[PATCH v6 01/15] ARM: mxs: Add core definitions

On Wednesday 15 December 2010, Russell King - ARM Linux wrote:

Err, no - you're not understanding its purpose.  It's used like so:

#define FOO_BASE                IOMEM(0xf0000000)

in headers, which means you can use FOO_BASE both in C code (and it'll
be correctly typed) and also use it in assembly code (where it will be
an assembly expression.)

The alternative is we end up with:

#define FOO_ASM_BASE            0xf0000000
#define FOO_C_BASE              ((void __force __iomem *)0xf0000000)

But isn't a hardwire virtual I/O address something that should be
used only very rarely?

I would assume that we only need to have the base address of the
mapping window defined somewhere and then use offsets:

#ifdef __ASSEMBLY__
#define IOMEM_BASE	0xf0000000
#else
#define IOMEM_BASE	((void __iomem *)0xf0000000)
#endif

#define FOO_BASE	IOMEM_BASE + 0x18000
#define BAR_BASE	IOMEM_BASE + 0x20000

Or worse still, we end up with stuff like:

#define FOO_BASE                0xf0000000

struct blah {
        unsigned long base;
};

unsigned int blah(struct blah *b, unsigned int reg)
{
        return readl(b->base + reg);
}

Having IOMEM(), which can be audited to only be used in header files
defining registers gets around such problems, and ensures that the C
code is written more correctly than it otherwise would be.

With the autiting, it certainly isn't that bad. One problem
I still see is that it's defined in the platform directory,
rather than somewhere in arch/arm/include/asm/, where it could
be mandated for use across all (or all new) platforms.

Introducing generic infrastructure at a platform level seems
problematic because the good parts will need to get copied
everywhere while the bad parts get stuck in obsolete platforms
forever.

	Arnd