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author | Linus Walleij <linus.walleij@linaro.org> | 2015-10-21 13:29:53 (GMT) |
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committer | Linus Walleij <linus.walleij@linaro.org> | 2016-02-09 10:09:35 (GMT) |
commit | 3c702e9987e261042a07e43460a8148be254412e (patch) | |
tree | d95bdf248a27344606cee7eb9297d892db5b429b /include | |
parent | 34ffd85d9c46cde3dc987cac82bff370a937ac4b (diff) | |
download | linux-3c702e9987e261042a07e43460a8148be254412e.tar.xz |
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>
Diffstat (limited to 'include')
-rw-r--r-- | include/uapi/linux/Kbuild | 1 | ||||
-rw-r--r-- | include/uapi/linux/gpio.h | 28 |
2 files changed, 29 insertions, 0 deletions
diff --git a/include/uapi/linux/Kbuild b/include/uapi/linux/Kbuild index ebd10e6..5c9ae6a 100644 --- a/include/uapi/linux/Kbuild +++ b/include/uapi/linux/Kbuild @@ -138,6 +138,7 @@ header-y += genetlink.h header-y += gen_stats.h header-y += gfs2_ondisk.h header-y += gigaset_dev.h +header-y += gpio.h header-y += gsmmux.h header-y += hdlcdrv.h header-y += hdlc.h diff --git a/include/uapi/linux/gpio.h b/include/uapi/linux/gpio.h new file mode 100644 index 0000000..3188a87 --- /dev/null +++ b/include/uapi/linux/gpio.h @@ -0,0 +1,28 @@ +/* + * <linux/gpio.h> - userspace ABI for the GPIO character devices + * + * Copyright (C) 2015 Linus Walleij + * + * This program is free software; you can redistribute it and/or modify it + * under the terms of the GNU General Public License version 2 as published by + * the Free Software Foundation. + */ +#ifndef _UAPI_GPIO_H_ +#define _UAPI_GPIO_H_ + +#include <linux/ioctl.h> +#include <linux/types.h> + +/** + * struct gpiochip_info - Information about a certain GPIO chip + * @name: the name of this GPIO chip + * @lines: number of GPIO lines on this chip + */ +struct gpiochip_info { + char name[32]; + __u32 lines; +}; + +#define GPIO_GET_CHIPINFO_IOCTL _IOR('o', 0x01, struct gpiochip_info) + +#endif /* _UAPI_GPIO_H_ */ |