GPIO offsets used by userspace

[Joel Stanley]

On Mon, Jan 30, 2017 at 12:04 PM, Andrew Jeffery <andrew at aj.id.au> wrote:
> Hi all,
>
> Just a heads up that when the linked patch is pulled into the OpenBMC
> kernel it will break our userspace. We will need to synchronise the
> kernel bump with the fixes for the machine configs to update the magic
> GPIO offset number.
>
> https://lkml.org/lkml/2017/1/26/786
>
> The magic offset is essentially 512-(ngpios) (I don't know why, but
> that's the behaviour), and this now varies between AST2400 and AST2500
> systems due to the AST2500 having an extra bank, and also because the
> AST2400 has a "hole" at the end of its GPIO number space.

Can you suggest a way to detect this from userspace?

Would using the chardev api make this easier?

Cheers,

Joel