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d8f388d8dc
This adds a simple sysfs interface for GPIOs.
/sys/class/gpio
/export ... asks the kernel to export a GPIO to userspace
/unexport ... to return a GPIO to the kernel
/gpioN ... for each exported GPIO #N
/value ... always readable, writes fail for input GPIOs
/direction ... r/w as: in, out (default low); write high, low
/gpiochipN ... for each gpiochip; #N is its first GPIO
/base ... (r/o) same as N
/label ... (r/o) descriptive, not necessarily unique
/ngpio ... (r/o) number of GPIOs; numbered N .. N+(ngpio - 1)
GPIOs claimed by kernel code may be exported by its owner using a new
gpio_export() call, which should be most useful for driver debugging.
Such exports may optionally be done without a "direction" attribute.
Userspace may ask to take over a GPIO by writing to a sysfs control file,
helping to cope with incomplete board support or other "one-off"
requirements that don't merit full kernel support:
echo 23 > /sys/class/gpio/export
... will gpio_request(23, "sysfs") and gpio_export(23);
use /sys/class/gpio/gpio-23/direction to (re)configure it,
when that GPIO can be used as both input and output.
echo 23 > /sys/class/gpio/unexport
... will gpio_free(23), when it was exported as above
The extra D-space footprint is a few hundred bytes, except for the sysfs
resources associated with each exported GPIO. The additional I-space
footprint is about two thirds of the current size of gpiolib (!). Since
no /dev node creation is involved, no "udev" support is needed.
Related changes:
* This adds a device pointer to "struct gpio_chip". When GPIO
providers initialize that, sysfs gpio class devices become children of
that device instead of being "virtual" devices.
* The (few) gpio_chip providers which have such a device node have
been updated.
* Some gpio_chip drivers also needed to update their module "owner"
field ... for which missing kerneldoc was added.
* Some gpio_chips don't support input GPIOs. Those GPIOs are now
flagged appropriately when the chip is registered.
Based on previous patches, and discussion both on and off LKML.
A Documentation/ABI/testing/sysfs-gpio update is ready to submit once this
merges to mainline.
[akpm@linux-foundation.org: a few maintenance build fixes]
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: Guennadi Liakhovetski <g.liakhovetski@pengutronix.de>
Cc: Greg KH <greg@kroah.com>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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| .. | ||
| bitops | ||
| 4level-fixup.h | ||
| atomic.h | ||
| audit_change_attr.h | ||
| audit_dir_write.h | ||
| audit_read.h | ||
| audit_signal.h | ||
| audit_write.h | ||
| bitops.h | ||
| bug.h | ||
| cmpxchg-local.h | ||
| cmpxchg.h | ||
| cputime.h | ||
| device.h | ||
| div64.h | ||
| dma-mapping-broken.h | ||
| dma-mapping.h | ||
| emergency-restart.h | ||
| errno-base.h | ||
| errno.h | ||
| fcntl.h | ||
| futex.h | ||
| gpio.h | ||
| ide_iops.h | ||
| int-l64.h | ||
| int-ll64.h | ||
| ioctl.h | ||
| iomap.h | ||
| irq_regs.h | ||
| Kbuild | ||
| Kbuild.asm | ||
| kdebug.h | ||
| libata-portmap.h | ||
| local.h | ||
| memory_model.h | ||
| mm_hooks.h | ||
| mman.h | ||
| mutex-dec.h | ||
| mutex-null.h | ||
| mutex-xchg.h | ||
| page.h | ||
| pci-dma-compat.h | ||
| pci.h | ||
| percpu.h | ||
| pgtable-nopmd.h | ||
| pgtable-nopud.h | ||
| pgtable.h | ||
| poll.h | ||
| resource.h | ||
| rtc.h | ||
| sections.h | ||
| siginfo.h | ||
| signal.h | ||
| statfs.h | ||
| termios.h | ||
| tlb.h | ||
| topology.h | ||
| uaccess.h | ||
| vmlinux.lds.h | ||
| xor.h | ||