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    SubjectRe: [patch] gpiolib: fix oops in gpio_get_value_cansleep()
    On Thu, Oct 16, 2008 at 10:06:21AM -0700, David Brownell wrote:
    > On Thursday 16 October 2008, Anton Vorontsov wrote:
    > > > -     return chip->get(chip, gpio - chip->base);
    > > > +     return chip->get ? chip->get(chip, gpio - chip->base) : 0;
    > >
    > > Why don't we check the .set in the gpio_set_value? Because
    > > we must always call gpio_direction_output()?
    >
    > Yes. The output driver needs to be explicitly enabled,
    > to avoid misbehaving electic circuitry.
    >
    >
    > > It is not exactly the
    > > same we work with the input direction.. is this documented anywhere?
    >
    > In Documentation/gpio.txt since the very first versions.
    >
    > See the section on "Spinlock-Safe GPIO access", where
    > special cases for reading the value of output GPIOs are
    > desribed. Other aspects are mentioned in other spots.
    >
    > For example, open drain signals -- as used with I2C and
    > other protocols -- only drive the "low" signal level,
    > and if code wants a "high" level it's got to verify that
    > nobody else is driving that shared line to low. By
    > reading it back, even though it's configured as output.

    I see. Much thanks for the explanations.

    --
    Anton Vorontsov
    email: cbouatmailru@gmail.com
    irc://irc.freenode.net/bd2
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