linux-kernel - Re: [PATCH v2 19/29] nios2: Time keeping

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Date:	Mon, 21 Jul 2014 18:07:02 +0800
From:	Ley Foon Tan <lftan@...era.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Linux-Arch <linux-arch@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	Chung-Lin Tang <cltang@...esourcery.com>
Subject: Re: [PATCH v2 19/29] nios2: Time keeping

On Tue, Jul 15, 2014 at 5:45 PM, Arnd Bergmann <arnd@...db.de> wrote:
> On Tuesday 15 July 2014 16:45:46 Ley Foon Tan wrote:
>> +
>> +static inline void __delay(unsigned long loops)
>> +{
>> +     int dummy;
>> +
>> +     __asm__ __volatile__(
>> +     "1:\n\t"
>> +     "    beq    %0,zero,2f\n\t"
>> +     "    addi   %0, %0, -1\n\t"
>> +     "    br     1b\n\t"
>> +     "2:\n\t"
>> +     :  "=r" (dummy)         /* Need output for optimizer */
>> +     :  "0" (loops));        /* %0  Input */
>> +}
>
> Do you have a reliable clock source? If you do, it would be better
> to replace the delay loop with an implementation that waits for
> the exact time to pass instead. This will also avoid the loop
> calibration during boot and give you better boot times.
Okay, will change this to use timer instead.

>
>> +#ifndef _ASM_NIOS2_TIMEX_H
>> +#define _ASM_NIOS2_TIMEX_H
>> +
>> +/* Supply dummy tick-rate. Real value will be read from devicetree */
>> +#define CLOCK_TICK_RATE              (HZ * 100000UL)
>> +
>> +#include <asm-generic/timex.h>
>> +
>> +#endif
>
> CLOCK_TICK_RATE is no longer used anywhere, no need for this file.

I found jiffies.h still using this define. Can we still remove this?
In include/linux/jiffies.h:
#define LATCH ((CLOCK_TICK_RATE + HZ/2) / HZ)   /* For divider */

>
>> diff --git a/arch/nios2/kernel/time.c b/arch/nios2/kernel/time.c
>> new file mode 100644
>> index 0000000..111ade1
>> --- /dev/null
>> +++ b/arch/nios2/kernel/time.c
>
> Maybe move this to drivers/clocksource? Same argument as for the
> irqchip driver, so either move both or neither.
Will keep this here since we don't move irq driver.

Thanks.

Regards
Ley Foon
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