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Date: Tue, 5 Aug 2014 10:10:15 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: linux-gpio@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
Linus Walleij <linus.walleij@...aro.org>,
Alexandre Courbot <gnurou@...il.com>,
Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH v2] gpiolib: Provide and export gpiod_export_name
On Fri, Jul 25, 2014 at 10:12:47AM -0700, Guenter Roeck wrote:
> gpiod_export_name is similar to gpiod_export, but lets the user
> determine the name used to export a gpio pin.
>
> Currently, the pin name is determined by the chip driver with
> the 'names' array in the gpio_chip data structure, or it is set
> to gpioX, where X is the pin number, if no name is provided by
> the chip driver.
>
> It is, however, desirable to be able to provide the pin name when
> exporting the pin, for example from platform code. In other words,
> it would be useful to move the naming decision from the pin provider
> to the pin consumer. The gpio-pca953x driver provides this capability
> as part of its platform data. Other drivers could be enhanced in a
> similar way; however, this is not always possible or easy to accomplish.
> For example, mfd client drivers such as gpio-ich already use platform
> data to pass information from the mfd master driver to the client driver.
> Overloading this platform data to also provide an array of gpio pin names
> would be a challenge if not impossible.
>
> The alternative to use gpiod_export_link is also not always desirable,
> since it only creates a named link to a different directory, meaning
> the named gpio pin is not available in /sys/class/gpio but only
> in some platform specific directory and thus not as generic as possible
> and/or useful.
>
> A specific example for a use case is a gpio pin which reports AC power
> loss to user space. Depending on the platform and platform variant,
> the pin can be provided by various gpio chip drivers and pin numbers.
> It would be very desirable to have a well defined location such as
> /sys/class/gpio/ac_power_loss for this pin, so user space knows where
> to find the attribute without knowledge of the underlying platform
> variant or oher hardware details.
>
> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
Any comments / feedback ?
Thanks,
Guenter
> ---
> v2: Move name creation completely into gpiod_export().
> Do not accept NULL name in gpiod_export_name().
>
> Documentation/gpio/sysfs.txt | 12 ++++++++----
> drivers/gpio/gpiolib-sysfs.c | 37 ++++++++++++++++++++++++++++---------
> include/linux/gpio/consumer.h | 9 +++++++++
> 3 files changed, 45 insertions(+), 13 deletions(-)
>
> diff --git a/Documentation/gpio/sysfs.txt b/Documentation/gpio/sysfs.txt
> index c2c3a97..e59653a 100644
> --- a/Documentation/gpio/sysfs.txt
> +++ b/Documentation/gpio/sysfs.txt
> @@ -125,7 +125,11 @@ requested using gpio_request():
> /* export the GPIO to userspace */
> int gpiod_export(struct gpio_desc *desc, bool direction_may_change);
>
> - /* reverse gpio_export() */
> + /* export named GPIO to userspace */
> + int gpiod_export_name(struct gpio_desc *desc, const char *ioname,
> + bool direction_may_change);
> +
> + /* reverse gpiod_export() / gpiod_export_name() */
> void gpiod_unexport(struct gpio_desc *desc);
>
> /* create a sysfs link to an exported GPIO node */
> @@ -136,9 +140,9 @@ requested using gpio_request():
> int gpiod_sysfs_set_active_low(struct gpio_desc *desc, int value);
>
> After a kernel driver requests a GPIO, it may only be made available in
> -the sysfs interface by gpiod_export(). The driver can control whether the
> -signal direction may change. This helps drivers prevent userspace code
> -from accidentally clobbering important system state.
> +the sysfs interface by gpiod_export() or gpiod_export_name(). The driver
> +can control whether the signal direction may change. This helps drivers
> +prevent userspace code 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
> diff --git a/drivers/gpio/gpiolib-sysfs.c b/drivers/gpio/gpiolib-sysfs.c
> index 5f2150b..0c86a0c 100644
> --- a/drivers/gpio/gpiolib-sysfs.c
> +++ b/drivers/gpio/gpiolib-sysfs.c
> @@ -523,13 +523,12 @@ static struct class gpio_class = {
> *
> * Returns zero on success, else an error.
