From: Gilles BULOZ <gilles.buloz@kontron.com>
To: Bartosz Golaszewski <brgl@bgdev.pl>
Cc: linux-gpio@vger.kernel.org
Subject: [questions] : gpiolib and gpioset behaviour
Date: Mon, 22 Apr 2024 14:44:18 +0200 [thread overview]
Message-ID: <a6492fca-e5f9-3f5c-6a61-d08c051f0ac9@kontron.com> (raw)
Hi Bartosz,
Several years after our discussions about GPIOs, some things are still unclear
to me.
1 - The gpioset command has this in its help : "Note: the state of a GPIO line
controlled over the character device reverts to default when the last process
referencing the file descriptor representing the device file exits. This means
that it's wrong to run gpioset, have it exit and expect the line to continue
being driven high or low. It may happen if given pin is floating but it must
be interpreted as undefined behavior." But up to now I've never seen such
behaviour and I'm glad to have the GPIO set by gpioset keep their state once
the command exits. Is reverting to default an optional behaviour in the GPIO
chip driver, or in the gpiolib stack ?
2 - I've recently wrote a GPIO driver for an I2C FPGA design having ~112 GPIOs
and wanted to use get_multiple() and set_multiple to have more efficent
accesses, but realized that the line number was limited to 63 because of the
unsigned long mask/bits. But I've noticed that working on a line number >= 64
was unexpectedly calling these methods with a mask at 0 instead of calling
get/set methods, and that the only way to have things working was to not
define get_multiple/set_multiple but only get/set. Is it the expected
behaviour ?
At the end I've split the GPIOs into two banks (first with 64 and second with
48 GPIOs) to be able to use get_multiple/set_multiple.
3 - Is there some way to request a GPIO already owned by another process as
input or output, just to get the current level on the input or the level
driven on output ? This would be much more efficient for real-time
applications than asking the owner such information.
Thanks very much for your help.
Gilles Buloz
Kontron Modular Computers
next reply other threads:[~2024-04-22 12:44 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-22 12:44 Gilles BULOZ [this message]
2024-04-22 15:55 ` [questions] : gpiolib and gpioset behaviour Bartosz Golaszewski
2024-04-22 16:49 ` Gilles BULOZ
2024-04-22 18:04 ` Bartosz Golaszewski
2024-04-26 2:07 ` Kent Gibson
2024-04-26 13:08 ` Gilles BULOZ
2024-04-26 13:37 ` Kent Gibson
2024-04-26 16:16 ` Gilles BULOZ
2024-04-27 0:23 ` Kent Gibson
2024-04-27 12:09 ` Kent Gibson
2024-04-29 8:50 ` Gilles BULOZ
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