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Date: Fri, 13 Feb 2015 11:01:18 +0800
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Subject: Re: [PATCH v2] clockevents: Introduce mode specific callbacks
From: Viresh Kumar <viresh.kumar@linaro.org>
To: "Rafael J. Wysocki" <rjw@rjwysocki.net>
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>,
        Peter Zijlstra <peterz@infradead.org>
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On 13 February 2015 at 10:11, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
> On Friday, February 13, 2015 08:54:56 AM Viresh Kumar wrote:
>> It is not possible for the clockevents core to know which modes (other than
>> those with a corresponding feature flag) are supported by a particular
>> implementation. And drivers are expected to handle transition to all modes
>> elegantly, as ->set_mode() would be issued for them unconditionally.
>>
>> Now, adding support for a new mode complicates things a bit if we want to use
>> the legacy ->set_mode() callback. We need to closely review all clockevents
>> drivers to see if they would break on addition of a new mode. And after such
>> reviews, it is found that we have to do non-trivial changes to most of the
>> drivers [1].
>>
>> Introduce mode-specific set_mode_*() callbacks, some of which the drivers may or
>> may not implement. A missing callback would clearly convey the message that the
>> corresponding mode isn't supported.
>
> This is not going to fly AFAICS if you don't say what exacly you need it for.

For this: https://lkml.org/lkml/2014/5/9/508