linux-kernel - Re: [PATCH 06/27] score: create head files delay.h device.h div64.h dma-mapping.h dma.h

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Date:	Sun, 14 Jun 2009 00:31:54 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	liqin.chen@...plusct.com
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org
Subject: Re: [PATCH 06/27] score: create head files delay.h device.h div64.h dma-mapping.h dma.h

On Saturday 13 June 2009, liqin.chen@...plusct.com wrote:
> Arnd Bergmann <arnd@...db.de> 写于 2009-06-10 01:18:20:
> 
> > On Tuesday 09 June 2009, liqin.chen@...plusct.com wrote:
> > 
> > Having a working udelay() function is required for many
> > drivers that are sensitive to timing, you should probably
> > implement that at some point in the future.
> 
> Add udelay() implement in code.

so you use 

static inline void __delay(unsigned long loops)
{
        __asm__ __volatile__ (
                "1:\tsubi\t%0,1\n\t"
                "cmpz.c\t%0\n\t"
                "bne\t1b\n\t"
                : "=r" (loops)
                : "0" (loops));
}

static inline void __udelay(unsigned long usecs)
{
        __delay(usecs);
}


This is much better than before, but is far from exact in the __udelay()
case. Please take a look at init/calibrate.c and how other architectures
use loops_per_jiffy if you don't have an exact time source you can use.

If you have a time source with microsecond resolution or better, just loop
until the amount of microseconds has expired.

	Arnd <><
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