How to handle GPIO differences between P8 and P9

[Patrick Williams]

On Fri, Nov 04, 2016 at 11:45:02AM -0500, Mine wrote:
> Hi All,
> 
> This mail is to discuss how to handle GPIO differences (e.g.
> functionality, IN/OUT) between different HWs.
> 
> I went into a case the P8 uses two GPIOs, but P9 does not use them: in
> skeleton/op-hostctl/control_host_obj.c:
> 
> GPIO Throttle = (GPIO){ "BMC_THROTTLE" };
> GPIO idbtn = (GPIO){ "IDBTN" };
> ...
> rc |= gpio_write(&Throttle,1);
> rc |= gpio_write(&idbtn,0);
> 
> In P9, BMC_THROTTLE is renamed to N_MODE_N, and changed to an IN GPIO;
> IDBTN is changed to IN GPIO as well.
> If we keep the above code and overriding the GPIOs, writing
> BMC_THROTTLE takes no effect, but writing to IDBTN may break the
> function of its related front panel button.
> 
> So I think we need to distinguish such cases to avoid issues.
> 
> The question is, how to change the code to support different HWs that
> have unique GPIOs?

The current GPIO names are "Barreleye-Centric" in that they are named
based on names that were on the Barreleye board.  We need to move the
GPIO structure to be "Function-Centric" instead so that it is more
generally applicable.

That is something that will probably happen over the next few months.
Joel is working on a proposal and we'll schedule some of the refactoring
work afterwards in the userspace code.

We might go the route of having dbus objects for GPIOs instead of having
direct access, similar to what I believe the current proposal is for
LEDs.  We'll have to see what Joel proposes first and then discuss it.

I would suggest for now we simply do the minimum we need to to "make P9
work".  If this means using GPIO names that continue to match Barreleye
naming schemes, rather than Witherspoon / Romulus, I think that makes
sense.  You can always keep a comment in the System.py file that names
the "real board" name.

In cases where they have different functionality, doesn't using a
different name solve that?  Having a different name means the lookup to
"BMC_THROTTLE" or "IDBTN" will fail on Witherspoon and thus this code
will no longer function, right?

-- 
Patrick Williams
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