[Bug 92485] [sna ivb] screen corruption (Bisected)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=92485

--- Comment #3 from Chris Wilson <chris at chris-wilson.co.uk> ---
That's cacheline dirt. I suspect it from mesa rendering into the buffer
overriding the PTE settings that say it must be rendered uncached. There are
also a couple of kernel bugs where the GPU writes are not being flushed before
the pageflip.

For mesa try:

diff --git a/src/mesa/drivers/dri/i965/brw_defines.h
b/src/mesa/drivers/dri/i965/brw_defines.h
index 393f17a..164d54b 100644
--- a/src/mesa/drivers/dri/i965/brw_defines.h
+++ b/src/mesa/drivers/dri/i965/brw_defines.h
@@ -2709,13 +2709,13 @@ enum brw_wm_barycentric_interp_mode {
  * On Ivybridge, the PTEs do have a cache-in-L3 bit, so setting MOCS to 0
  * may still respect that.
  */
-#define GEN7_MOCS_L3                    1
+#define GEN7_MOCS_L3                    0

 /* Ivybridge only: cache in LLC.
  * Specifying zero here means to use the PTE values set by the kernel;
  * non-zero overrides the PTE values.
  */
-#define IVB_MOCS_LLC                    (1 << 1)
+#define IVB_MOCS_LLC                    0

 /* Baytrail only: snoop in CPU cache */
 #define BYT_MOCS_SNOOP                  (1 << 1)


For the kernel you need:

diff --git a/drivers/gpu/drm/i915/intel_display.c
b/drivers/gpu/drm/i915/intel_display.c
index 107c6c0519fd..42d91d6adf9b 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -11233,6 +11233,12 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
        work->gtt_offset = intel_plane_obj_offset(to_intel_plane(primary), obj)
                                                  + intel_crtc->dspaddr_offset;

+       if (obj->last_write_req) {
+               ret = i915_gem_check_olr(obj->last_write_req);
+               if (ret)
+                       goto cleanup_unpin;
+       }
+
        if (mmio_flip) {
                ret = intel_queue_mmio_flip(dev, crtc, fb, obj, ring,
                                            page_flip_flags);
@@ -11242,12 +11248,6 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
                i915_gem_request_assign(&work->flip_queued_req,
                                        obj->last_write_req);
        } else {
-               if (obj->last_write_req) {
-                       ret = i915_gem_check_olr(obj->last_write_req);
-                       if (ret)
-                               goto cleanup_unpin;
-               }
-
                ret = dev_priv->display.queue_flip(dev, crtc, fb, obj, ring,
                                                   page_flip_flags);
                if (ret)

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