From d7ab5cc9631c29eb58da4ab803d62344220cf8b8 Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Wed, 1 Feb 2012 18:25:28 +0000 Subject: [PATCH 1/2] drm/i915: Remove use of the autoreported ringbuffer HEAD position This is a revert of 6aa56062eaba67adfb247cded244fd877329588d. This was originally introduced to workaround reads of the ringbuffer registers returning 0 on SandyBridge causing hangs due to ringbuffer overflow. The root cause here was reads through the GT powerwell require the forcewake dance, something we only learnt of later. Now it appears that reading the reported head position from the HWS is returning garbage, leading once again to hangs. For example, on q35 the autoreported head reports: [ 217.975608] head now 00010000, actual 00010000 [ 436.725613] head now 00200000, actual 00200000 [ 462.956033] head now 00210000, actual 00210010 [ 485.501409] head now 00400000, actual 00400020 [ 508.064280] head now 00410000, actual 00410000 [ 530.576078] head now 00600000, actual 00600020 [ 553.273489] head now 00610000, actual 00610018 which appears reasonably sane. In contrast, if we look at snb: [ 141.970680] head now 00e10000, actual 00008238 [ 141.974062] head now 02734000, actual 000083c8 [ 141.974425] head now 00e10000, actual 00008488 [ 141.980374] head now 032b5000, actual 000088b8 [ 141.980885] head now 03271000, actual 00008950 [ 142.040628] head now 02101000, actual 00008b40 [ 142.180173] head now 02734000, actual 00009050 [ 142.181090] head now 00000000, actual 00000ae0 [ 142.183737] head now 02734000, actual 00009050 In addition, the automatic reporting of the head position is scheduled to be defeatured in the future. It has no more utility, remove it. Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=45492 Signed-off-by: Chris Wilson --- drivers/gpu/drm/i915/intel_ringbuffer.c | 14 +------------- 1 files changed, 1 insertions(+), 13 deletions(-) diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c index 023739f..620b2ed 100644 --- a/drivers/gpu/drm/i915/intel_ringbuffer.c +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c @@ -287,7 +287,7 @@ static int init_ring_common(struct intel_ring_buffer *ring) I915_WRITE_CTL(ring, ((ring->size - PAGE_SIZE) & RING_NR_PAGES) - | RING_REPORT_64K | RING_VALID); + | RING_VALID); /* If the head is still not zero, the ring is dead */ if ((I915_READ_CTL(ring) & RING_VALID) == 0 || @@ -1059,18 +1059,6 @@ int intel_wait_ring_buffer(struct intel_ring_buffer *ring, int n) struct drm_device *dev = ring->dev; struct drm_i915_private *dev_priv = dev->dev_private; unsigned long end; - u32 head; - - /* If the reported head position has wrapped or hasn't advanced, - * fallback to the slow and accurate path. - */ - head = intel_read_status_page(ring, 4); - if (head > ring->head) { - ring->head = head; - ring->space = ring_space(ring); - if (ring->space >= n) - return 0; - } trace_i915_ring_wait_begin(ring); if (drm_core_check_feature(dev, DRIVER_GEM)) -- 1.7.9