[U-Boot] [PATCH v2] mmc: omap: timeout counter fix

[Ghorai, Sukumar]

> -----Original Message-----
> From: u-boot-bounces at lists.denx.de [mailto:u-boot-bounces at lists.denx.de]
> On Behalf Of Wolfgang Denk
> Sent: Tuesday, October 26, 2010 10:59 AM
> To: Reinhard Meyer
> Cc: Menon, Nishanth; u-boot
> Subject: Re: [U-Boot] [PATCH v2] mmc: omap: timeout counter fix
> 
> Dear Reinhard Meyer,
> 
> In message <4CC62B6C.30601 at emk-elektronik.de> you wrote:
> >
> > In such cases I prefer to use:
> >
> > 	uint64_t etime;
> > ...
> > 	etime = get_ticks() + get_tbclk(); /* 1 second */
> > 	do {
> > 		whatever;
> > 		udelay (xx);
> > 	} while (condition && get_ticks() <= etime);
> >
> > That is far more accurate than calling udelay() 100000 times.
> 
> It may be more accuratre, but it may also be HORRIBLY WRONG!!
> 
> Do NOT do that!! NEVER implement such a delay loop as
> 
> 	end = time() + delay;
> 	while (time() < end)
> 		...
> 
> It fails in case the timer wraps around.
> 
> Assume 32 bit counters, start time = 0xFFFFFFF0, delay = 0x20. It
> will compute end = 0x10, the while codition is immediately false, and
> you don't have any delay at all, which most probably generates a
> false error condition.
> 
> 
> Correct implementation of a timeout like that should always look like
> that:
> 
> 	start = time();
> 	while ((time() - start) < delay)
> 		...
> 
> This works much better (assuming unsigned arithmetics).
[Ghorai] Thanks.. This is the best approach. 
Otherwise udelay() will increase the boot time. 

> 
> Best regards,
> 
> Wolfgang Denk
> 
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