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    SubjectRe: [patch 2.6.20-rc1 1/6] GPIO core

    > +Identifying GPIOs
    > +-----------------
    > +GPIOs are identified by unsigned integers in the range 0..MAX_INT. That
    > +reserves "negative" numbers for other purposes like marking signals as
    > +"not available on this board", or indicating faults.
    > +
    > +Platforms define how they use those integers, and usually #define symbols
    > +for the GPIO lines so that board-specific setup code directly corresponds
    > +to the relevant schematics. In contrast, drivers should only use GPIO

    Perhaps these should not be integers, then?

    typedef struct { int mydata } pin_t; prevents people from looking
    inside, allows you to typecheck, and allows expansion in (unlikely) case where
    more than int is needed? ...hotpluggable gpio pins?

    > +Spinlock-Safe GPIO access
    > +-------------------------
    > +Most GPIO controllers can be accessed with memory read/write instructions.
    > +That doesn't need to sleep, and can safely be done from inside IRQ handlers.
    > +
    > +Use these calls to access such GPIOs:
    > +
    > + /* GPIO INPUT: return zero or nonzero */
    > + int gpio_get_value(unsigned gpio);
    > +
    > + /* GPIO OUTPUT */
    > + void gpio_set_value(unsigned gpio, int value);
    > +
    > +The values are boolean, zero for low, nonzero for high. When reading the
    > +value of an output pin, the value returned should be what's seen on the
    > +pin ... that won't always match the specified output value, because of
    > +issues including wire-OR and output latencies.
    > +
    > +The get/set calls have no error returns because "invalid GPIO" should have
    > +been reported earlier in gpio_set_direction(). However, note that not all
    > +platforms can read the value of output pins; those that can't should always
    > +return zero.
    > Also, these calls will be ignored for GPIOs that can't safely
    > +be accessed wihtout sleeping (see below).

    'Silently ignored' is ugly. BUG() would be okay there.

    > +Platforms that support this type of GPIO distinguish them from other GPIOs
    > +by returning nonzero from this call:
    > +
    > + int gpio_cansleep(unsigned gpio);

    This is ugly :-(. But I don't see easy way around...

    > +GPIOs mapped to IRQs
    > +--------------------
    > +GPIO numbers are unsigned integers; so are IRQ numbers. These make up
    > +two logically distinct namespaces (GPIO 0 need not use IRQ 0). You can
    > +map between them using calls like:
    > +
    > + /* map GPIO numbers to IRQ numbers */
    > + int gpio_to_irq(unsigned gpio);
    > +
    > + /* map IRQ numbers to GPIO numbers */
    > + int irq_to_gpio(unsigned irq);

    . Don't we have irq_t already?

    > +Those return either the corresponding number in the other namespace, or
    > +else a negative errno code if the mapping can't be done. (For example,
    > +some GPIOs can't used as IRQs.) It is an unchecked error to use a GPIO
    > +number that hasn't been marked as an input using gpio_set_direction(), or

    It should be valid to do irqs on outputs, if those outputs are really
    tristates (wire-or or how you call it?)?


    Thanks for all the (sleeping) penguins.
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