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    SubjectRe: [RFC 2.6.27 1/1] gpiolib: add support for batch set of pins
    On Sunday 28 December 2008, Jaya Kumar wrote:
    > I'd like to get the start/length approach out there and in-play to
    > find out if other people want to use it and how they end up using it.

    As an *implementation* constraint, I might agree ... so
    long as it's easily changed later.

    As an *interface* constraint, I don't ... interfaces are
    rarely easy to change.

    However, in terms of implementation, most gpio chips have
    primitives that work in terms of bitmasks rather than any
    kind of start/length primitive. Example:

    - To set bits in "u32 mask":
    iowrite32(mask, bank_base + SET_REG)
    - To clear bits in "u32 mask"
    iowrite32(mask, bank_base + CLR_REG)
    - To read bits in "u32 mask",
    return mask & ioread32(bank_base + VALUE_REG)

    In short, start/length looks most like a policy, of the
    "keep them out of interfaces!" flavor, than something
    appropriate for an interface. As noted above, gpio_chip
    interfaces would more naturally use masks.

    - Dave

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      Last update: 2008-12-29 21:39    [W:0.025 / U:5.188 seconds]
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