linux-kernel - Re: [RFC PATCH 4/9] opp: core: Don't warn if required OPP device does not exist

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Date:   Tue, 12 Oct 2021 14:57:50 +0900
From:   Hector Martin <marcan@...can.st>
To:     Viresh Kumar <viresh.kumar@...aro.org>,
        Sibi Sankar <sibis@...eaurora.org>,
        Saravana Kannan <saravanak@...gle.com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Sven Peter <sven@...npeter.dev>, Marc Zyngier <maz@...nel.org>,
        Mark Kettenis <mark.kettenis@...all.nl>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
        Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Catalin Marinas <catalin.marinas@....com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Kevin Hilman <khilman@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        linux-clk@...r.kernel.org, devicetree@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 4/9] opp: core: Don't warn if required OPP device does
 not exist

On 12/10/2021 14.51, Viresh Kumar wrote:
> On 12-10-21, 14:34, Hector Martin wrote:
>> The table *is* assigned to a genpd (the memory controller), it's just that
>> that genpd isn't actually a parent of the CPU device. Without the patch you
>> end up with:
>>
>> [    3.040060] cpu cpu4: Failed to set performance rate of cpu4: 0 (-19)
>> [    3.042881] cpu cpu4: Failed to set required opps: -19
>> [    3.045508] cpufreq: __target_index: Failed to change cpu frequency: -19
> 
> Hmm, Saravana and Sibi were working on a similar problem earlier and decided to
> solve this using devfreq instead. Don't remember the exact series which got
> merged for this, Sibi ?
> 
> If this part fails, how do you actually set the performance state of the memory
> controller's genpd ?

The clock controller has the genpd as an actual power-domain parent, so 
it does it instead. From patch #7:

> +	if (cluster->has_pd)
> +		dev_pm_genpd_set_performance_state(cluster->dev,
> +						   dev_pm_opp_get_required_pstate(opp, 0));
> +

This is arguably not entirely representative of how the hardware works, 
since technically the cluster switching couldn't care less what the 
memory controller is doing; it's a soft dependency, states that should 
be switched together but are not interdependent (in fact, the clock code 
does this unconditionally after the CPU p-state change, regardless of 
whether we're shifting up or down; this is, FWIW, the same order macOS 
uses, and it clearly doesn't matter which way you do it).

-- 
Hector Martin (marcan@...can.st)
Public Key: https://mrcn.st/pub