Re: [Patch v3 1/2] gpio: add GPIO hogging mechanism

From: Alexandre Courbot
Date: Wed Dec 10 2014 - 06:20:21 EST

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On Fri, Dec 5, 2014 at 6:02 AM, Benoit Parrot <bparrot@xxxxxx> wrote:
> Based on Boris Brezillion's work this is a reworked patch
> of his initial GPIO hogging mechanism.
> This patch provides a way to initally configure specific GPIO
> when the gpio controller is probed.
>
> The actual DT scanning to collect the GPIO specific data is performed
> as part of the gpiochip_add().
>
> The purpose of this is to allows specific GPIOs to be configured
> without any driver specific code.
> This particularly useful because board design are getting
> increasingly complex and given SoC pins can now have upward
> of 10 mux values a lot of connections are now dependent on
> external IO muxes to switch various modes and combination.
>
> Specific drivers should not necessarily need to be aware of
> what accounts to a specific board implementation. This board level
> "description" should be best kept as part of the dts file.
>
> Signed-off-by: Benoit Parrot <bparrot@xxxxxx>
> ---
> Changes since v2:
> * Refactor the gpio-hog mechanism to split the DT related action
> from the actual "hogging" operation.
> * This allows non-DT providers to implement hogs as well.
> * Added FLAG_IS_HOGGED to mark hogged gpio and make gpiochip removal
> able to release hogged gpio.
> * Similarly to the hogging, the cleanup is performed as part of
> of_gpiochip_remove
> * Refactor the gpio-hog mechanism as private functions meant to
> be to invoked from of_gpiochip_add().
>
> Changes since v1:
> * Refactor the gpio-hog mechanism as private functions meant to
> be to invoked from of_gpiochip_add().
>
> drivers/gpio/gpiolib-of.c | 127 ++++++++++++++++++++++++++++++++++++++++++
> drivers/gpio/gpiolib.c | 118 ++++++++++++++++++++++++++++++---------
> drivers/gpio/gpiolib.h | 1 +
> include/linux/gpio/consumer.h | 9 +++
> 4 files changed, 229 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib-of.c b/drivers/gpio/gpiolib-of.c
> index 604dbe6..e13134d 100644
> --- a/drivers/gpio/gpiolib-of.c
> +++ b/drivers/gpio/gpiolib-of.c
> @@ -22,6 +22,7 @@
> #include <linux/of_gpio.h>
> #include <linux/pinctrl/pinctrl.h>
> #include <linux/slab.h>
> +#include <linux/gpio/machine.h>
>
> #include "gpiolib.h"
>
> @@ -111,6 +112,128 @@ int of_get_named_gpio_flags(struct device_node *np, const char *list_name,
> EXPORT_SYMBOL(of_get_named_gpio_flags);
>
> /**
> + * of_get_gpio_hog() - Get a GPIO hog descriptor, names and flags for GPIO API
> + * @np: device node to get GPIO from
> + * @name: GPIO line name
> + * @flags: a flags pointer to fill in
> + *
> + * Returns GPIO descriptor to use with Linux GPIO API, or one of the errno
> + * value on the error condition.
> + */
> +
> +static struct gpio_desc *of_get_gpio_hog(struct device_node *np,
> + const char **name,
> + enum gpio_lookup_flags *lflags,
> + enum gpiod_flags *dflags)
> +{
> + struct device_node *chip_np;
> + enum of_gpio_flags xlate_flags;
> + struct gpio_desc *desc;
> + const char *dir_val;
> + struct gg_data gg_data = {
> + .flags = &xlate_flags,
> + .out_gpio = NULL,
> + };
> + u32 tmp;
> + int i, ret;
> +
> + chip_np = np->parent;
> + if (!chip_np)
> + return ERR_PTR(-EINVAL);
> +
> + xlate_flags = 0;
> + *lflags = 0;
> + *dflags = 0;
> +
> + ret = of_property_read_u32(chip_np, "#gpio-cells", &tmp);
> + if (ret)
> + return ERR_PTR(ret);
> +
> + if (tmp > MAX_PHANDLE_ARGS)
> + return ERR_PTR(-EINVAL);
> +
> + gg_data.gpiospec.args_count = tmp;
> + gg_data.gpiospec.np = chip_np;
> + for (i = 0; i < tmp; i++) {
> + ret = of_property_read_u32_index(np, "gpios", i,
> + &gg_data.gpiospec.args[i]);
> + if (ret)
> + return ERR_PTR(ret);
> + }
> +
> + gpiochip_find(&gg_data, of_gpiochip_find_and_xlate);
> + if (!gg_data.out_gpio) {
> + if (np->parent == np)
> + return ERR_PTR(-ENXIO);
> + else
> + return ERR_PTR(-EPROBE_DEFER);
> + }
> +
> + if (xlate_flags & OF_GPIO_ACTIVE_LOW)
> + *lflags |= GPIO_ACTIVE_LOW;
> +
> + if (!of_property_read_string(np, "direction", &dir_val)) {
> + if (!strcmp(dir_val, "input"))
> + *dflags |= GPIOD_IN;
> + else if (!strcmp(dir_val, "output-low"))
> + *dflags |= GPIOD_OUT_LOW;
> + else if (!strcmp(dir_val, "output-high"))
> + *dflags |= GPIOD_OUT_HIGH;
> + }

