GPIO offsets used by userspace
nolan.hergert at intel.com
Tue Jan 31 12:23:13 AEDT 2017
From: Andrew Jeffery [mailto:andrew at aj.id.au]
Sent: Monday, January 30, 2017 5:13 PM
To: Hergert, Nolan <nolan.hergert at intel.com>; Joel Stanley <joel at jms.id.au>; Patrick Williams <patrick at stwcx.xyz>
Cc: OpenBMC <openbmc at lists.ozlabs.org>
Subject: Re: GPIO offsets used by userspace
On Tue, 2017-01-31 at 00:50 +0000, Hergert, Nolan wrote:
> 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
> https://lwn.net/Articles/533632/. Linus Walleij's talk was helpful
> for me too:
You're right, and that's what we should be aiming for if someone has the time to do the work. In the short term, we *can* just change the hacky offset numbers that already exist in the userspace to work around the problem. It's distasteful, but not worse than what we already have.
Patrick: Did you have any plans for reworking the userspace bits?
PS: please try to reply in-line rather than top-posting, that way the context of the conversation is a bit easier to track.
Glad to, thanks for the heads up.
> -----Original Message-----
> From: openbmc [mailto:openbmc-bounces+nolan.hergert=intel.com at lists.o
> zlabs.org] On Behalf Of Joel Stanley
> Sent: Monday, January 30, 2017 4:26 PM
> To: Andrew Jeffery <andrew at aj.id.au>
> Cc: OpenBMC <openbmc at lists.ozlabs.org>
> Subject: Re: GPIO offsets used by userspace
> On Mon, Jan 30, 2017 at 12:04 PM, Andrew Jeffery <andrew at aj.id.au>
> > 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?
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> openbmc at lists.ozlabs.org
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