linux-kernel - Re: [PATCH v2 6/10] cpufreq: Support for fast frequency switching

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Message-ID: <56DA2152.2080207@linaro.org>
Date:	Fri, 4 Mar 2016 15:59:14 -0800
From:	Steve Muckle <steve.muckle@...aro.org>
To:	"Rafael J. Wysocki" <rafael@...nel.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Juri Lelli <juri.lelli@....com>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Michael Turquette <mturquette@...libre.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH v2 6/10] cpufreq: Support for fast frequency switching

On 03/04/2016 02:58 PM, Rafael J. Wysocki wrote:
>>> How about modifying cpufreq_register_notifier to return an error if the
>>> >> driver has a fast_switch callback installed and an attempt to register a
>>> >> transition notifier is made?
>> >
>> > That sounds like a good idea.
>
> Transition notifiers may be registered before the driver is
> registered, so that won't help in all cases.

Could that hole be closed by a similar check in
cpufreq_register_driver()? I.e. if the transition_notifier list is not
empty, fail to register the driver (if the driver has a fast_switch
routine)?

Or alternatively, the fast_switch routine is not installed.

thanks,
Steve