Re: [PATCH] clockevents: Add (missing) default case for switch blocks

From: Ingo Molnar
Date: Fri Feb 20 2015 - 05:52:28 EST

* Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:

> > So why is a 'default' mode needed then? It makes the
> > addition of new modes to the legacy handler easier,
> > which looks backwards.
> The requirement was to add another mode ONESHOT_STOPPED
> [1], to be supported only by the new per-mode callbacks..

Why would a callback need any flag, and why would a flag be
visible to old legacy callbacks?

> We have got a clear check in core with the patch Peter
> mentioned above, which doesn't let us call legacy
> ->set_mode() for the newer modes.
> if (dev->set_mode) {
> /* Legacy callback doesn't support new modes */
> return -ENOSYS;
> dev->set_mode(mode, dev);
> return 0;
> }

So here is where one of your problems comes from: why did
you add CLOCK_EVT_MODE_RESUME to the interface? Phase it
out, it's a legacy interface - new callbacks shouldn't need
any mode flags to begin with.

> > So I'm confused: if we are using proper callbacks (like
> > my example outlined) , why is a 'mode enum' needed at
> > all?
> The enum has two uses today:
> - pass mode to the legacy ->set_mode() callback, which
> isn't required for the new callbacks.

But this is misguided, as per above.

> - flag for clockevent core's internal state machine,
> which it would still require. For example, it checks
> new-mode != old-mode before changing the mode..

Internal state machine state should be decoupled from any
interface flags - especially when the interface is legacy.

> I believe the enum is still required for the state
> machine, even with new per-mode callbacks.

That needs to be fixed first then, before introducing new
API variants.


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