Re: [PATCH] opp: Expose voltage info in debugfs for OPPs w/out explicit regulators

[Matthias Kaehlcke <mka@chromium.org>]

On Fri, Aug 26, 2022 at 07:56:59AM -0700, Douglas Anderson wrote:
> On some cpufreq drivers we know the voltage associated with each
> operating point but there is no explicit Linux "regulator" present. An
> example is "qcom-cpufreq-hw.c". There the voltage is managed
> automatically by the hardware but we still associate it with the OPP
> table so we can do energy calculations for EAS.
> 
> The OPP framework handles this in general. In _opp_allocate() it can
> be seen that we always allocate space for one supply even if
> "regulator_count" is 0.
> 
> Let's handle this properly in debugfs.
> 
> NOTE: as a side effect of this a whole bunch of OPPs in the system may
> get supply-related files exposed in debugfs that are mostly useless
> (they'll just contain 0). I'd expect this to be OK but it's moderately
> annoying. It seems better than trying to dynamically create debugfs
> directories when the voltages are non-zero or adding extra complexity
> in the code giving a hint to the OPP framework that voltages should be
> exposed.
> 
> After this patch, on a sc7180-trogdor class device I can see voltages
> for the CPU OPPs under /sys/kernel/debug/opp.
> 
> Fixes: dfbe4678d709 ("PM / OPP: Add infrastructure to manage multiple regulators")
> Signed-off-by: Douglas Anderson <dianders@chromium.org>

Reviewed-by: Matthias Kaehlcke <mka@chromium.org>