Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> 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@xxxxxxxxx>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@xxxxxxxxx>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
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@xxxxxxxxxxxxxxx>
> ---
> 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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