From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1752373AbbBKKiy (ORCPT <rfc822;w@1wt.eu>);
	Wed, 11 Feb 2015 05:38:54 -0500
Received: from bombadil.infradead.org ([198.137.202.9]:51358 "EHLO
	bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751075AbbBKKix (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Wed, 11 Feb 2015 05:38:53 -0500
Date: Wed, 11 Feb 2015 11:38:45 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
        Linaro Kernel Mailman List <linaro-kernel@lists.linaro.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Kevin Hilman <khilman@linaro.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Preeti U Murthy <preeti@linux.vnet.ibm.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Linaro Networking <linaro-networking@linaro.org>
Subject: Re: [PATCH] clockevents: Introduce mode specific callbacks
Message-ID: <20150211103845.GR23123@twins.programming.kicks-ass.net>
References: <025ca1872df9ed8a9f7b6e0400e71ed296374183.1423034839.git.viresh.kumar@linaro.org>
 <20150210141541.GB7119@twins.programming.kicks-ass.net>
 <CAKohpomhTO=ZaOAm8Q4dyX0=1vYOktm_y=u-++dNtgGm8j172A@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAKohpomhTO=ZaOAm8Q4dyX0=1vYOktm_y=u-++dNtgGm8j172A@mail.gmail.com>
User-Agent: Mutt/1.5.21 (2012-12-30)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Wed, Feb 11, 2015 at 11:24:53AM +0800, Viresh Kumar wrote:
> On 10 February 2015 at 22:15, Peter Zijlstra <peterz@infradead.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.