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Date: Wed, 8 Oct 2008 08:28:43 +0100
From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: Mike Frysinger <vapier.adi@gmail.com>
Subject: Re: [PATCH] [MTD] [NAND] GPIO NAND flash driver
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On Wed, Oct 08, 2008 at 02:20:13AM -0400, Mike Frysinger wrote:
> On Wed, Oct 8, 2008 at 02:01, Mike Rapoport wrote:
> > +/* gpio_nand_dosync()
> > + *
> > + * needed due to bus-reordering within the PXA itself (see section on
> > + * I/O ordering in PXA manual (section 2.3, p35)
> > + */
> > +static void gpio_nand_dosync(struct gpiomtd *gpiomtd)
> > +{
> > +       unsigned long tmp;
> > +
> > +       if (gpiomtd->io_sync) {
> > +               /*
> > +                * this should generate the read, followed by
> > +                * something that depends on the read
> > +                */
> > +               tmp = readl(gpiomtd->io_sync);
> > +               asm volatile("mov %1, %0\n" : "=r" (tmp) : "r" (tmp));
> > +       }
> > +}
> 
> there isnt much point in attempting to write a generic solution if
> you're just going to turn around and stick straight assembly in the
> middle of it.  why not use a real arch-generic method like a memory
> barrier.

Linux memory barriers don't cater for what's required here.  What's
required is what's there - a read from a separate region with a
dependency on that read.  Linux has no such barrier.