From 80fa64d62067ea7390cd27d924dcb7c028e455e9 Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Tue, 17 Sep 2019 09:00:29 +0100 Subject: [PATCH] drm/i915: Only apply a rmw mmio update if the value changes 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 Signed-off-by: Chris Wilson Cc: Daniele Ceraolo Spurio Cc: Tvrtko Ursulin Reviewed-by: Mika Kuoppala Link: https://patchwork.freedesktop.org/patch/msgid/20190917080029.27632-1-chris@chris-wilson.co.uk --- 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 414fc2c..dcfa243 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, -- 2.7.4