[U-Boot-Users] [PATCH 3/5] OneNAND support

[Kyungmin Park]

> -----Original Message-----
> From: wd at denx.de [mailto:wd at denx.de]
> Sent: Monday, September 10, 2007 4:07 PM
> To: kmpark at infradead.org
> Cc: u-boot-users at lists.sourceforge.net
> Subject: Re: [U-Boot-Users] [PATCH 3/5] OneNAND support
> 
> In message <002501c7f347$e1d579c0$e1ac580a at swcenter.sec.samsung.co.kr> you wrote:
> > > ...
> > > > +#ifdef __ARM__
> > > > +extern void memcpy32(void *, void *, size_t);
> > > > +
> > > > +static void *memcpy(void *dest, const void *src, size_t count)
> > > > +{
> > > > +	if (count < 32) {
> > > > +		unsigned short *_s = (unsigned short *)(src);
> > > > +		unsigned short *_d = (unsigned short *)(dest);
> > > > +		count >>= 1;
> > > > +		while (count--)
> > > > +			*_d++ = *_s++;
> > > > +		return _d;
> > > > +	}
> > > > +
> > > > +	memcpy32(dest, (void *)src, count);
> > > > +
> > > > +	return (void *)count;
> > > > +}
> > > > +#endif
> > >
> > > Why exactly do we need this? And why do we need an additonal  special
> > > function memcpy32?
> >
> > It's for performance. Now ARM used the char-based memcpy. Even though it's working with current
> char-based memcpy, I want to use the
> > optimized memcpy.
> 
> How much difference does this optimization make in real life? Do you
> have any time measurements at hand?

It's also discuss the at previous time
http://sourceforge.net/mailarchive/message.php?msg_id=f3f1b91a0703141856n1807b799pfd8ffb4783ff0804%40mail.gmail.com

> 
> I'm concerned about correctness. What happens in your coide when I
> write
> 
> 	memcpy (dst, src, 5);
> 
> How many bytes will be copied?
> 
> What happens when src or dst or both are pointing to  odd  addresses,
> i. e. in case of unaligned accesses?

Agreed

> 
> 
> > And basically OneNAND uses the 16-bit buswidth so we don't sure the correct behavior in OneNAND
> BufferRAM if we use the char-based
> > memcpy.
> 
> I remember that ARM is terribly broken there... :-(
> 
> > Memcpy32 is 32-bytes aligned optimized. Since we know the memcpy usages in OneNAND driver, we
> guarantee the usage of memcpy32.
> 
> But the memcpy() you provide will also be used in all other partrs of
> U-Boot, won't it?
> 

If you concern the portability issues, I can omit it at this time.
How do you think about it?

Thank you,
Kyungmin Park