[PATCH] arm pxa: remove "direction input" forcing for IRQ GPIOs

[Russell King - ARM Linux]

On Tue, Nov 17, 2009 at 07:02:00PM +0100, Rodolfo Giometti wrote:
> On Tue, Nov 17, 2009 at 06:11:16PM +0100, Daniel Mack wrote:
> > I'm still not convinced that driving the pad as output GPIO and then
> > applying a different level externally to generate an IRQ is intended.
> 
> No external different level applyed! Just a pull-down enabled by a
> machanical switch: if no cards are inserted I read 1 but if I insert a
> card I got 0 due the pull-down enabling.

I'm sorry, but I really can't believe you mean what you just said.  The
two sentences are definitely contradictory.

In the first, you say that you're not applying a different level.

In the second, you say that you're applying zero volts to the output.
That _is_ a different level, no two ways about it.

By doing so, you are brute-force fighting the FET in the SoC which is
trying to pull the output up to logic '1'.  God knows how much current
you're causing the FET to pass - and therefore how much power it is
dissapating - but according to the PXA270 spec, it'll be in excess of
3mA.  (At 3mA, the output voltage on a GPIO pin is guaranteed to be,
for logic 1, at least 0.8 * VCC_IO).

This is in no way good electronic practice.