Messages in this thread | | | Date | Fri, 20 Feb 2015 09:48:07 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH] clockevents: Add (missing) default case for switch blocks |
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On Fri, Feb 20, 2015 at 09:38:42AM +0100, Ingo Molnar wrote: > > * Viresh Kumar <viresh.kumar@linaro.org> wrote: > > > Many clockevent drivers are using a switch block for handling modes in their > > ->set_mode() callback. Some of these do not have a 'default' case and adding a > > new mode in the 'enum clock_event_mode', starts giving following warnings for > > these platforms about unhandled modes (e.g. XXX). > > > > warning: enumeration value ‘XXX’ not handled in switch [-Wswitch] > > > > This patch adds default cases for them. > > > > In order to keep things simple, add following to the switch blocks: > > > > default: > > break; > > > > This can lead to different behavior for individual cases. > > > > 1) Some of the drivers don't have any special stuff in their ->set_mode() > > callback before or after the switch blocks. And so this default case would > > simply return for them without any updates to the clockevent device. > > > > 2) But in some cases, the clockevent device is disabled/stopped as soon as we > > enter the ->set_mode() callback and is enabled within the switch block or > > after it. And the clockevent device *may* stay disabled for default case. > > So this whole approach looks fragile for several reasons: > > - 'mode setting' callbacks are just bad by design > because they mix several functions into the same entry > point, complicating the handler functions > unnecessarily. We should reduce complexity, not expand > on it. > > - now by adding 'default' you hide from drivers the > ability to easily discover whether it has been updated > to some new core clockevents mode setting feature or > not.
So this patch was a follow on from bd624d75db21 ("clockevents: Introduce mode specific callbacks").
That patch changes the set_mode() interface; and provides per mode functions.
New (and updated) drivers should not use ->set_mode() anymore, but it was felt that we do not want to go do flag day changes.
And it allows for adding optional modes; not every driver needs to go implement all mode functions if there is a sane default action.
But it does mean we need to be able to add values to the enum.
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