linux-kernel - Re: [PATCH v5 21/29] nios2: Time keeping

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Message-ID: <1806277.3CF96bVORX@wuerfel>
Date:	Tue, 28 Oct 2014 10:23:37 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Ley Foon Tan <lftan@...era.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	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 v5 21/29] nios2: Time keeping

On Tuesday 28 October 2014 10:46:29 Ley Foon Tan wrote:
> On Sun, Oct 26, 2014 at 5:10 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> > On Fri, 24 Oct 2014, Ley Foon Tan wrote:
> >> +#ifndef _ASM_NIOS2_TIMEX_H
> >> +#define _ASM_NIOS2_TIMEX_H
> >> +
> >> +typedef unsigned long cycles_t;
> >> +
> >> +extern cycles_t get_cycles(void);
> >> +
> >> +#define ARCH_HAS_READ_CURRENT_TIMER
> >
> > Why does NIOS need that? Does it have a hardware implementation
> > dependent clock frequency which needs to be calibrated at boot time?
> This is suggestion from Arnd to use read_current_timer instead of using
> expensive delay loop calibration during boot.

My mistake, sorry. I think the right way is to define
calibrate_delay_is_known() rather than read_current_timer(), I was
getting confused by the ARM implementation that does both.

	Arnd
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