drm/i915: Track ggtt fence reservations under its own mutex

We can reduce the locking for fence registers from the dev->struct_mutex
to a local mutex. We could introduce a mutex for the sole purpose of
tracking the fence acquisition, except there is a little bit of overlap
with the fault tracking, so use the i915_ggtt.mutex as it covers both.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190822060914.2671-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gvt/aperture_gm.c

@@ -172,14 +172,14 @@ static void free_vgpu_fence(struct intel_vgpu *vgpu)
 
 	intel_runtime_pm_get(&dev_priv->runtime_pm);
 
-	mutex_lock(&dev_priv->drm.struct_mutex);
+	mutex_lock(&dev_priv->ggtt.vm.mutex);
 	_clear_vgpu_fence(vgpu);
 	for (i = 0; i < vgpu_fence_sz(vgpu); i++) {
 		reg = vgpu->fence.regs[i];
 		i915_unreserve_fence(reg);
 		vgpu->fence.regs[i] = NULL;
 	}
-	mutex_unlock(&dev_priv->drm.struct_mutex);
+	mutex_unlock(&dev_priv->ggtt.vm.mutex);
 
 	intel_runtime_pm_put_unchecked(&dev_priv->runtime_pm);
 }
@@ -195,7 +195,7 @@ static int alloc_vgpu_fence(struct intel_vgpu *vgpu)
 	intel_runtime_pm_get(rpm);
 
 	/* Request fences from host */
-	mutex_lock(&dev_priv->drm.struct_mutex);
+	mutex_lock(&dev_priv->ggtt.vm.mutex);
 
 	for (i = 0; i < vgpu_fence_sz(vgpu); i++) {
 		reg = i915_reserve_fence(dev_priv);
@@ -207,7 +207,7 @@ static int alloc_vgpu_fence(struct intel_vgpu *vgpu)
 
 	_clear_vgpu_fence(vgpu);
 
-	mutex_unlock(&dev_priv->drm.struct_mutex);
+	mutex_unlock(&dev_priv->ggtt.vm.mutex);
 	intel_runtime_pm_put_unchecked(rpm);
 	return 0;
 out_free_fence:
@@ -220,7 +220,7 @@ out_free_fence:
 		i915_unreserve_fence(reg);
 		vgpu->fence.regs[i] = NULL;
 	}
-	mutex_unlock(&dev_priv->drm.struct_mutex);
+	mutex_unlock(&dev_priv->ggtt.vm.mutex);
 	intel_runtime_pm_put_unchecked(rpm);
 	return -ENOSPC;
 }