drm/i915/gvt: Fix drm_WARN issue where vgpu ptr is unavailable

When vgpu ptr is unavailable, the drm_WARN* can hang the whole system
due to the drm pointer is NULL. This patch fixes this issue by using
WARN directly which won't care about the drm pointer.

Fixes: 12d5861 ("drm/i915/gvt: Make WARN* drm specific where vgpu ptr is available")
Signed-off-by: Tina Zhang <tina.zhang@intel.com>
Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20200225053527.8336-1-tina.zhang@intel.com

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

@@ -392,7 +392,6 @@ static void handle_tlb_pending_event(struct intel_vgpu *vgpu, int ring_id)
 static void switch_mocs(struct intel_vgpu *pre, struct intel_vgpu *next,
 			int ring_id)
 {
-	struct drm_i915_private *i915 = pre->gvt->dev_priv;
 	struct drm_i915_private *dev_priv;
 	i915_reg_t offset, l3_offset;
 	u32 old_v, new_v;
@@ -407,7 +406,7 @@ static void switch_mocs(struct intel_vgpu *pre, struct intel_vgpu *next,
 	int i;
 
 	dev_priv = pre ? pre->gvt->dev_priv : next->gvt->dev_priv;
-	if (drm_WARN_ON(&i915->drm, ring_id >= ARRAY_SIZE(regs)))
+	if (drm_WARN_ON(&dev_priv->drm, ring_id >= ARRAY_SIZE(regs)))
 		return;
 
 	if (ring_id == RCS0 && IS_GEN(dev_priv, 9))
@@ -552,10 +551,9 @@ static void switch_mmio(struct intel_vgpu *pre,
 void intel_gvt_switch_mmio(struct intel_vgpu *pre,
 			   struct intel_vgpu *next, int ring_id)
 {
-	struct drm_i915_private *i915 = pre->gvt->dev_priv;
 	struct drm_i915_private *dev_priv;
 
-	if (drm_WARN_ON(&i915->drm, !pre && !next))
+	if (WARN(!pre && !next, "switch ring %d from host to HOST\n", ring_id))
 		return;
 
 	gvt_dbg_render("switch ring %d from %s to %s\n", ring_id,