Re: [patch] gpiolib: fix oops in gpio_get_value_cansleep()
From: Anton Vorontsov
Date: Thu Oct 16 2008 - 13:31:30 EST
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.
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