linux-kernel - Re: [PATCH] clocksource: em

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Date:	Wed, 9 May 2012 02:06:32 +0900
From:	Magnus Damm <magnus.damm@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	linux-kernel@...r.kernel.org, horms@...ge.net.au, arnd@...db.de,
	linux-sh@...r.kernel.org, johnstul@...ibm.com, rjw@...k.pl,
	lethal@...ux-sh.org, gregkh@...uxfoundation.org, olof@...om.net
Subject: Re: [PATCH] clocksource: em_sti: Emma Mobile STI driver

Hi Thomas,

On Tue, May 8, 2012 at 4:10 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> On Thu, 3 May 2012, Magnus Damm wrote:
>> +/* private flags */
>> +#define FLAG_CLOCKEVENT (1 << 0)
>> +#define FLAG_CLOCKSOURCE (1 << 1)
>> +
>> +static int em_sti_start(struct em_sti_priv *p, unsigned long flag)
>> +{
>> +     int ret = 0;
>> +     unsigned long flags;
>> +
>> +     spin_lock_irqsave(&p->lock, flags);
>> +
>> +     if (!(p->flags & (FLAG_CLOCKEVENT | FLAG_CLOCKSOURCE)))
>> +             ret = em_sti_enable(p);
>
> That's confusing. You seem to enable both CLOCKEVENT and CLOCKSOURCE
> independent of "flag" value.

Hm, I believe the idea is to check if it has been enabled already...

>> +
>> +     if (!ret)
>> +             p->flags |= flag;
>
> And then just or "flag" ??????

... but it certainly is overly complicated. I'll rework it into
something that is easier to digest. =)

>> +     spin_unlock_irqrestore(&p->lock, flags);
>> +
>> +     return ret;
>> +}
>> +
>> +static void em_sti_stop(struct em_sti_priv *p, unsigned long flag)
>> +{
>> +     unsigned long flags;
>> +     unsigned long f;
>> +
>> +     spin_lock_irqsave(&p->lock, flags);
>> +
>> +     f = p->flags & (FLAG_CLOCKEVENT | FLAG_CLOCKSOURCE);
>> +     p->flags &= ~flag;
>> +
>> +     if (f && !(p->flags & (FLAG_CLOCKEVENT | FLAG_CLOCKSOURCE)))
>> +             em_sti_disable(p);
>
> Huch? If the caller wants to disable the clockevent, you stop the
> clocksource as well because em_sti_disable() stops the clock.
>
> /me is confused.

I believe the idea is that if the timer is currently enabled (f) and
if we are the last user thenthen stop.

A regular usage counter probably makes much more sense!

>> +static void em_sti_clock_event_start(struct em_sti_priv *p)
>> +{
>> +     struct clock_event_device *ced = &p->ced;
>> +
>> +     em_sti_start(p, FLAG_CLOCKEVENT);
>> +
>> +     /* TODO: calculate good shift from rate and counter bit width */
>> +
>> +     ced->shift = 32;
>> +     ced->mult = div_sc(p->rate, NSEC_PER_SEC, ced->shift);
>
> IIRC, we have a generic function to do that :)

Ok, thanks for pointing that out. Need to look it up!

Will update and post a V2. Thanks for your help!

Cheers,

/ magnus
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