GPIO offsets used by userspace

[Hergert, Nolan]

-----Original Message-----
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

Hi Nolan!

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:
> http://elinux.org/images/9/9b/GPIO_for_Engineers_and_Makers.pdf

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?

Cheers,

Andrew

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. 

> 
> Nolan
> 
> -----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>
> 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
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