GPIO offsets used by userspace

Hergert, Nolan nolan.hergert at
Tue Jan 31 11:50:00 AEDT 2017

Correct me if I'm wrong, but I think the maintainers are moving away from literal gpio numbers to named descriptors ("disk_led") in the device tree, as we're moving to more dynamic hardware Linus Walleij's talk was helpful  for me too: 


-----Original Message-----
From: openbmc [ at] On Behalf Of Joel Stanley
Sent: Monday, January 30, 2017 4:26 PM
To: Andrew Jeffery <andrew at>
Cc: OpenBMC <openbmc at>
Subject: Re: GPIO offsets used by userspace

On Mon, Jan 30, 2017 at 12:04 PM, Andrew Jeffery <andrew at> 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.
> 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?


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