linux-kernel - Re: [PATCH v3 3/4] irq: Allow multiple clients to register for irq affinity notification

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Message-ID: <7hioka4dv7.fsf@deeprootsystems.com>
Date:	Fri, 26 Sep 2014 08:10:04 -0700
From:	Kevin Hilman <khilman@...nel.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Thomas Gleixner <tglx@...utronix.de>, ulf.hansson@...aro.org,
	linux-pm@...r.kernel.org, daniel.lezcano@...aro.org,
	rjw@...ysocki.net, linux-kernel@...r.kernel.org,
	Lina Iyer <lina.iyer@...aro.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 3/4] irq: Allow multiple clients to register for irq affinity notification

Russell King - ARM Linux <linux@....linux.org.uk> writes:

> On Fri, Sep 26, 2014 at 11:29:56AM +0200, Thomas Gleixner wrote:
>> On Thu, 25 Sep 2014, Kevin Hilman wrote:
>> > Maybe I'm missing something, or maybe we're just lucky and nobody uses
>> > them together, but irq_set_affinity_notifier() only allows a single
>> > notifier to be registered at any given time.  So if you had a system
>> 
>> A single notifier per irq .....
>
> So what about two drivers wanting to use this notifier, but sharing an
> interrupt?
>
> It sounds to me like this notifier was misdesigned from the very start,
> and it should always have supported multiple notifiers.

I agree.

$SUBJECT patch tries to add that support, and is part of a series
wanting to use these notifiers in the PM QoS subsystem, while at the
same time not breaking existing users.

I suppose this series could be written without $SUBJECT patch, and
crossing fingers in the hopes that an existing user of the notifiers
doesn't also need to use the pm_qos constraints, but that seems like
knowingly leaving an armed landmine laying around.

Kevin
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