Re: Add skeleton "generic IO mapping" infrastructure.

[Jeff Garzik]

David Woodhouse wrote:
> On Mon, 2004-09-13 at 18:32 +0000, Linux Kernel Mailing List wrote:
>
> > ChangeSet 1.1869, 2004/09/13 11:32:00-07:00, torvalds@xxxxxxxxxxxxxxx
> >
> > 	Add skeleton "generic IO mapping" infrastructure.
> > 	
> > 	Jeff wants to use this to clean up SATA and some network drivers.
>
>
>
> > + * Read/write from/to an (offsettable) iomem cookie. It might be a PIO
> > + * access or a MMIO access, these functions don't care. The info is
> > + * encoded in the hardware mapping set up by the mapping functions
> > + * (or the cookie itself, depending on implementation and hw).
> > + *
> > + * The generic routines don't assume any hardware mappings, and just
> > + * encode the PIO/MMIO as part of the cookie. They coldly assume that
> > + * the MMIO IO mappings are not in the low address range.
> > + *
> > + * Architectures for which this is not true can't use this generic
> > + * implementation and should do their own copy.
> > + *
> > + * We encode the physical PIO addresses (0-0xffff) into the
> > + * pointer by offsetting them with a constant (0x10000) and
> > + * assuming that all the low addresses are always PIO. That means
> > + * we can do some sanity checks on the low bits, and don't
> > + * need to just take things for granted.
> > + */
> > +#define PIO_OFFSET	0x10000
> > +#define PIO_MASK	0x0ffff
> > +#define PIO_RESERVED	0x40000
>
>
> > +#define IO_COND(addr, is_pio, is_mmio) do {			\
> > +	unsigned long port = (unsigned long __force)addr;	\
> > +	if (port < PIO_RESERVED) {				\
> > +		VERIFY_PIO(port);				\
> > +		port &= PIO_MASK;				\
> > +		is_pio;						\
> > +	} else {						\
> > +		is_mmio;					\
> > +	}							\
> > +} while (0)
>
>
> Argh! Please no. You can't infer the IO space from the address. Provide
> a cookie containing {space, address} instead -- or indeed {bus,
> address}. Let some architectures optimise that by ignoring the bus and
> working it out from the address if you must, but don't put that in the
> generic version.

Override it in your arch if you don't like the generic version ;-)

	Jeff



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