linux-kernel - GPIOLIB, GPIO_SYS and port-wide accesses

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Message-ID: <1d3f23370908131701w50f2c550r312b14b2c7f2d12c@mail.gmail.com>
Date:	Fri, 14 Aug 2009 10:01:34 +1000
From:	John Williams <john.williams@...alogix.com>
To:	Linux Kernel list <linux-kernel@...r.kernel.org>
Cc:	John Linn <John.Linn@...inx.com>,
	Stephen Neuendorffer <stephen.neuendorffer@...inx.com>,
	David DeBonis <david.debonis@...inx.com>,
	Michal Simek <michal.simek@...alogix.com>,
	Grant Likely <grant.likely@...retlab.ca>
Subject: GPIOLIB, GPIO_SYS and port-wide accesses

Hi,

As I see it the gpiolib and sysfs export insists on single bit
accesses even on gpio pins that are located on the same physical
device/port.

A couple of years ago there was mention of port-wide accesses being a
good thing:

http://lkml.indiana.edu/hypermail/linux/kernel/0608.0/0731.html
(towards the bottom)

Did anything ever come of that?

Per-bit access is pretty inflexible if you are driving a 7-segment
display or 8-LED bar display, holding lots of file descriptors open
etc, and lots of syscall overhead.

sysfs syntax like

$ echo "240-247" > export
$ echo 255 > gpio240-247/direction  (8-bit binary mask - output)
$ echo 255 > gpio240-247/value (all ones)

would be reasonably friendly, obviously the underlying gpiolib would
have to have some notion of coupled ports.

Any thoughts?

John
-- 
John Williams,
PetaLogix - Linux Solutions for a Reconfigurable World
w: www.petalogix.com  p: +61-7-30090663  f: +61-7-30090663
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