[Intel-gfx] [PATCH 1/2] i915/uncore: Acquire fw before loop in intel_uncore_read64_2x32

[Umesh Nerlige Ramappa]

PMU reads the GT timestamp as a 2x32 mmio read and since upper and lower
32 bit registers are read in a loop, there is a latency involved between
getting the GT timestamp and the CPU timestamp. As part of the
resolution, refactor intel_uncore_read64_2x32 to acquire forcewake and
uncore lock prior to reading upper and lower regs.

Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa at intel.com>
---
 drivers/gpu/drm/i915/intel_uncore.h | 44 ++++++++++++++++++++---------
 1 file changed, 30 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_uncore.h b/drivers/gpu/drm/i915/intel_uncore.h
index 5449146a0624..e9e38490815d 100644
--- a/drivers/gpu/drm/i915/intel_uncore.h
+++ b/drivers/gpu/drm/i915/intel_uncore.h
@@ -382,20 +382,6 @@ __uncore_write(write_notrace, 32, l, false)
  */
 __uncore_read(read64, 64, q, true)
 
-static inline u64
-intel_uncore_read64_2x32(struct intel_uncore *uncore,
-			 i915_reg_t lower_reg, i915_reg_t upper_reg)
-{
-	u32 upper, lower, old_upper, loop = 0;
-	upper = intel_uncore_read(uncore, upper_reg);
-	do {
-		old_upper = upper;
-		lower = intel_uncore_read(uncore, lower_reg);
-		upper = intel_uncore_read(uncore, upper_reg);
-	} while (upper != old_upper && loop++ < 2);
-	return (u64)upper << 32 | lower;
-}
-
 #define intel_uncore_posting_read(...) ((void)intel_uncore_read_notrace(__VA_ARGS__))
 #define intel_uncore_posting_read16(...) ((void)intel_uncore_read16_notrace(__VA_ARGS__))
 
@@ -455,6 +441,36 @@ static inline void intel_uncore_rmw_fw(struct intel_uncore *uncore,
 		intel_uncore_write_fw(uncore, reg, val);
 }
 
+static inline u64
+intel_uncore_read64_2x32(struct intel_uncore *uncore,
+			 i915_reg_t lower_reg, i915_reg_t upper_reg)
+{
+	u32 upper, lower, old_upper, loop = 0;
+	enum forcewake_domains fw_domains;
+	unsigned long flags;
+
+	fw_domains = intel_uncore_forcewake_for_reg(uncore, lower_reg,
+						    FW_REG_READ);
+
+	fw_domains |= intel_uncore_forcewake_for_reg(uncore, upper_reg,
+						    FW_REG_READ);
+
+	spin_lock_irqsave(&uncore->lock, flags);
+	intel_uncore_forcewake_get__locked(uncore, fw_domains);
+
+	upper = intel_uncore_read_fw(uncore, upper_reg);
+	do {
+		old_upper = upper;
+		lower = intel_uncore_read_fw(uncore, lower_reg);
+		upper = intel_uncore_read_fw(uncore, upper_reg);
+	} while (upper != old_upper && loop++ < 2);
+
+	intel_uncore_forcewake_put__locked(uncore, fw_domains);
+	spin_unlock_irqrestore(&uncore->lock, flags);
+
+	return (u64)upper << 32 | lower;
+}
+
 static inline int intel_uncore_write_and_verify(struct intel_uncore *uncore,
 						i915_reg_t reg, u32 val,
 						u32 mask, u32 expected_val)
-- 
2.36.1