linux-kernel - Re: [RFC PATCH 2/2] clocksource: dw_apb: allow build for architectures other than arm

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Date:	Thu, 20 Jun 2013 18:03:21 +0300
From:	Baruch Siach <baruch@...s.co.il>
To:	Pavel Machek <pavel@...x.de>
Cc:	John Stultz <john.stultz@...aro.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jamie Iles <jamie@...ieiles.com>,
	Dinh Nguyen <dinguyen@...era.com>
Subject: Re: [RFC PATCH 2/2] clocksource: dw_apb: allow build for
 architectures other than arm

Hi Pavel,

On Thu, Jun 20, 2013 at 04:44:33PM +0200, Pavel Machek wrote:
> > > >@@ -73,6 +77,9 @@ static void add_clocksource(struct device_node 
> > > >  *source_timer)
> > > >  }
> > > >  static void __iomem *sched_io_base;
> > > >+#ifndef CONFIG_HAVE_SETUP_SCHED_CLOCK
> > > >+static u64 sched_clock_mult __read_mostly;
> > > >+#endif
> > > >  static u32 read_sched_clock(void)
> > > >  {
> > > >@@ -97,7 +104,11 @@ static void init_sched_clock(void)
> > > >  	timer_get_base_and_rate(sched_timer, &sched_io_base, &rate);
> > > >  	of_node_put(sched_timer);
> > > >+#ifdef CONFIG_HAVE_SETUP_SCHED_CLOCK
> > > >  	setup_sched_clock(read_sched_clock, 32, rate);
> > > >+#else
> > > >+	sched_clock_mult = NSEC_PER_SEC / rate;
> > > >+#endif
> > > >  }
> > > 
> > > Can you rework this to not use #ifdefs within the function? They
> > > make it annoying to read the code.
> > > 
> > > Instead maybe have a local setup_sched_clock() function that sets
> > > the mult value for the !CONFIG_HAVE_SETUP_SCHED_CLOCK case?
> > > 
> > > >  static const struct of_device_id osctimer_ids[] __initconst = {
> > > >@@ -124,3 +135,10 @@ void __init dw_apb_timer_init(void)
> > > >  	init_sched_clock();
> > > >  }
> > > >+
> > > >+#ifndef CONFIG_HAVE_SETUP_SCHED_CLOCK
> > > >+unsigned long long notrace sched_clock()
> > > >+{
> > > >+	return read_sched_clock() * sched_clock_mult;
> > > >+}
> > > >+#endif
> > > 
> > > Also, can you try to condense the number of #ifndef
> > > CONFIG_HAVE_SETUP_SCHED_CLOCK checks to one, and consolidate the
> > > needed functions all in that one conditional?
> > 
> > Thanks for your comments. I'll rework the patch and resubmit.
> > 
> > I've just noticed that I have a bigger problem. read_sched_clock() returns 
> > u32, not u64. This means that in a rate of, say, 100MHz it will wrap around 
> > after a little more than 40 seconds. Would it make sense to put ARM's 32 bin 
> > sched_clock extension code (arch/arm/kernel/sched_clock.c) is a common place 
> > (maybe drivers/clocksource), and use that? There seems to be nothing ARM 
> > specific in this code, after all.
> 
> Also note that there are two conflicting changes to this area
> pending. It seems one in soc-next arm tree will prevail.
> 
> Please take a look...

Now that generic sched_clock implementation is available to all architectures 
(38ff87f77 "sched_clock: Make ARM's sched_clock generic for all architectures" 
in the timers/core branch of the tip tree) this patch is not needed anymore.

Thanks for the head up.

baruch

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