> */
> -int gpiod_export(struct gpio_desc *desc, bool direction_may_change)
> +int gpiod_export_name(struct gpio_desc *desc, const char *ioname,
> + bool direction_may_change)
> {
> unsigned long flags;
> int status;
> - const char *ioname = NULL;
> struct device *dev;
> - int offset;
>
> /* can't export until sysfs is available ... */
> if (!gpio_class.p) {
> @@ -542,6 +541,11 @@ int gpiod_export(struct gpio_desc *desc, bool direction_may_change)
> return -EINVAL;
> }
>
> + if (!ioname) {
> + pr_debug("%s: invalid ioname\n", __func__);
> + return -EINVAL;
> + }
> +
> mutex_lock(&sysfs_lock);
>
> spin_lock_irqsave(&gpio_lock, flags);
> @@ -560,13 +564,8 @@ int gpiod_export(struct gpio_desc *desc, bool direction_may_change)
> direction_may_change = false;
> spin_unlock_irqrestore(&gpio_lock, flags);
>
> - offset = gpio_chip_hwgpio(desc);
> - if (desc->chip->names && desc->chip->names[offset])
> - ioname = desc->chip->names[offset];
> -
> dev = device_create(&gpio_class, desc->chip->dev, MKDEV(0, 0),
> - desc, ioname ? ioname : "gpio%u",
> - desc_to_gpio(desc));
> + desc, ioname, desc_to_gpio(desc));
> if (IS_ERR(dev)) {
> status = PTR_ERR(dev);
> goto fail_unlock;
> @@ -600,6 +599,26 @@ fail_unlock:
> gpiod_dbg(desc, "%s: status %d\n", __func__, status);
> return status;
> }
> +EXPORT_SYMBOL_GPL(gpiod_export_name);
> +
> +int gpiod_export(struct gpio_desc *desc, bool direction_may_change)
> +{
> + const char *ioname;
> + int offset;
> +
> + if (!desc) {
> + pr_debug("%s: invalid gpio descriptor\n", __func__);
> + return -EINVAL;
> + }
> +
> + offset = gpio_chip_hwgpio(desc);
> + if (desc->chip->names && desc->chip->names[offset])
> + ioname = desc->chip->names[offset];
> + else
> + ioname = "gpio%u";
> +
> + return gpiod_export_name(desc, ioname, direction_may_change);
> +}
> EXPORT_SYMBOL_GPL(gpiod_export);
>
> static int match_export(struct device *dev, const void *data)
> diff --git a/include/linux/gpio/consumer.h b/include/linux/gpio/consumer.h
> index 05e53cc..986da3e 100644
> --- a/include/linux/gpio/consumer.h
> +++ b/include/linux/gpio/consumer.h
> @@ -260,6 +260,8 @@ static inline int desc_to_gpio(const struct gpio_desc *desc)
> #if IS_ENABLED(CONFIG_GPIOLIB) && IS_ENABLED(CONFIG_GPIO_SYSFS)
>
> int gpiod_export(struct gpio_desc *desc, bool direction_may_change);
> +int gpiod_export_name(struct gpio_desc *desc, const char *ioname,
> + bool direction_may_change);
> int gpiod_export_link(struct device *dev, const char *name,
> struct gpio_desc *desc);
> int gpiod_sysfs_set_active_low(struct gpio_desc *desc, int value);
> @@ -273,6 +275,13 @@ static inline int gpiod_export(struct gpio_desc *desc,
> return -ENOSYS;
> }
>
> +static inline int gpiod_export_name(struct gpio_desc *desc,
> + const char *ioname,
> + bool direction_may_change)
> +{
> + return -ENOSYS;
> +}
> +
> static inline int gpiod_export_link(struct device *dev, const char *name,
> struct gpio_desc *desc)
> {
> --
> 1.9.1
>
>
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