[U-Boot] [PATCH 01/10] mx27: basic cpu support

[Scott Wood]

On Mon, May 18, 2009 at 06:59:18PM +0200, Magnus Lilja wrote:
> After having browsed some powerpc code I can find two different ways
> the struct-thing is used:
> Variant A, all members declared volatile:
> struct controller_reg {
>   volatile uint32_t reg1;
>   volatile uint32_t reg2;
> }
> 
> struct controller_reg *controller = 0xCAFE0000;
> 
> Or variant B:
> struct controller_reg {
>   uint32_t reg1;
>   uint32_t reg2;
> }
> 
> volatile struct controller_reg *controller = 0xCAFE0000;

Those are both deprecated.  There should be no volatile, and you should
use I/O accessors instead.

> Also, is it OK to access the registers using reg = controller->reg1 or
> should we use reg = readl(&controller->reg1)?

The latter.  Note that readl is supposed to be little-endian regardless
of host endianness, though ARM's io.h looks a bit weird (there are
multiple definitions of readl protected by ifdefs, and the normal one
does no swapping -- and __mem_pci looks like it would result in a name
conflict).  On powerpc we have accessors with explicit endianness.

-Scott