Re: [PATCH 0/6] GPIO character device skeleton

[Johan Hovold <johan@kernel.org>]

On Fri, Oct 30, 2015 at 03:40:50PM +0100, Linus Walleij wrote:
> On Sat, Oct 24, 2015 at 7:53 PM, Markus Pargmann <mpa@pengutronix.de> wrote:
> 
> >> How to identify and manipulate individual GPIO lines from this
> >> ABI is a *LATER* *QUESTION*, this is the bare essentials for
> >> getting there: basic operations on the gpiochip device level.
> >
> > Does this include identifying GPIO lines independent of gpiochips? I
> > think that is a use-case as well.
> 
> My view is that we will NOT support any such GPIO lines.
> 
> The new API requires that everyone use gpiolib properly for all their
> GPIOs if they want to use them from userspace.
> 
> We have cases with gpiochips with a single GPIO line, so I don't
> see why we can't require that.

I think Markus question was how to *identify* lines independent of
gpiochips. That is given a line name how do we find the corresponding
chip and line (number)?

I know this series does not add such mechanisms, but we need to discuss
this from the start. Do we want user space to iterate over all gpio
chips to search for a line name? Note that this could result in more
than one gpio (chip + offset) being returned (consider hot-pluggable
devices or just dtsi).

Johan