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>

1 files changed, 8 insertions, 9 deletions

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 5f27290201e0..fd1de451c8c6 100644
--- 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)