Messages in this thread | | | From | David Brownell <> | Subject | Re: question on generic gpio interface | Date | Tue, 17 Apr 2007 09:42:49 -0700 |
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On Tuesday 17 April 2007 12:04 am, Francis Moreau wrote:
> BTW, are there any plan to make gpio usable from userspace ? I don't > know if it makes sense but I saw some patches on LKML that did that.
Only the usual plan: someone who wants that feature provides a driver, which can be merged after suitable review.
For example, the gpio_keys and leds-gpio drivers already exist to expose some kinds of GPIOs ... though not specifically as GPIOs. And I've seen various drivers that package GPIOs on specific chips, mostly for _exclusive_ use by userspace (no kernel access).
In this case I'm not entirely sure how it'd work. I've seen a few drivers which let userspace peek and poke at GPIO signals -- like one for Gumstix boards -- but generalizing the model isn't simple. Sub-problems include:
- Configuring the relevant pins. Especially for SOC cases, GPIO roles are multiplexed with several others. So there are two issues: (a) the platform-specific setup of that multiplexing, plus (b) the board-specific knowledge of what pins are truly available for use as GPIOs, and not otherwise in use.
- Enumerating those GPIOs to userspace. One SOC might have just a few dozen, another might have a few hundred; and then there are all the board-specific ones, on FPGA or I2C chips etc.
- Exposing those pins to userspace. It'd be unsafe to let pins claimed by drivers be managed by userspace; the default should be that only unclaimed GPIOs can be accessed.
Those points imply part of a design that includes board-specific hooks of various kinds (maybe delegating a lot to platform code).
But nobody's yet provided code that would generalize.
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