[PATCH v2 1/5] ARM: SPMP8000: Add machine base files

[Zoltan Devai]

2011/10/22 Russell King - ARM Linux <linux at arm.linux.org.uk>:
> On Wed, Oct 19, 2011 at 09:15:35PM +0200, Arnd Bergmann wrote:
>> > +#define SERIAL_BASE        ((volatile unsigned char *)SPMP8000_UARTC0_BASE)
>>
>> drop this, then
>>
>> > +static void putc(const char c)
>> > +{
>> > +   volatile unsigned char *base = SERIAL_BASE;
>>
>> make this a "unsigned char __iomem *".
>>
>> > +   int i;
>> > +
>> > +   for (i = 0; i < 0x1000; i++) {
>> > +           if (base[UART_LSR << 2] & UART_LSR_THRE)
>> > +                   break;
>> > +           barrier();
>> > +   }
>> > +
>> > +   base[UART_TX << 2] = c;
>> > +}
>>
>> and use readb_relaxed/writeb_relaxed to do the access. You should
>> never just dereference volatile pointers to do an MMIO access.
>
> Note that uncompress.h isn't part of the kernel proper, and so the
> MMIO accessors may not work (depends whether the arch out-of-lines
> them.)  Moreover, as the MMU is setup with 1:1 mappings, arguably
> it's not IOMEM anyway.
What's the preferred method then ?
The current uncompress.h files use all possible methods.
This is certainly also a question for the uncompress.h cleanup series.

Z