Re: [PATCH v3 1/4] drm/i915/psr: Clean-up intel_enable_source_psr1()

Jani Nikula
2017-07-14T09:29:28Z

On Wed, 12 Jul 2017, Chris Wilson <chris@chris-wilson.co.uk> wrote:
> Quoting Dhinakaran Pandiyan (2017-07-12 09:47:25)
>> On Tuesday, July 11, 2017 3:19:53 PM PDT Jim Bride wrote:
>> > On SKL+ there is a bit in SRD_CTL that software is not supposed to
>> > modify, but we currently clobber that bit when we enable PSR. In
>> > order to preserve the value of that bit, go ahead and read SRD_CTL
>>
>> And which bit is that?
>
> I think we would all be happier with keeping the explicit construction
> (and a smaller patch) if we used
>
> val |= I915_READ(EDP_PSR_CTL) & EDP_PSR_CTL_RSVD_MASK;

Agreed. Avoid read-modify-write as much as possible.

BR,
Jani.

--
Jani Nikula, Intel Open Source Technology Center