42 lines
1.6 KiB
Diff
42 lines
1.6 KiB
Diff
From: Jiri Kosina <jkosina@suse.cz>
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Date: Thu, 7 Aug 2014 16:29:53 +0200
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Subject: drm/i915: read HEAD register back in init_ring_common() to enforce
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ordering
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Origin: https://git.kernel.org/linus/ece4a17d237a79f63fbfaf3f724a12b6d500555c
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Withtout this, ring initialization fails reliabily during resume with
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[drm:init_ring_common] *ERROR* render ring initialization failed ctl 0001f001 head ffffff8804 tail 00000000 start 000e4000
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This is not a complete fix, but it is verified to make the ring
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initialization failures during resume much less likely.
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We were not able to root-cause this bug (likely HW-specific to Gen4 chips)
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yet. This is therefore used as a ducttape before problem is fully
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understood and proper fix created, so that people don't suffer from
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completely unusable systems in the meantime.
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The discussion and debugging is happening at
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https://bugs.freedesktop.org/show_bug.cgi?id=76554
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Signed-off-by: Jiri Kosina <jkosina@suse.cz>
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Cc: stable@vger.kernel.org
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Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
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---
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drivers/gpu/drm/i915/intel_ringbuffer.c | 3 +++
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1 file changed, 3 insertions(+)
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--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
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+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
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@@ -517,6 +517,9 @@ static int init_ring_common(struct intel
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else
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ring_setup_phys_status_page(ring);
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+ /* Enforce ordering by reading HEAD register back */
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+ I915_READ_HEAD(ring);
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+
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/* Initialize the ring. This must happen _after_ we've cleared the ring
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* registers with the above sequence (the readback of the HEAD registers
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* also enforces ordering), otherwise the hw might lose the new ring
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