[PATCH 1/2] gpio: add pin biasing and drive mode to gpiolib
bn at niasdigital.com
Wed Apr 20 19:32:26 EDT 2011
On 20/04/2011, at 10:21 PM, Linus Walleij wrote:
> 2011/4/19 Ben Nizette <bn at niasdigital.com>:
>> On 18/04/2011, at 10:26 PM, Alan Cox wrote:
>>> The logical extension to that is to delete the gpio layer because the
>>> board code can do it ?
>> Well anything that is done once at startup, yes,
> This patch is about biasing and drive modes. We need to alter
> these at runtime (from board code, indeed) due to the fact that
> when you go to sleep e.g. floating a pin yeilds better power
This is actually an interesting case because floating pins yeild
/worse/ power characteristics (each transistor of the push-pull
is on a little bit and you get a path straight through) . To
get good power performance you want to pull an input pin high or
low but which of those two directions depends on external
constraints, i.e. the board. This is a case where the driver
should /not/ go playing with things it can't fully understand.
Perhaps one of the properties that a board can set in a gpio chip
driver is the suspend state and have suspend/resume hooks in the
gpio chip take care of setting things up on each side.
> Linus Walleij
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