If we try to clear, or even set, a bit in the register that doesn't
change the register state; skip the write. There's a slight danger in
that the register acts as a latch-on-write, but I do not think we use a
rmw cycle with any such latch registers.
Suggested-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@xxxxxxxxx>
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@xxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
---
drivers/gpu/drm/i915/intel_uncore.h | 20 ++++++++++----------
1 file changed, 10 insertions(+), 10 deletions(-)
diff --git a/drivers/gpu/drm/i915/intel_uncore.h b/drivers/gpu/drm/i915/intel_uncore.h
index 414fc2cb0459..dcfa243892c6 100644
--- a/drivers/gpu/drm/i915/intel_uncore.h
+++ b/drivers/gpu/drm/i915/intel_uncore.h
@@ -378,23 +378,23 @@ intel_uncore_read64_2x32(struct intel_uncore *uncore,
static inline void intel_uncore_rmw(struct intel_uncore *uncore,
i915_reg_t reg, u32 clear, u32 set)
{
- u32 val;
+ u32 old, val;
- val = intel_uncore_read(uncore, reg);
- val &= ~clear;
- val |= set;
- intel_uncore_write(uncore, reg, val);
+ old = intel_uncore_read(uncore, reg);
+ val = (old & ~clear) | set;
+ if (val != old)
+ intel_uncore_write(uncore, reg, val);
}
static inline void intel_uncore_rmw_fw(struct intel_uncore *uncore,
i915_reg_t reg, u32 clear, u32 set)
{
- u32 val;
+ u32 old, val;
- val = intel_uncore_read_fw(uncore, reg);
- val &= ~clear;
- val |= set;
- intel_uncore_write_fw(uncore, reg, val);
+ old = intel_uncore_read_fw(uncore, reg);
+ val = (old & ~clear) | set;
+ if (val != old)
+ intel_uncore_write_fw(uncore, reg, val);
}
static inline int intel_uncore_write_and_verify(struct intel_uncore *uncore,
--
2.23.0
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