GPIO offsets used by userspace

[Andrew Jeffery]

On Tue, 2017-01-31 at 10:55 +1030, Joel Stanley wrote:
> > 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?

Not off the top of my head.

> 
> Would using the chardev api make this easier?

To a degree. I'm not sure if named gpios are exposed by the sysfs
interface, but with the chardev API you can open the devices and
request a GPIO by name. If that fails and you have multiple devices, I
guess you can try the other gpiochips.

Andrew
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 801 bytes
Desc: This is a digitally signed message part
URL: <http://lists.ozlabs.org/pipermail/openbmc/attachments/20170131/2db075c9/attachment.sig>