linux-kernel - Re: [PATCH] clockevents: Introduce mode specific callbacks

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Message-ID: <20150211103845.GR23123@twins.programming.kicks-ass.net>
Date:	Wed, 11 Feb 2015 11:38:45 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Linaro Kernel Mailman List <linaro-kernel@...ts.linaro.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kevin Hilman <khilman@...aro.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Linaro Networking <linaro-networking@...aro.org>
Subject: Re: [PATCH] clockevents: Introduce mode specific callbacks

On Wed, Feb 11, 2015 at 11:24:53AM +0800, Viresh Kumar wrote:
> On 10 February 2015 at 22:15, Peter Zijlstra <peterz@...radead.org> wrote:
> > On Wed, Feb 04, 2015 at 01:06:23PM +0530, Viresh Kumar wrote:
> >> +     /*
> >> +      * Mode transition callback(s): Only one of the two groups should be
> >> +      * defined:
> >> +      * - set_mode(), only for modes <= CLOCK_EVT_MODE_RESUME.
> >> +      * - set_mode_{shutdown|periodic|oneshot|resume}().
> >> +      */

> >> +static int clockevents_sanity_check(struct clock_event_device *dev)
> >> +{
> >> +}
> >
> > It appears to me you've not actually checked that condition outlined
> > above, a driver could set both the legacy and the new callbacks.
> 
> Exactly for this reason I mentioned this in the logs:
> 
> >> If the legacy ->set_mode() callback is provided, all mode specific
> >> callbacks would be ignored.
> 
> So, either we can mention that in the code as well OR add code to
> check and WARN about that. Will do whatever looks better to you
> guys.

I think its better to be strict; esp. with new interfaces. It avoids
confusion.

Suppose a driver writer sees these new methods and thinks to use one
while still having the set_mode() one -- ie. he didn't actually read the
comment. We'd better make sure he fails and goes back to read it.
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