| Message ID | 20190917080029.27632-1-chris@chris-wilson.co.uk (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | drm/i915: Only apply a rmw mmio update if the value changes | expand |
Chris Wilson <chris@chris-wilson.co.uk> writes: > 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@intel.com> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> > Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com> > Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> My stance was that with clear ~0, user should be notified. But I guess on this level of tooling, you should be free to do the useless read. Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com> > --- > 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 > > _______________________________________________ > Intel-gfx mailing list > Intel-gfx@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
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,
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@intel.com> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> --- drivers/gpu/drm/i915/intel_uncore.h | 20 ++++++++++---------- 1 file changed, 10 insertions(+), 10 deletions(-)