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

From: Hector Martin <marcan@marcan.st>
To: Viresh Kumar <viresh.kumar@linaro.org>,
	Sibi Sankar <sibis@codeaurora.org>,
	Saravana Kannan <saravanak@google.com>
Cc: linux-arm-kernel@lists.infradead.org,
	Alyssa Rosenzweig <alyssa@rosenzweig.io>,
	Sven Peter <sven@svenpeter.dev>, Marc Zyngier <maz@kernel.org>,
	Mark Kettenis <mark.kettenis@xs4all.nl>,
	Michael Turquette <mturquette@baylibre.com>,
	Stephen Boyd <sboyd@kernel.org>, Rob Herring <robh+dt@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>,
	Viresh Kumar <vireshk@kernel.org>, Nishanth Menon <nm@ti.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Kevin Hilman <khilman@kernel.org>,
	Ulf Hansson <ulf.hansson@linaro.org>,
	linux-clk@vger.kernel.org, devicetree@vger.kernel.org,
	linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 4/9] opp: core: Don't warn if required OPP device does not exist
Date: Tue, 12 Oct 2021 14:57:50 +0900	[thread overview]
Message-ID: <caf16a6c-f127-7f27-ed17-0522d9f1fb9e@marcan.st> (raw)
In-Reply-To: <20211012055143.xmkbvhbnolspgjin@vireshk-i7>

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@marcan.st)
Public Key: https://mrcn.st/pub