GPIO hint meanings

[Warner Losh]

On Sep 6, 2013, at 4:00 PM, Ian Lepore wrote:

> On Fri, 2013-09-06 at 13:42 -0600, Warner Losh wrote:
>> On Sep 6, 2013, at 12:31 PM, Luiz Otavio O Souza wrote:
>> 
>>> On 6 September 2013 14:22, Sean Bruno <sean_bruno at yahoo.com> wrote:
>>> 
>>>> I think I have a fairly firm grasp on what some of the mips/gpio hints
>>>> mean, e.g.:
>>>> 
>>>> hint.gpio.0.pinmask
>>>> hint.gpioled.0.at
>>>> hint.gpioled.0.name
>>>> hint.gpioled.0.pins
>>>> 
>>>> Fairly straightforward.
>>>> 
>>>> Now, what do these mean/do:
>>>> 
>>>> hint.gpio.0.function_set
>>>> hint.gpio.0.function_clear
>>>> 
>>>> ?
>>>> 
>>>> Sean
>>>> 
>>>> p.s. I think I'll take this and thrash together a gpioled(4) and gpio(4)
>>>> man page if I can understand better.
>>>> 
>>> 
>>> 
>>> Hi Sean,
>>> 
>>> Some of the GPIO pins on this SoC family (ar724x, ar71xx and ar9xxx) can be
>>> set between GPIO and an alternate function. So adding a pin to function_set
>>> enables this alternate function and the function_clear disables it
>>> (sometimes the bootloader doesn't initialize properly those pins).
>>> 
>>> Each SoC has its own set of pins and functions.
>>> 
>>> For ar71xx the pins 0 and 1 can be used as additional SPI chip select
>>> outputs, pins 9 and 10 are used for UART and there are also reserved pins
>>> for a SLIC/I2S interface.
>> 
>> 
>> We really need a pinmux/pinctl type interface for this which is standard across drivers/platforms.
>> 
> 
> The more ARM SoCs I look at, the less I think we could design a single
> pinmux api that works for all of them.  The number of things that can be
> controlled varies from almost-nothing to chips that let you select from
> one of a dozen different resistor strengths for pullup or pulldown per
> pin.  And that's not to mention really crazy things like daisy-chaining
> pins so the signal also goes to another pin which can be forced as an
> input even though it's normally a device output.

Linux is able to have one, although I'm not sure how they handle the daisy-chain... that's a new one on me...

Warner