... else?

We should probably return an error if the property is not specified -
is there a point in hogging a GPIO without a direction? E.g:

if (of_property_read_string(np, "direction", &dir_val))
return ERR_PTR(-EINVAL);

if (!strcmp(...

to use the nice pattern that errors (and not normal behavior) are the exception.

> +
> + if (name && of_property_read_string(np, "line-name", name))
> + *name = np->name;
> +
> + desc = gg_data.out_gpio;
> +
> + return desc;
> +}
> +
> +/**
> + * _gpiochip_hog - Scan gpio-controller and apply GPIO hog as requested
> + * @chip: gpio chip to act on
> + *
> + * This is only used by of_gpiochip_add to request/set GPIO initial
> + * configuration.
> + */
> +static void _gpiochip_hog(struct gpio_chip *chip)

Rename to of_gpio_scan_hogs() maybe?

> +{
> + struct gpio_desc *desc = NULL;
> + struct device_node *np;
> + const char *name;
> + enum gpio_lookup_flags lflags;
> + enum gpiod_flags dflags;
> +
> + for_each_child_of_node(chip->dev->of_node, np) {
> + if (!of_property_read_bool(np, "gpio-hog"))
> + continue;
> +
> + desc = of_get_gpio_hog(np, &name, &lflags, &dflags);
> + if (IS_ERR(desc))
> + continue;
> +
> + __gpiod_hog(desc, name, lflags, dflags);

You are not propagating any error returned by __gpiod_hog here.

> + }
> +}
> +
> +/**
> + * _gpiochip_unhog - Scan gpio-controller and apply GPIO hog as requested
> + * @chip: gpio chip to act on
> + *
> + * This is only used by of_gpiochip_remove to free hogged gpios
> + *
> + */
> +static void _gpiochip_unhog(struct gpio_chip *chip)
> +{
> + int id;
> +
> + for (id = 0; id < chip->ngpio; id++) {
> + if (test_bit(FLAG_IS_HOGGED, &chip->desc[id].flags))
> + gpiod_put(&chip->desc[id]);
> + }
> +}

This function is not DT-specific. It should be included in gpiolib.c
and called from there before of_gpiochip_remove().

