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    SubjectRe: Add skeleton "generic IO mapping" infrastructure.
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    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@ppc970.osdl.org
    >
    > 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.

    --
    dwmw2


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