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

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Date:	Fri, 20 Feb 2015 14:22:20 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Linaro Kernel Mailman List <linaro-kernel@...ts.linaro.org>,
	Kevin Hilman <khilman@...aro.org>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Linaro Networking <linaro-networking@...aro.org>,
	Steven Miao <realmz6@...il.com>,
	Mark Salter <msalter@...hat.com>,
	Michal Simek <monstr@...str.eu>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Ley Foon Tan <lftan@...era.com>,
	Jonas Bonn <jonas@...thpole.se>,
	"David S. Miller" <davem@...emloft.net>,
	Jeff Dike <jdike@...toit.com>,
	Guan Xuetao <gxt@...c.pku.edu.cn>
Subject: Re: [PATCH] clockevents: Add (missing) default case for switch blocks


* Viresh Kumar <viresh.kumar@...aro.org> wrote:

> On 20 February 2015 at 17:11, Ingo Molnar <mingo@...nel.org> wrote:
> >
> > * Peter Zijlstra <peterz@...radead.org> wrote:
> 
> >> Maybe we should break that enum into two; one for devices
> >> and one for the core interface and avoid the problem that
> >> way.
> >
> > Yeah, that would do the trick.
> 
> Thanks for your suggestions. Just to confirm (before I spam lists with
> patches), is
> this somewhat similar to what you are looking for ?
> 
> diff --git a/include/linux/clockchips.h b/include/linux/clockchips.h
> index 59af26b54d15..80b669cb836d 100644
> --- a/include/linux/clockchips.h
> +++ b/include/linux/clockchips.h
> @@ -32,17 +32,24 @@ enum clock_event_nofitiers {
>  struct clock_event_device;
>  struct module;
> 
> -/* Clock event mode commands */
> +/* Clock event mode commands for legacy ->set_mode(): OBSOLETE */
>  enum clock_event_mode {
>         CLOCK_EVT_MODE_UNUSED = 0,
>         CLOCK_EVT_MODE_SHUTDOWN,
>         CLOCK_EVT_MODE_PERIODIC,
>         CLOCK_EVT_MODE_ONESHOT,
>         CLOCK_EVT_MODE_RESUME,
> -
> -       /* Legacy ->set_mode() callback doesn't support below modes */
>  };
> 
> +/* Clock event modes, only for core's internal use */
> +enum clock_event_dev_mode {
> +       CLOCK_EVT_DEV_MODE_UNUSED = 0,

What is 'unused' - not initialized yet?

> +       CLOCK_EVT_DEV_MODE_SHUTDOWN,
> +       CLOCK_EVT_DEV_MODE_PERIODIC,
> +       CLOCK_EVT_DEV_MODE_ONESHOT,
> +       CLOCK_EVT_DEV_MODE_RESUME,

What is 'resume' mode?

> +       CLOCK_EVT_DEV_MODE_ONESHOT_STOPPED,  /* This would be the new
> mode which I will add later */

What does this mode express?

So for state machines it's important to document the states 
and the transitions between them very clearly - please 
start with that.

> +};

Also, this should not be in a generic header, it should be 
somewhere internal in kernel/time/.

> Ofcourse, we also need to replace 'clock_event_mode' with 
> 'clock_event_dev_mode' and 'CLOCK_EVT_MODE_*' with 
> 'CLOCK_EVT_DEV_MODE_*' in all core code..

Yes.

Thanks,

	Ingo
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