gpio: add a userspace chardev ABI for GPIOs
A new chardev that is to be used for userspace GPIO access is
added in this patch. It is intended to gradually replace the
horribly broken sysfs ABI.
Using a chardev has many upsides:
- All operations are per-gpiochip, which is the actual
device underlying the GPIOs, making us tie in to the
kernel device model properly.
- Hotpluggable GPIO controllers can come and go, as this
kind of problem has been know to userspace for character
devices since ages, and if a gpiochip handle is held in
userspace we know we will break something, whereas the
sysfs is stateless.
- The one-value-per-file rule of sysfs is really hard to
maintain when you want to twist more than one knob at a time,
for example have in-kernel APIs to switch several GPIO
lines at the same time, and this will be possible to do
with a single ioctl() from userspace, saving a lot of
context switching.
We also need to add a new bus type for GPIO. This is
necessary for example for userspace coldplug, where sysfs is
traversed to find the boot-time device nodes and create the
character devices in /dev.
This new chardev ABI is *non* *optional* and can be counted
on to be present in the future, emphasizing the preference
of this ABI.
The ABI only implements one single ioctl() to get the name
and number of GPIO lines of a chip. Even this is debatable:
see it as a minimal example for review. This ABI shall be
ruthlessly reviewed and etched in stone.
The old /sys/class/gpio is still optional to compile in,
but will be deprecated.
Unique device IDs are created using IDR, which is overkill
and insanely scalable, but also well tested.
Cc: Johan Hovold <johan@kernel.org>
Cc: Michael Welling <mwelling@ieee.org>
Cc: Markus Pargmann <mpa@pengutronix.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
2015-10-21 20:29:53 +07:00
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/*
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* <linux/gpio.h> - userspace ABI for the GPIO character devices
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*
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* Copyright (C) 2015 Linus Walleij
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*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 as published by
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* the Free Software Foundation.
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*/
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#ifndef _UAPI_GPIO_H_
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#define _UAPI_GPIO_H_
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#include <linux/ioctl.h>
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#include <linux/types.h>
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/**
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* struct gpiochip_info - Information about a certain GPIO chip
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2016-02-26 03:01:48 +07:00
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* @name: the Linux kernel name of this GPIO chip
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* @label: a functional name for this GPIO chip, such as a product
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* number, may be NULL
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gpio: add a userspace chardev ABI for GPIOs
A new chardev that is to be used for userspace GPIO access is
added in this patch. It is intended to gradually replace the
horribly broken sysfs ABI.
Using a chardev has many upsides:
- All operations are per-gpiochip, which is the actual
device underlying the GPIOs, making us tie in to the
kernel device model properly.
- Hotpluggable GPIO controllers can come and go, as this
kind of problem has been know to userspace for character
devices since ages, and if a gpiochip handle is held in
userspace we know we will break something, whereas the
sysfs is stateless.
- The one-value-per-file rule of sysfs is really hard to
maintain when you want to twist more than one knob at a time,
for example have in-kernel APIs to switch several GPIO
lines at the same time, and this will be possible to do
with a single ioctl() from userspace, saving a lot of
context switching.
We also need to add a new bus type for GPIO. This is
necessary for example for userspace coldplug, where sysfs is
traversed to find the boot-time device nodes and create the
character devices in /dev.
This new chardev ABI is *non* *optional* and can be counted
on to be present in the future, emphasizing the preference
of this ABI.
The ABI only implements one single ioctl() to get the name
and number of GPIO lines of a chip. Even this is debatable:
see it as a minimal example for review. This ABI shall be
ruthlessly reviewed and etched in stone.
The old /sys/class/gpio is still optional to compile in,
but will be deprecated.
Unique device IDs are created using IDR, which is overkill
and insanely scalable, but also well tested.
Cc: Johan Hovold <johan@kernel.org>
Cc: Michael Welling <mwelling@ieee.org>
Cc: Markus Pargmann <mpa@pengutronix.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
2015-10-21 20:29:53 +07:00
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* @lines: number of GPIO lines on this chip
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*/
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struct gpiochip_info {
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char name[32];
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2016-02-12 20:48:23 +07:00
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char label[32];
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gpio: add a userspace chardev ABI for GPIOs
A new chardev that is to be used for userspace GPIO access is
added in this patch. It is intended to gradually replace the
horribly broken sysfs ABI.
Using a chardev has many upsides:
- All operations are per-gpiochip, which is the actual
device underlying the GPIOs, making us tie in to the
kernel device model properly.
- Hotpluggable GPIO controllers can come and go, as this
kind of problem has been know to userspace for character
devices since ages, and if a gpiochip handle is held in
userspace we know we will break something, whereas the
sysfs is stateless.
