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SubjectRe: [RFC] generic GPIO parameter API
Hi David,

On Thu, 5 Jun 2008, David Brownell wrote:

> On Monday 02 June 2008, Guennadi Liakhovetski wrote:
> > Hi,
> >
> > as far as I understand, the current GPIO API only presents very basic GPIO
> > functionality: direction and level reading and writing. Whereas many GPIO
> > controllers have many further configurable parameters: pull-ups and
> > pull-downs, drive strength, slew rate, etc.
>
> Not at all how I'd describe it. Those omitted mechanisms are part
> of pin configuration, in the same way as function multiplexing is.
> (That is, assigning a given pin for use as a GPIO, vs hooking it up
> to an I2C, MMC, SPI, LCD, I2S, or memory controller.)
>
> Those mechanisms are highly chip-specific. Far more so than simple
> boolean GPIO mechanisms. With rare exceptions, they're needed only
> in platform-specific board setup code, which is already accessing
> lots of platform-specific programming interfaces. I'm really not
> keen on having them become part of the GPIO framework. The thought
> makes me think of trying to swallow a kitchen sink; sorry ...

Thanks for the lengthy explanation with numerous examples - this is
appreciated. But I'll omit that for this reply. Just a short question so
far - how would you handle an external GPIO expander with an additional
functionality, naimly, a possibility to switch pull-ups to GPIO pins,
specifically, it defines 4 modes for a pin: out high, out low, in without
a pullup and in with a pullup. And if the user application wants to decide
at run-time which pull-ups to switch and when? It's a MAX7301 from Maxim
btw.

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer


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