[Intel-gfx] [PATCH 4/6] drm/i915: Serialize all register access

[Chris Wilson]

In theory, the different register blocks were meant to be only ever
touched when holding either the struct_mutex, mode_config.lock or even a
specific localised lock. This does not seem to be the case, and the
hardware reacts extremely badly if we attempt to concurrently access two
registers within the same cacheline.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=63914
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/intel_gt.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_gt.c b/drivers/gpu/drm/i915/intel_gt.c
index 257a2e9..9eeaefb 100644
--- a/drivers/gpu/drm/i915/intel_gt.c
+++ b/drivers/gpu/drm/i915/intel_gt.c
@@ -339,21 +339,21 @@ hsw_unclaimed_reg_check(struct drm_i915_private *dev_priv, u32 reg)
 
 #define __i915_read(x, y) \
 u##x i915_read##x(struct drm_i915_private *dev_priv, u32 reg, bool trace) { \
+	unsigned long irqflags; \
 	u##x val = 0; \
+	spin_lock_irqsave(&dev_priv->gt_lock, irqflags); \
 	if (IS_GEN5(dev_priv->dev)) \
 		ilk_dummy_write(dev_priv); \
 	if (NEEDS_FORCE_WAKE((dev_priv), (reg))) { \
-		unsigned long irqflags; \
-		spin_lock_irqsave(&dev_priv->gt_lock, irqflags); \
 		if (dev_priv->forcewake_count == 0) \
 			dev_priv->gt.force_wake_get(dev_priv); \
 		val = read##y(dev_priv->regs + reg); \
 		if (dev_priv->forcewake_count == 0) \
 			dev_priv->gt.force_wake_put(dev_priv); \
-		spin_unlock_irqrestore(&dev_priv->gt_lock, irqflags); \
 	} else { \
 		val = read##y(dev_priv->regs + reg); \
 	} \
+	spin_unlock_irqrestore(&dev_priv->gt_lock, irqflags); \
 	if (trace) trace_i915_reg_rw(false, reg, val, sizeof(val)); \
 	return val; \
 }
@@ -366,8 +366,10 @@ __i915_read(64, q)
 
 #define __i915_write(x, y) \
 void i915_write##x(struct drm_i915_private *dev_priv, u32 reg, u##x val, bool trace) { \
+	unsigned long irqflags; \
 	u32 __fifo_ret = 0; \
 	if (trace) trace_i915_reg_rw(true, reg, val, sizeof(val)); \
+	spin_lock_irqsave(&dev_priv->gt_lock, irqflags); \
 	if (NEEDS_FORCE_WAKE((dev_priv), (reg))) { \
 		__fifo_ret = __gen6_gt_wait_for_fifo(dev_priv); \
 	} \
@@ -379,6 +381,7 @@ void i915_write##x(struct drm_i915_private *dev_priv, u32 reg, u##x val, bool tr
 		gen6_gt_check_fifodbg(dev_priv); \
 	} \
 	hsw_unclaimed_reg_check(dev_priv, reg); \
+	spin_unlock_irqrestore(&dev_priv->gt_lock, irqflags); \
 }
 __i915_write(8, b)
 __i915_write(16, w)
-- 
1.8.3.2