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Date: Wed, 1 Jul 2009 01:25:07 -0700
From: David Brownell <david-b@...bell.net>
To: Jani Nikula <ext-jani.1.nikula@...ia.com>,
Andrew Morton <akpm@...ux-foundation.org>
Cc: akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] gpiolib: allow exported GPIO nodes to be named using sysfs links
On Wednesday 01 July 2009, Jani Nikula wrote:
> Commit 926b663ce8215ba448960e1ff6e58b67a2c3b99b (gpiolib: allow GPIOs to
> be named) already provides naming on the chip level. This patch provides
> more flexibility by allowing multiple names where ever in sysfs on a per
> GPIO basis.
>
> Adapted from David Brownell's comments on a similar concept:
> http://lkml.org/lkml/2009/4/20/203.
>
> Signed-off-by: Jani Nikula <ext-jani.1.nikula@...ia.com>
Acked-by: David Brownell <dbrownell@...rs.sourceforge.net>
Andrew, this replaces a patch now in your MM tree...
>
> ---
>
> Changes in v2:
> - remove BUG_ON()
> ---
> Documentation/gpio.txt | 10 +++++++++
> drivers/gpio/gpiolib.c | 45 ++++++++++++++++++++++++++++++++++++++++++++
> include/asm-generic/gpio.h | 8 +++++++
> include/linux/gpio.h | 9 ++++++++
> 4 files changed, 72 insertions(+), 0 deletions(-)
>
> diff --git a/Documentation/gpio.txt b/Documentation/gpio.txt
> index e4b6985..566edaa 100644
> --- a/Documentation/gpio.txt
> +++ b/Documentation/gpio.txt
> @@ -555,6 +555,11 @@ requested using gpio_request():
> /* reverse gpio_export() */
> void gpio_unexport();
>
> + /* create a sysfs link to an exported GPIO node */
> + int gpio_export_link(struct device *dev, const char *name,
> + unsigned gpio)
> +
> +
> After a kernel driver requests a GPIO, it may only be made available in
> the sysfs interface by gpio_export(). The driver can control whether the
> signal direction may change. This helps drivers prevent userspace code
> @@ -563,3 +568,8 @@ from accidentally clobbering important system state.
> This explicit exporting can help with debugging (by making some kinds
> of experiments easier), or can provide an always-there interface that's
> suitable for documenting as part of a board support package.
> +
> +After the GPIO has been exported, gpio_export_link() allows creating
> +symlinks from elsewhere in sysfs to the GPIO sysfs node. Drivers can
> +use this to provide the interface under their own device in sysfs with
> +a descriptive name.
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index 51a8d41..aef6b3d 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -505,6 +505,51 @@ static int match_export(struct device *dev, void *data)
> }
>
> /**
> + * gpio_export_link - create a sysfs link to an exported GPIO node
> + * @dev: device under which to create symlink
> + * @name: name of the symlink
> + * @gpio: gpio to create symlink to, already exported
> + *
> + * Set up a symlink from /sys/.../dev/name to /sys/class/gpio/gpioN
> + * node. Caller is responsible for unlinking.
> + *
> + * Returns zero on success, else an error.
> + */
> +int gpio_export_link(struct device *dev, const char *name, unsigned gpio)
> +{
> + struct gpio_desc *desc;
> + int status = -EINVAL;
> +
> + if (!gpio_is_valid(gpio))
> + goto done;
> +
> + mutex_lock(&sysfs_lock);
> +
> + desc = &gpio_desc[gpio];
> +
> + if (test_bit(FLAG_EXPORT, &desc->flags)) {
> + struct device *tdev;
> +
> + tdev = class_find_device(&gpio_class, NULL, desc, match_export);
> + if (tdev != NULL) {
> + status = sysfs_create_link(&dev->kobj, &tdev->kobj,
> + name);
> + } else {
> + status = -ENODEV;
> + }
> + }
> +
> + mutex_unlock(&sysfs_lock);
> +
> +done:
> + if (status)
> + pr_debug("%s: gpio%d status %d\n", __func__, gpio, status);
> +
> + return status;
> +}
> +EXPORT_SYMBOL_GPL(gpio_export_link);
> +
> +/**
> * gpio_unexport - reverse effect of gpio_export()
> * @gpio: gpio to make unavailable
> *
> diff --git a/include/asm-generic/gpio.h b/include/asm-generic/gpio.h
> index d6c379d..9cca378 100644
> --- a/include/asm-generic/gpio.h
> +++ b/include/asm-generic/gpio.h
> @@ -141,6 +141,8 @@ extern int __gpio_to_irq(unsigned gpio);
> * but more typically is configured entirely from userspace.
> */
> extern int gpio_export(unsigned gpio, bool direction_may_change);
> +extern int gpio_export_link(struct device *dev, const char *name,
> + unsigned gpio);
> extern void gpio_unexport(unsigned gpio);
>
> #endif /* CONFIG_GPIO_SYSFS */
> @@ -185,6 +187,12 @@ static inline int gpio_export(unsigned gpio, bool direction_may_change)
> return -ENOSYS;
> }
>
> +static inline int gpio_export_link(struct device *dev, const char *name,
> + unsigned gpio)
> +{
> + return -ENOSYS;
> +}
> +
> static inline void gpio_unexport(unsigned gpio)
> {
> }
> diff --git a/include/linux/gpio.h b/include/linux/gpio.h
> index e10c49a..ff374ce 100644
> --- a/include/linux/gpio.h
> +++ b/include/linux/gpio.h
> @@ -89,6 +89,15 @@ static inline int gpio_export(unsigned gpio, bool direction_may_change)
> return -EINVAL;
> }
>
> +static inline int gpio_export_link(struct device *dev, const char *name,
> + unsigned gpio)
> +{
> + /* GPIO can never have been exported */
> + WARN_ON(1);
> + return -EINVAL;
> +}
> +
> +
> static inline void gpio_unexport(unsigned gpio)
> {
> /* GPIO can never have been exported */
> --
> 1.6.3.2
>
>
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