> +
> +/**
> * of_gpio_simple_xlate - translate gpio_spec to the GPIO number and flags
> * @gc: pointer to the gpio_chip structure
> * @np: device node of the GPIO chip
> @@ -302,10 +425,14 @@ void of_gpiochip_add(struct gpio_chip *chip)
>
> of_gpiochip_add_pin_range(chip);
> of_node_get(chip->of_node);
> +
> + _gpiochip_hog(chip);
> }
>
> void of_gpiochip_remove(struct gpio_chip *chip)
> {
> gpiochip_remove_pin_ranges(chip);
> of_node_put(chip->of_node);
> +
> + _gpiochip_unhog(chip);
> }
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index e8e98ca..4ef6eb8 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -849,6 +849,7 @@ static bool __gpiod_free(struct gpio_desc *desc)
> clear_bit(FLAG_REQUESTED, &desc->flags);
> clear_bit(FLAG_OPEN_DRAIN, &desc->flags);
> clear_bit(FLAG_OPEN_SOURCE, &desc->flags);
> + clear_bit(FLAG_IS_HOGGED, &desc->flags);
> ret = true;
> }
>
> @@ -1631,6 +1632,58 @@ struct gpio_desc *__must_check __gpiod_get_optional(struct device *dev,
> }
> EXPORT_SYMBOL_GPL(__gpiod_get_optional);
>
> +
> +/**
> + * __gpiod_get_helper - helper function to request and configure a given GPIO
> + * @desc: gpio whose value will be assigned
> + * @con_id: unction within the GPIO consumer
> + * @lflags: gpio_lookup_flags - returned from of_find_gpio() or
> + * of_get_gpio_hog()
> + * @dflags: gpiod_flags - optional GPIO initialization flags
> + *
> + * Return 0 on success, -ENOENT if no GPIO has been assigned to the
> + * requested function and/or index, or another IS_ERR() code if an error
> + * occurred while trying to acquire the GPIO.
> + */
> +static int __gpiod_get_helper(struct gpio_desc *desc, const char *con_id,
> + unsigned long lflags, enum gpiod_flags dflags)
> +{
> + int status;
> +
> + status = gpiod_request(desc, con_id);

As I mentioned in the previous revision, this will prevent the module
from being unloaded with hogged GPIOs. You need to use
gpiochip_request_own_desc() here and gpiochip_free_own_desc() instead
of gpiod_put() to free hogged GPIOs. Therefore the call to
gpiod_request/gpiochip_request_own_gpio should be taken out of this
(very nice otherwise!) helper.

> +
> + if (status < 0)
> + return status;
> +
> + if (lflags & GPIO_ACTIVE_LOW)
> + set_bit(FLAG_ACTIVE_LOW, &desc->flags);
> + if (lflags & GPIO_OPEN_DRAIN)
> + set_bit(FLAG_OPEN_DRAIN, &desc->flags);
> + if (lflags & GPIO_OPEN_SOURCE)
> + set_bit(FLAG_OPEN_SOURCE, &desc->flags);
> +
> + /* No particular flag request, return here... */
> + if (!(dflags & GPIOD_FLAGS_BIT_DIR_SET)) {
> + pr_debug("no flags found for %s\n", con_id);
> + return 0;
> + }
> + /* Process flags */
> + if (dflags & GPIOD_FLAGS_BIT_DIR_OUT)
> + status = gpiod_direction_output(desc,
> + dflags & GPIOD_FLAGS_BIT_DIR_VAL);
> + else
> + status = gpiod_direction_input(desc);
> +
> + if (status < 0) {
> + pr_debug("setup of GPIO %s failed\n", con_id);
> + gpiod_put(desc);
> + return status;
> + }
> +
> + return 0;
> +}
> +
> +
> /**
> * gpiod_get_index - obtain a GPIO from a multi-index GPIO function
> * @dev: GPIO consumer, can be NULL for system-global GPIOs
> @@ -1679,35 +1732,10 @@ struct gpio_desc *__must_check __gpiod_get_index(struct device *dev,
> return desc;
> }
>
> - status = gpiod_request(desc, con_id);
> -
> + status = __gpiod_get_helper(desc, con_id, lookupflags, flags);
> if (status < 0)
> return ERR_PTR(status);
>
> - if (lookupflags & GPIO_ACTIVE_LOW)
> - set_bit(FLAG_ACTIVE_LOW, &desc->flags);
> - if (lookupflags & GPIO_OPEN_DRAIN)
> - set_bit(FLAG_OPEN_DRAIN, &desc->flags);
> - if (lookupflags & GPIO_OPEN_SOURCE)
> - set_bit(FLAG_OPEN_SOURCE, &desc->flags);
> -
> - /* No particular flag request, return here... */
> - if (!(flags & GPIOD_FLAGS_BIT_DIR_SET))
> - return desc;
> -
> - /* Process flags */
> - if (flags & GPIOD_FLAGS_BIT_DIR_OUT)
> - status = gpiod_direction_output(desc,
> - flags & GPIOD_FLAGS_BIT_DIR_VAL);
> - else
> - status = gpiod_direction_input(desc);
> -
> - if (status < 0) {
> - dev_dbg(dev, "setup of GPIO %s failed\n", con_id);
> - gpiod_put(desc);
> - return ERR_PTR(status);
> - }
> -
> return desc;
> }
> EXPORT_SYMBOL_GPL(__gpiod_get_index);
> @@ -1742,6 +1770,44 @@ struct gpio_desc *__must_check __gpiod_get_index_optional(struct device *dev,
> EXPORT_SYMBOL_GPL(__gpiod_get_index_optional);
>
> /**
> + * __gpiod_hog - Hog the specified GPIO desc given the provided flags
> + * @desc: gpio whose value will be assigned
> + * @name: gpio line name
> + * @lflags: gpio_lookup_flags - returned from of_find_gpio() or
> + * of_get_gpio_hog()
> + * @dflags: gpiod_flags - optional GPIO initialization flags
> + *
> + */
> +int __gpiod_hog(struct gpio_desc *desc, const char *name,
> + unsigned long lflags, enum gpiod_flags dflags)
> +{
> + int status;
> +
> + /* No particular flag request, not really hogging then... */
> + if (!(dflags & GPIOD_FLAGS_BIT_DIR_SET)) {
> + pr_warn("%s: GPIO:%d (%s): no hogging direction specified, bailing out\n",
> + __func__, desc_to_gpio(desc), name);
> + return -EINVAL;
> + }

