drm/i915: Replace WARN inside I915_READ64_2x32 with retry loop

Since we may conceivably encounter situations where the upper part of the
64bit register changes between reads, for example when a timestamp
counter overflows, change the WARN into a retry loop.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michał Winiarski <michal.winiarski@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 5f27290201e074c5d9a1673d710c96846b61c08c..fd1de451c8c6bae13f42eaae5e9cfe572039ea18 100644 (file)
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -3303,15 +3303,14 @@ int intel_freq_opcode(struct drm_i915_private *dev_priv, int val);
 #define I915_READ64(reg)       dev_priv->uncore.funcs.mmio_readq(dev_priv, (reg), true)
 
 #define I915_READ64_2x32(lower_reg, upper_reg) ({                      \
-               u32 upper = I915_READ(upper_reg);                       \
-               u32 lower = I915_READ(lower_reg);                       \
-               u32 tmp = I915_READ(upper_reg);                         \
-               if (upper != tmp) {                                     \
-                       upper = tmp;                                    \
-                       lower = I915_READ(lower_reg);                   \
-                       WARN_ON(I915_READ(upper_reg) != upper);         \
-               }                                                       \
-               (u64)upper << 32 | lower; })
+       u32 upper, lower, tmp;                                          \
+       tmp = I915_READ(upper_reg);                                     \
+       do {                                                            \
+               upper = tmp;                                            \
+               lower = I915_READ(lower_reg);                           \
+               tmp = I915_READ(upper_reg);                             \
+       } while (upper != tmp);                                         \
+       (u64)upper << 32 | lower; })
 
 #define POSTING_READ(reg)      (void)I915_READ_NOTRACE(reg)
 #define POSTING_READ16(reg)    (void)I915_READ16_NOTRACE(reg)