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

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Date:   Fri, 26 Aug 2022 10:56:12 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...nel.org>, linux-arm-msm@...r.kernel.org,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH] opp: Expose voltage info in debugfs for OPPs w/out
 explicit regulators

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@...omium.org>

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