- The one-value-per-file rule of sysfs is really hard to
maintain when you want to twist more than one knob at a time,
for example have in-kernel APIs to switch several GPIO
lines at the same time, and this will be possible to do
with a single ioctl() from userspace, saving a lot of
context switching.
We also need to add a new bus type for GPIO. This is
necessary for example for userspace coldplug, where sysfs is
traversed to find the boot-time device nodes and create the
character devices in /dev.
This new chardev ABI is *non* *optional* and can be counted
on to be present in the future, emphasizing the preference
of this ABI.
The ABI only implements one single ioctl() to get the name
and number of GPIO lines of a chip. Even this is debatable:
see it as a minimal example for review. This ABI shall be
ruthlessly reviewed and etched in stone.
The old /sys/class/gpio is still optional to compile in,
but will be deprecated.
Unique device IDs are created using IDR, which is overkill
and insanely scalable, but also well tested.
Cc: Johan Hovold <johan@kernel.org>
Cc: Michael Welling <mwelling@ieee.org>
Cc: Markus Pargmann <mpa@pengutronix.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
2015-10-21 20:29:53 +07:00
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__u32 lines;
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};
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2016-02-13 04:25:22 +07:00
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/* Line is in use by the kernel */
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#define GPIOLINE_FLAG_KERNEL (1UL << 0)
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#define GPIOLINE_FLAG_IS_OUT (1UL << 1)
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#define GPIOLINE_FLAG_ACTIVE_LOW (1UL << 2)
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#define GPIOLINE_FLAG_OPEN_DRAIN (1UL << 3)
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#define GPIOLINE_FLAG_OPEN_SOURCE (1UL << 4)
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/**
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* struct gpioline_info - Information about a certain GPIO line
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2016-02-26 03:01:48 +07:00
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* @line_offset: the local offset on this GPIO device, fill this in when
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* requesting the line information from the kernel
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2016-02-13 04:25:22 +07:00
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* @flags: various flags for this line
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2016-02-26 03:01:48 +07:00
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* @name: the name of this GPIO line, such as the output pin of the line on the
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* chip, a rail or a pin header name on a board, as specified by the gpio
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* chip, may be NULL
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* @consumer: a functional name for the consumer of this GPIO line as set by
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* whatever is using it, will be NULL if there is no current user but may
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* also be NULL if the consumer doesn't set this up
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2016-02-13 04:25:22 +07:00
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*/
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struct gpioline_info {
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__u32 line_offset;
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__u32 flags;
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char name[32];
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2016-02-26 03:01:48 +07:00
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char consumer[32];
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2016-02-13 04:25:22 +07:00
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};
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2016-03-10 15:48:06 +07:00
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#define GPIO_GET_CHIPINFO_IOCTL _IOR(0xB4, 0x01, struct gpiochip_info)
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#define GPIO_GET_LINEINFO_IOCTL _IOWR(0xB4, 0x02, struct gpioline_info)
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gpio: add a userspace chardev ABI for GPIOs
A new chardev that is to be used for userspace GPIO access is
added in this patch. It is intended to gradually replace the
horribly broken sysfs ABI.
Using a chardev has many upsides:
- All operations are per-gpiochip, which is the actual
device underlying the GPIOs, making us tie in to the
kernel device model properly.
- Hotpluggable GPIO controllers can come and go, as this
kind of problem has been know to userspace for character
devices since ages, and if a gpiochip handle is held in
userspace we know we will break something, whereas the
sysfs is stateless.
- The one-value-per-file rule of sysfs is really hard to
maintain when you want to twist more than one knob at a time,
for example have in-kernel APIs to switch several GPIO
lines at the same time, and this will be possible to do
with a single ioctl() from userspace, saving a lot of
context switching.
We also need to add a new bus type for GPIO. This is
necessary for example for userspace coldplug, where sysfs is
traversed to find the boot-time device nodes and create the
character devices in /dev.
This new chardev ABI is *non* *optional* and can be counted
on to be present in the future, emphasizing the preference
of this ABI.
The ABI only implements one single ioctl() to get the name
and number of GPIO lines of a chip. Even this is debatable:
see it as a minimal example for review. This ABI shall be
ruthlessly reviewed and etched in stone.
The old /sys/class/gpio is still optional to compile in,
but will be deprecated.
Unique device IDs are created using IDR, which is overkill
and insanely scalable, but also well tested.
Cc: Johan Hovold <johan@kernel.org>
Cc: Michael Welling <mwelling@ieee.org>
Cc: Markus Pargmann <mpa@pengutronix.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
2015-10-21 20:29:53 +07:00
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#endif /* _UAPI_GPIO_H_ */
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