Re: [PATCHv2 1/4] clockevents: Add generic timer broadcast receiver

[Mark Rutland]

On Mon, Jan 14, 2013 at 11:50:55AM +0000, Thomas Gleixner wrote:
> On Mon, 14 Jan 2013, Mark Rutland wrote:
> 
> > On Mon, Jan 14, 2013 at 11:06:31AM +0000, Thomas Gleixner wrote:
> > > On Wed, 9 Jan 2013, Mark Rutland wrote:
> > > > +#ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST
> > > > +extern int tick_receive_broadcast(void);
> > > > +#else
> > > > +static inline int tick_receive_broadcast(void)
> > > > +{
> > > > +	return 0;
> > > > +}
> > > 
> > > What's the inline function for? If an arch does not have broadcasting
> > > support it should not have a receive broadcast function call either.
> > 
> > That was how this was originally structured [1], but Santosh suggested this
> > would break the build for !GENERIC_CLOCKEVENTS_BROADCAST [1]. It means that the
> > arch-specific receive path (i.e. IPI handler) doesn't have to be #ifdef'd,
> > which makes it less ugly.
> 
> Hmm. If you want to keep the IPI around unconditionally the inline
> makes some sense, though the question is whether keeping an unused IPI
> around makes sense in the first place. I'd rather see a warning that
> an unexpected IPI happened than a silent inline function being called.

How about I add a warning (e.g. "Impossible timer broadcast received.") and
return -EOPNOTSUPP when !GENERIC_CLOCKEVENTS_BROADCAST?

> > > Is anything going to use the return value?
> > 
> > I'd added this after looking at the x86 lapic timers, where interrupts might
> > remain pending over a kexec, and lapic interrupts come up before timers are
> > registered. The return value is useful for shutting down the timer in that case
> > (see x86's local_apic_timer_interrupt).
> 
> Right, though then you need to check for evt->event_handler as well.

I thought this previously also [1], but I couldn't find any path such that a
tick_cpu_device would have an evtdev without an event_handler. We always set the
handler before setting evtdev, and alway wipe evtdev before wiping the handler.

Have I missed something?

> Thanks,
> 
> 	tglx
> 

Thanks,
Mark.

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2012-December/138092.html

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