Messages in this thread | | | Subject | Re: [patch/rfc 2.6.25-git v2] gpio: sysfs interface | From | Ben Nizette <> | Date | Thu, 01 May 2008 09:28:13 +1000 |
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On Wed, 2008-04-30 at 14:34 -0700, David Brownell wrote: > Simple sysfs interface for GPIOs. > > /sys/class/gpio > /control ... to request a GPIO be imported or returned > /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)
You dropped the 'device' symlink? Sure it won't always be available but I did quite like the idea of being able to walk back through sysfs and discover, for example, the SPI chip select to which it's attached.
> > GPIOs may be exported by kernel code using gpio_export(), which should > be most useful for driver debugging. Userspace may also ask that they > be imported by writing to the sysfs control file, helping to cope with > incomplete board support: > > echo "23" > /sys/class/gpio/control > ... will gpio_request(23, "sysfs") and gpio_export(23); use > /sys/class/gpio/gpio-23/direction to configure it. > echo "-23" > /sys/class/gpio/control > ... will gpio_free(23) > > 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. > > 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 also needed to update > their module "owner" field ... for which missing kerneldoc was added.) > > Based on a patch from Trent Piepho <tpiepho@freescale.com>, and comments > from various folk including most recently Hartley Sweeten and Ben Nizette. > > Signed-off-by: David Brownell <dbrownell@users.sourceforge.net> > --- > Notable updates from previous version: doc update, mutex protection > for sysfs access, export basic gpio_chip info ("what GPIOs exist"), > depend on new sysfs_streq() call, simplified control file syntax. > [...] > + > +/* > + * /sys/class/gpio/control ... write-only > + * integer N: non-negative == export; negative == unexport > + */ > +static ssize_t control_store(struct class *class, const char *buf, size_t len) > +{ > + long gpio; > + int status; > + > + status = strict_strtol(buf, 0, &gpio); > + if (status < 0) > + goto done; > + > + /* No extra locking here; FLAG_SYSFS just signifies that the > + * request and export were done by on behalf of userspace, so > + * they may be undone on its behalf too. > + */ > + > + if (gpio >= 0) { /* export */ > + status = gpio_request(gpio, "sysfs"); > + if (status < 0) > + goto done; > + > + status = gpio_export(gpio); > + if (status < 0) > + gpio_free(gpio); > + else > + set_bit(FLAG_SYSFS, &gpio_desc[gpio].flags); > + > + } else { /* unexport */
Unexport gpio 0?
> + gpio = -gpio; > + > + /* reject bogus commands (gpio_unexport ignores them) */ > + if (!gpio_is_valid(gpio)) > + goto fail; > + if (!test_and_clear_bit(FLAG_SYSFS, &gpio_desc[gpio].flags)) > + goto fail; > + status = 0; > + gpio_free(gpio); > + } > +done: > + if (status) > + pr_debug("%s: status %d\n", __func__, status); > + return status ? : len; > +fail: > + pr_debug("%s: fail\n", __func__); > + return -EINVAL; > +} > +
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