For reasons unknown Sandybridge GT1 (at least) will eventually hang when it encounters a ring wraparound at offset 0. The test case that reproduces the bug reliably forces a large number of interrupted context switches, thereby causing very frequent ring wraparounds, but there are similar bug reports in the wild with the same symptoms, seqno writes stop just before the wrap and the ringbuffer at address 0. It is also timing crucial, but adding various delays hasn't helped pinpoint where the window lies.
Whether the fault is restricted to the ringbuffer itself or the GTT addressing is unclear, but moving the ringbuffer fixes all the hangs I have been able to reproduce. References: (e.g.) https://bugs.freedesktop.org/show_bug.cgi?id=93262 Testcase: igt/gem_exec_whisper/render-contexts-interruptible #snb-gt1 Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk> Cc: sta...@vger.kernel.org --- drivers/gpu/drm/i915/intel_ringbuffer.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c index 6b4952031e30..2f13ab2a1098 100644 --- a/drivers/gpu/drm/i915/intel_ringbuffer.c +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c @@ -2113,10 +2113,12 @@ int intel_pin_and_map_ringbuffer_obj(struct drm_device *dev, struct drm_i915_private *dev_priv = to_i915(dev); struct i915_ggtt *ggtt = &dev_priv->ggtt; struct drm_i915_gem_object *obj = ringbuf->obj; + /* Ring wraparound at offset 0 sometimes hangs. No idea why. */ + unsigned flags = PIN_OFFSET_BIAS | 4096; int ret; if (HAS_LLC(dev_priv) && !obj->stolen) { - ret = i915_gem_obj_ggtt_pin(obj, PAGE_SIZE, 0); + ret = i915_gem_obj_ggtt_pin(obj, PAGE_SIZE, flags); if (ret) return ret; @@ -2132,7 +2134,8 @@ int intel_pin_and_map_ringbuffer_obj(struct drm_device *dev, return -ENOMEM; } } else { - ret = i915_gem_obj_ggtt_pin(obj, PAGE_SIZE, PIN_MAPPABLE); + ret = i915_gem_obj_ggtt_pin(obj, PAGE_SIZE, + flags | PIN_MAPPABLE); if (ret) return ret; -- 2.8.0.rc3 _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx
