1 files changed, 41 insertions, 10 deletions

diff --git a/drivers/gpu/drm/i915/display/intel_vblank.c b/drivers/gpu/drm/i915/display/intel_vblank.c
index 2cec2abf9746..fe256bf7b485 100644
--- a/drivers/gpu/drm/i915/display/intel_vblank.c
+++ b/drivers/gpu/drm/i915/display/intel_vblank.c
@@ -265,6 +265,32 @@ int intel_crtc_scanline_to_hw(struct intel_crtc *crtc, int scanline)
 	return (scanline + vtotal - crtc->scanline_offset) % vtotal;
 }
 
+/*
+ * The uncore version of the spin lock functions is used to decide
+ * whether we need to lock the uncore lock or not.  This is only
+ * needed in i915, not in Xe.
+ *
+ * This lock in i915 is needed because some old platforms (at least
+ * IVB and possibly HSW as well), which are not supported in Xe, need
+ * all register accesses to the same cacheline to be serialized,
+ * otherwise they may hang.
+ */
+static void intel_vblank_section_enter(struct drm_i915_private *i915)
+	__acquires(i915->uncore.lock)
+{
+#ifdef I915
+	spin_lock(&i915->uncore.lock);
+#endif
+}
+
+static void intel_vblank_section_exit(struct drm_i915_private *i915)
+	__releases(i915->uncore.lock)
+{
+#ifdef I915
+	spin_unlock(&i915->uncore.lock);
+#endif
+}
+
 static bool i915_get_crtc_scanoutpos(struct drm_crtc *_crtc,
 				     bool in_vblank_irq,
 				     int *vpos, int *hpos,
@@ -302,11 +328,12 @@ static bool i915_get_crtc_scanoutpos(struct drm_crtc *_crtc,
 	}
 
 	/*
-	 * Lock uncore.lock, as we will do multiple timing critical raw
-	 * register reads, potentially with preemption disabled, so the
-	 * following code must not block on uncore.lock.
+	 * Enter vblank critical section, as we will do multiple
+	 * timing critical raw register reads, potentially with
+	 * preemption disabled, so the following code must not block.
 	 */
-	spin_lock_irqsave(&dev_priv->uncore.lock, irqflags);
+	local_irq_save(irqflags);
+	intel_vblank_section_enter(dev_priv);
 
 	/* preempt_disable_rt() should go right here in PREEMPT_RT patchset. */
 
@@ -374,7 +401,8 @@ static bool i915_get_crtc_scanoutpos(struct drm_crtc *_crtc,
 
 	/* preempt_enable_rt() should go right here in PREEMPT_RT patchset. */
 
-	spin_unlock_irqrestore(&dev_priv->uncore.lock, irqflags);
+	intel_vblank_section_exit(dev_priv);
+	local_irq_restore(irqflags);
 
 	/*
 	 * While in vblank, position will be negative
@@ -412,9 +440,13 @@ int intel_get_crtc_scanline(struct intel_crtc *crtc)
 	unsigned long irqflags;
 	int position;
 
-	spin_lock_irqsave(&dev_priv->uncore.lock, irqflags);
+	local_irq_save(irqflags);
+	intel_vblank_section_enter(dev_priv);
+
 	position = __intel_get_crtc_scanline(crtc);
-	spin_unlock_irqrestore(&dev_priv->uncore.lock, irqflags);
+
+	intel_vblank_section_exit(dev_priv);
+	local_irq_restore(irqflags);
 
 	return position;
 }
@@ -537,7 +569,7 @@ void intel_crtc_update_active_timings(const struct intel_crtc_state *crtc_state,
 	 * Need to audit everything to make sure it's safe.
 	 */
 	spin_lock_irqsave(&i915->drm.vblank_time_lock, irqflags);
-	spin_lock(&i915->uncore.lock);
+	intel_vblank_section_enter(i915);
 
 	drm_calc_timestamping_constants(&crtc->base, &adjusted_mode);
 
@@ -546,7 +578,6 @@ void intel_crtc_update_active_timings(const struct intel_crtc_state *crtc_state,
 	crtc->mode_flags = mode_flags;
 
 	crtc->scanline_offset = intel_crtc_scanline_offset(crtc_state);
-
-	spin_unlock(&i915->uncore.lock);
+	intel_vblank_section_exit(i915);
 	spin_unlock_irqrestore(&i915->drm.vblank_time_lock, irqflags);
 }