Re: [PATCH] [MTD] [NAND] GPIO NAND flash driver

Mike Frysinger
2008-10-08T07:29:59Z

On Wed, Oct 8, 2008 at 03:28, Russell King - ARM Linux wrote:
> 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.

thanks, this kind of comment in the source would be useful ... but
what is also needed is '#ifdef __arm__'
-mike