Commit 2e7c2083 authored by Jiri Kosina's avatar Jiri Kosina Committed by Greg Kroah-Hartman

drm/i915: read HEAD register back in init_ring_common() to enforce ordering

commit ece4a17d 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=76554Signed-off-by: default avatarJiri Kosina <jkosina@suse.cz>
Signed-off-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 1fee660a
...@@ -517,6 +517,9 @@ static int init_ring_common(struct intel_engine_cs *ring) ...@@ -517,6 +517,9 @@ static int init_ring_common(struct intel_engine_cs *ring)
else else
ring_setup_phys_status_page(ring); 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 /* Initialize the ring. This must happen _after_ we've cleared the ring
* registers with the above sequence (the readback of the HEAD registers * registers with the above sequence (the readback of the HEAD registers
* also enforces ordering), otherwise the hw might lose the new ring * also enforces ordering), otherwise the hw might lose the new ring
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment