From: Oscar Mateo <oscar.ma...@intel.com>

If this comment is true for GEN6 and GEN7, I imagine it is for GEN8 as well:

    If we're in reset, we can assume the GPU is sufficiently idle to
    manually frob these bits. Ideally we could use the ring functions,
    except our error handling makes it quite difficult (can't use
    intel_ring_begin, ring->flush, or intel_ring_advance).

This exception was lost (wrongly, I suspect) in:

commit eeb9488e751a0a6401e7516a893efaf9d1f77fb5
Author: Ben Widawsky <b...@bwidawsk.net>
Date:   Fri Dec 6 14:11:10 2013 -0800

    drm/i915: Extract mm switching to function

    In order to do the full context switch with address space, it's
    convenient to have a way to switch the address space. We already have
    this in our code - just pull it out to be called by the context switch
    code later.

    v2: Rebased on BDW support. Required adding BDW.

Signed-off-by: Oscar Mateo <oscar.ma...@intel.com>
---
 drivers/gpu/drm/i915/i915_gem_gtt.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c 
b/drivers/gpu/drm/i915/i915_gem_gtt.c
index ad5c85b..49f103f 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -263,10 +263,23 @@ static int gen8_mm_sync_switch(struct i915_hw_ppgtt 
*ppgtt,
 static int gen8_mm_switch(struct i915_hw_ppgtt *ppgtt,
                          struct intel_engine_cs *ring)
 {
+       struct drm_device *dev = ppgtt->base.dev;
+       struct drm_i915_private *dev_priv = dev->dev_private;
+       int used_pd;
        int i, ret;
 
+       /* If we're in reset, we can assume the GPU is sufficiently idle to
+        * manually frob these bits. Ideally we could use the ring functions,
+        * except our error handling makes it quite difficult (can't use
+        * intel_ring_begin, ring->flush, or intel_ring_advance)
+        *
+        * FIXME: We should try not to special case reset
+        */
+       if (i915_reset_in_progress(&dev_priv->gpu_error))
+               return ppgtt->sync_switch_mm(ppgtt, ring);
+
        /* bit of a hack to find the actual last used pd */
-       int used_pd = ppgtt->num_pd_entries / GEN8_PDES_PER_PAGE;
+       used_pd = ppgtt->num_pd_entries / GEN8_PDES_PER_PAGE;
 
        for (i = used_pd - 1; i >= 0; i--) {
                dma_addr_t addr = ppgtt->pd_dma_addr[i];
-- 
1.9.0

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