[PATCH 01/13] ARM: LPC32XX: Initial architecture header files

[wellsk40@gmail.com (Kevin Wells)]

2010/2/20 Uwe Kleine-K?nig <u.kleine-koenig@pengutronix.de>
>
> Hey Kevin,
>
> > +/*
> > + * Note!
> > + * Muxed GP pins need to be setup to the GP state in the board level
> > + * code prior to using this driver.
> This is done by the imx machines, too, and I wonder if it's worth to try
> to get rid of that or at least let the gpio_direction_... functions fail
> if the pin isn't muxed as gpio. ?Thoughts?
>
HI Uwe,

In the current function of the driver, the assumption is that if an out pin
is used, it has already been muxed correctly, so requesting an output
for a pin not muxed as a GPI/O will work fine and even setting it's pin
level will work, but the level won't appear on the external pin. If
something decides to switch the mux after that state is programmed,
then the currently programmed output level will show up on that pin.

For state muxing, I would prefer to not have the GPIO driver change an
existing mux state to make a GPIO work. I don't return an error now
when a output state is used and is not muxed for an output state. But
its painless to add this.

GPI pins and GPIO pins configured as inputs always work regardless
of the muxed pin state and would never need to have a fail check, its
basically a raw pin state read.

> I didn't check the alternative functionalities for the gpios on lpc32xx,
> but what happens if any gpio is requested and the direction configured?
> Does it interfer with system functions? ?(E.g. if a pin is used in a
> dedicated say i2c function, does it make the i2c driver non-functional
> if I do gpio_direction_output(i2cpin, 1)?)
>

Setting a GPIO direction or output state will not effect a peripheral pin
(on this part) when muxed for the peripheral. (ie, setting a GPIO to output
and switching it to low when its shared with a UART pin and the mux is
setup for UART).

thanks,
Kevin

> Best regards
> Uwe
>
> --
> Pengutronix e.K. ? ? ? ? ? ? ? ? ? ? ? ? ? | Uwe Kleine-K?nig ? ? ? ? ? ?|
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