAGAIN;
>  +               /* Force a re-read. FIXME: what if read_status_page
> says 0 too */
>  +               ring->actual_head = 0;
>          } while (!time_after(jiffies, end));
>          trace_i915_ring_wait_end (dev);
>          return -EBUSY;

This makes no difference. And the reason is exactly that we get the
zero case that I had in the comment.

But THIS attached patch actually seems to fix the slow suspend for me.
I removed the accesses to "actual_head", because that whole field
seems to not be used.

So it seems like the intel_read_status_page() thing returns zero
forever when suspending. Maybe you can explain why.

                     Linus

View attachment "patch.diff" of type "text/x-patch" (1716 bytes)