@@ -2529,7 +2529,6 @@ static void i965_write_fence_reg(struct drm_device *dev, int reg,
drm_i915_private_t *dev_priv = dev->dev_private;
int fence_reg;
int fence_pitch_shift;
- uint64_t val;
if (INTEL_INFO(dev)->gen >= 6) {
fence_reg = FENCE_REG_SANDYBRIDGE_0;
@@ -2539,8 +2538,23 @@ static void i965_write_fence_reg(struct drm_device *dev, int reg,
fence_pitch_shift = I965_FENCE_PITCH_SHIFT;
}
+ fence_reg += reg * 8;
+
+ /* To w/a incoherency with non-atomic 64-bit register updates,
+ * we split the 64-bit update into two 32-bit writes. In order
+ * for a partial fence not to be evaluated between writes, we
+ * precede the update with write to turn off the fence register,
+ * and only enable the fence as the last step.
+ *
+ * For extra levels of paranoia, we make sure each step lands
+ * before applying the next step.
+ */
+ I915_WRITE(fence_reg, 0);
+ POSTING_READ(fence_reg);
+
if (obj) {
u32 size = obj->gtt_space->size;
+ uint64_t val;
val = (uint64_t)((obj->gtt_offset + size - 4096) &
0xfffff000) << 32;
@@ -2549,12 +2563,16 @@ static void i965_write_fence_reg(struct drm_device *dev, int reg,
if (obj->tiling_mode == I915_TILING_Y)
val |= 1 << I965_FENCE_TILING_Y_SHIFT;
val |= I965_FENCE_REG_VALID;
- } else
- val = 0;
- fence_reg += reg * 8;
- I915_WRITE64(fence_reg, val);
- POSTING_READ(fence_reg);
+ I915_WRITE(fence_reg + 4, val >> 32);
+ POSTING_READ(fence_reg + 4);
+
+ I915_WRITE(fence_reg + 0, val);
+ POSTING_READ(fence_reg);
+ } else {
+ I915_WRITE(fence_reg + 4, 0);
+ POSTING_READ(fence_reg + 4);
+ }
}
static void i915_write_fence_reg(struct drm_device *dev, int reg,
This is a note to let you know that I have just added a patch titled drm/i915: Fix incoherence with fence updates on Sandybridge+ to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree which can be found at: http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue This patch is scheduled to be released in version 3.8.13.6. If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.8.y.z tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Kamal ------ From 667cf8f8c8d11e3405ad04fc996887df6149b275 Mon Sep 17 00:00:00 2001 From: Chris Wilson <chris@chris-wilson.co.uk> Date: Wed, 10 Jul 2013 13:36:23 +0100 Subject: drm/i915: Fix incoherence with fence updates on Sandybridge+ commit d18b9619034230b6f945e215276425636ca401fe upstream. This hopefully fixes the root cause behind the workaround added in commit 25ff1195f8a0b3724541ae7bbe331b4296de9c06 Author: Chris Wilson <chris@chris-wilson.co.uk> Date: Thu Apr 4 21:31:03 2013 +0100 drm/i915: Workaround incoherence between fences and LLC across multiple CPUs Thanks to further investigation by Jon Bloomfield, he realised that the 64-bit register might be broken up by the hardware into two 32-bit writes (a problem we have encountered elsewhere). This non-atomicity would then cause an issue where a second thread would see an intermediate register state (new high dword, old low dword), and this register would randomly be used in preference to its own thread register. This would cause the second thread to read from and write into a fairly random tiled location. Breaking the operation into 3 explicit 32-bit updates (first disable the fence, poke the upper bits, then poke the lower bits and enable) ensures that, given proper serialisation between the 32-bit register write and the memory transfer, that the fence value is always consistent. Armed with this knowledge, we can explain how the previous workaround work. The key to the corruption is that a second thread sees an erroneous fence register that conflicts and overrides its own. By serialising the fence update across all CPUs, we have a small window where no GTT access is occurring and so hide the potential corruption. This also leads to the conclusion that the earlier workaround was incomplete. v2: Be overly paranoid about the order in which fence updates become visible to the GPU to make really sure that we turn the fence off before doing the update, and then only switch the fence on afterwards. Signed-off-by: Jon Bloomfield <jon.bloomfield@intel.com> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Carsten Emde <C.Emde@osadl.org> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> Signed-off-by: Kamal Mostafa <kamal@canonical.com> --- drivers/gpu/drm/i915/i915_gem.c | 30 ++++++++++++++++++++++++------ 1 file changed, 24 insertions(+), 6 deletions(-) -- 1.8.1.2