On Sun, Sep 30, 2012 at 5:09 PM, Roland Stigge [off-list ref] wrote:

Hi Stijn,

On 30/09/12 16:52, Stijn Devriendt wrote:

quoted

quoted

One question: How did you solve the one-value-per-file in the sysfs
interface?

By exporting the group as a whole:
/sys/.../gpiogroup248/value
where value contains a decimal representing the group value.
Again, this respects the ordering of the pins:

Actual pins: 0x2D (b 0010 1101)
Selected pins: 6 3 0 1
Readout: 6 (b 0 1 1 0)

The export sysfs file does, however, accept multiple gpio IDs for groups.
Not sure if this is a 'violation' per se...

If I understand correctly, it's a violation (single-value should hold
for read and write).

To solve it, I have the following in mind: /sys/.../gpiogroupXXX/
contains files "bit0" ... "bit31" which contain a gpio number each,
empty if "unconnected".

Unfortunately that means you can't atomically create a group.
It also creates a mess to keep ordering intact and to either
keep the current pin state or override it at allocation-time.

Rules are rules, but why make the interface overly complex when
the multi-value file is saner, cleaner and simpler?
I know I'm on the happy/corporate side of things and I can violate
whatever rule I can if it gets our product shipping, but I'd still
propose to have the multi-value approach, even in mainline.

Regards,
Stijn