Re: [PATCH 1 of 3] Introduce __memcpy_toio32

[Geert Uytterhoeven <geert@linux-m68k.org>]

On Tue, 27 Dec 2005, Matt Mackall wrote:
> On Tue, Dec 27, 2005 at 03:41:55PM -0800, Bryan O'Sullivan wrote:
> >  /* Create a virtual mapping cookie for an IO port range */
> >  extern void __iomem *ioport_map(unsigned long port, unsigned int nr);
> >  extern void ioport_unmap(void __iomem *);
> > diff -r 789a24638663 -r 7b7b442a4d63 lib/iomap.c
> > --- a/lib/iomap.c	Tue Dec 27 09:27:10 2005 +0800
> > +++ b/lib/iomap.c	Tue Dec 27 15:41:48 2005 -0800
> > @@ -187,6 +187,22 @@
> >  EXPORT_SYMBOL(iowrite16_rep);
> >  EXPORT_SYMBOL(iowrite32_rep);
> >  
> > +/*
> > + * Copy data to an MMIO region.  MMIO space accesses are performed
> > + * in the sizes indicated in each function's name.
> > + */
> > +void fastcall __memcpy_toio32(volatile void __iomem *d, const void *s, size_t count)
> > +{
> > +	volatile u32 __iomem *dst = d;
> > +	const u32 *src = s;
> > +
> > +	while (--count >= 0) {
> > +		__raw_writel(*src++, dst++);
> > +}
> 
> Suspicious use of volatile - writel is doing the actual write, this
> function never does a dereference. As you've already got private
> copies of the pointers already in s and d, it's perfectily reasonable
> and idiomatic to do:
> 
> 	while (--count >= 0)
> 		__raw_writel(*s++, d++);
> 
> I'd personally write this as:
> 
> 	while (count--)
> 		__raw_writel(*s++, d++);

Indeed.

BTW, does the original loop really work? Size size_t is unsigned, >= 0 is
always true and we have a nice infinite loop?

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds
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