Better to catch that error earlier as I suggested IMHO.

> +
> + status = __gpiod_get_helper(desc, name, lflags, dflags);
> + if (status < 0)
> + return status;
> +
> + /* Mark GPIO as hogged so it can be identified and removed later */
> + set_bit(FLAG_IS_HOGGED, &desc->flags);
> +
> + pr_debug("%s: GPIO:%d (%s) as %s%s\n", __func__,
> + desc_to_gpio(desc), name,
> + (dflags&GPIOD_FLAGS_BIT_DIR_OUT) ? "output" : "input",
> + (dflags&GPIOD_FLAGS_BIT_DIR_OUT) ?
> + (dflags&GPIOD_FLAGS_BIT_DIR_VAL) ? "/high" : "/low":"");
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(__gpiod_hog);

No export needed for this gpiolib-private function.

> +
> +/**
> * gpiod_put - dispose of a GPIO descriptor
> * @desc: GPIO descriptor to dispose of
> *
> diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
> index 9db2b6a..e3c8a1f 100644
> --- a/drivers/gpio/gpiolib.h
> +++ b/drivers/gpio/gpiolib.h
> @@ -76,6 +76,7 @@ struct gpio_desc {
> #define FLAG_OPEN_DRAIN 7 /* Gpio is open drain type */
> #define FLAG_OPEN_SOURCE 8 /* Gpio is open source type */
> #define FLAG_USED_AS_IRQ 9 /* GPIO is connected to an IRQ */
> +#define FLAG_IS_HOGGED 10 /* GPIO is hogged */
>
> #define ID_SHIFT 16 /* add new flags before this one */
>
> diff --git a/include/linux/gpio/consumer.h b/include/linux/gpio/consumer.h
> index 12f146f..626f93d 100644
> --- a/include/linux/gpio/consumer.h
> +++ b/include/linux/gpio/consumer.h
> @@ -64,6 +64,8 @@ struct gpio_desc *__must_check __devm_gpiod_get_optional(struct device *dev,
> struct gpio_desc *__must_check
> __devm_gpiod_get_index_optional(struct device *dev, const char *con_id,
> unsigned int index, enum gpiod_flags flags);
> +int __gpiod_hog(struct gpio_desc *desc, const char *name,
> + unsigned long lflags, enum gpiod_flags dflags);

Errr nope. __gpiod_hog is a gpiolib-private function, so it should be
in drivers/gpio/gpiolib.h.
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