• Viresh Kumar's avatar
    clockevents: Introduce mode specific callbacks · bd624d75
    Viresh Kumar authored
    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.
    
    A driver may still choose to keep supporting the legacy ->set_mode() callback,
    but ->set_mode() wouldn't be supporting any new modes beyond RESUME. If a driver
    wants to benefit from using a new mode, it would be required to migrate to
    the mode specific callbacks.
    
    The legacy ->set_mode() callback and the newly introduced mode-specific
    callbacks are mutually exclusive. Only one of them should be supported by the
    driver.
    
    Sanity check is done at the time of registration to distinguish between optional
    and required callbacks and to make error recovery and handling simpler. If the
    legacy ->set_mode() callback is provided, all mode specific ones would be
    ignored by the core but a warning is thrown if they are present.
    
    Call sites calling ->set_mode() directly are also updated to use
    __clockevents_set_mode() instead, as ->set_mode() may not be available anymore
    for few drivers.
    
     [1] https://lkml.org/lkml/2014/12/9/605
     [2] https://lkml.org/lkml/2015/1/23/255
    
    Suggested-by: Thomas Gleixner <tglx@linutronix.de> [2]
    Signed-off-by: default avatarViresh Kumar <viresh.kumar@linaro.org>
    Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
    Cc: Frederic Weisbecker <fweisbec@gmail.com>
    Cc: John Stultz <john.stultz@linaro.org>
    Cc: Kevin Hilman <khilman@linaro.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com>
    Cc: linaro-kernel@lists.linaro.org
    Cc: linaro-networking@linaro.org
    Link: http://lkml.kernel.org/r/792d59a40423f0acffc9bb0bec9de1341a06fa02.1423788565.git.viresh.kumar@linaro.orgSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    bd624d75
timer_list.c 9.6 KB