This is a note to let you know that I've just added the patch titled
drm/i915: read HEAD register back in init_ring_common() to enforce ordering
to the 3.16-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
drm-i915-read-head-register-back-in-init_ring_common-to-enforce-ordering.patch
and it can be found in the queue-3.16 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From ece4a17d237a79f63fbfaf3f724a12b6d500555c Mon Sep 17 00:00:00 2001
From: Jiri Kosina <jkosina@xxxxxxx>
Date: Thu, 7 Aug 2014 16:29:53 +0200
Subject: drm/i915: read HEAD register back in init_ring_common() to enforce ordering
From: Jiri Kosina <jkosina@xxxxxxx>
commit ece4a17d237a79f63fbfaf3f724a12b6d500555c upstream.
Withtout this, ring initialization fails reliabily during resume with
[drm:init_ring_common] *ERROR* render ring initialization failed ctl 0001f001 head ffffff8804 tail 00000000 start 000e4000
This is not a complete fix, but it is verified to make the ring
initialization failures during resume much less likely.
We were not able to root-cause this bug (likely HW-specific to Gen4 chips)
yet. This is therefore used as a ducttape before problem is fully
understood and proper fix created, so that people don't suffer from
completely unusable systems in the meantime.
The discussion and debugging is happening at
https://bugs.freedesktop.org/show_bug.cgi?id=76554
Signed-off-by: Jiri Kosina <jkosina@xxxxxxx>
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/i915/intel_ringbuffer.c | 3 +++
1 file changed, 3 insertions(+)
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -517,6 +517,9 @@ static int init_ring_common(struct intel
else
ring_setup_phys_status_page(ring);
+ /* Enforce ordering by reading HEAD register back */
+ I915_READ_HEAD(ring);
+
/* Initialize the ring. This must happen _after_ we've cleared the ring
* registers with the above sequence (the readback of the HEAD registers
* also enforces ordering), otherwise the hw might lose the new ring
Patches currently in stable-queue which might be from jkosina@xxxxxxx are
queue-3.16/drm-i915-read-head-register-back-in-init_ring_common-to-enforce-ordering.patch
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