GPIO Centralized Control Daemon

[Brad Bishop]

Hi Patrick

On Thu, 2017-09-14 at 15:02 -0700, Patrick Venture wrote:
> I apologize if this already exists or is in the works.
> 
> I propose we create a daemon that centralizes userspace GPIO access.
> 
> From a high level, the daemon will implement interfaces to export or
> unexport GPIOs.  Each GPIO exported will exist on the dbus:
> 
> /xyz/openbmc_project/gpio/53 and implement an interface with the
> following properties:
> value, direction, active_low, etc.

Just thinking out loud...are we sure a gpio is a useful abstraction? 
If applications all just use the chardev API what is the benefit of
having a dbus object, at the cost of API complexity.

> 
> Some doubts, should the gpio name on the dbus be the relative name
> (53), should it be the system specific name (G5) or the absolute
> name?  I'm thinking the relative name and let the daemon handle
> internalizing the adjustment from relative to absolute.
> 
> I'm working on adding GPIO support within phosphor-hwmon so that I
> can access a voltage sensor that's gated by a GPIO, and I know there 

Can you elaborate on what gated means?  Is it you have to wiggle a GPIO
before the hwmon driver for this voltage sensor can actually access the
sensor hardware?


> have been conversations and implementations of this for IPMI OEM --
> and I think it could easily be centralized.
> 
> Thoughts?
> 
> Patrick