4.5-stable review patch. If anyone has any objections, please let me know. ------------------ From: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> commit 1b3e885a05d4f0a35dde035724e7c6453d2cbe71 upstream. 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 <chris@xxxxxxxxxxxxxxxxxx> Acked-by: Daniel Vetter <daniel.vetter@xxxxxxxx> Link: http://patchwork.freedesktop.org/patch/msgid/1460565315-7748-12-git-send-email-chris@xxxxxxxxxxxxxxxxxx (cherry picked from commit a687a43a48f0f91ba37dce5a14b467258ed6f035) Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/gpu/drm/i915/intel_ringbuffer.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) --- a/drivers/gpu/drm/i915/intel_ringbuffer.c +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c @@ -2031,10 +2031,12 @@ int intel_pin_and_map_ringbuffer_obj(str { struct drm_i915_private *dev_priv = to_i915(dev); 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; @@ -2050,7 +2052,8 @@ int intel_pin_and_map_ringbuffer_obj(str 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; -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html