gpiolib: better rmmod infrastructure

[linux-2.6/btrfs-unstable.git] / drivers / gpio / gpiolib.c

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/irq.h>
#include <linux/spinlock.h>

#include <asm/gpio.h>


/* Optional implementation infrastructure for GPIO interfaces.
 *
 * Platforms may want to use this if they tend to use very many GPIOs
 * that aren't part of a System-On-Chip core; or across I2C/SPI/etc.
 *
 * When kernel footprint or instruction count is an issue, simpler
 * implementations may be preferred.  The GPIO programming interface
 * allows for inlining speed-critical get/set operations for common
 * cases, so that access to SOC-integrated GPIOs can sometimes cost
 * only an instruction or two per bit.
 */


/* When debugging, extend minimal trust to callers and platform code.
 * Also emit diagnostic messages that may help initial bringup, when
 * board setup or driver bugs are most common.
 *
 * Otherwise, minimize overhead in what may be bitbanging codepaths.
 */
#ifdef  DEBUG
#define extra_checks    1
#else
#define extra_checks    0
#endif

/* gpio_lock prevents conflicts during gpio_desc[] table updates.
 * While any GPIO is requested, its gpio_chip is not removable;
 * each GPIO's "requested" flag serves as a lock and refcount.
 */
static DEFINE_SPINLOCK(gpio_lock);

struct gpio_desc {
        struct gpio_chip        *chip;
        unsigned long           flags;
/* flag symbols are bit numbers */
#define FLAG_REQUESTED  0
#define FLAG_IS_OUT     1

#ifdef CONFIG_DEBUG_FS
        const char              *label;
#endif
};
static struct gpio_desc gpio_desc[ARCH_NR_GPIOS];

static inline void desc_set_label(struct gpio_desc *d, const char *label)
{
#ifdef CONFIG_DEBUG_FS
        d->label = label;
#endif
}

/* Warn when drivers omit gpio_request() calls -- legal but ill-advised
 * when setting direction, and otherwise illegal.  Until board setup code
 * and drivers use explicit requests everywhere (which won't happen when
 * those calls have no teeth) we can't avoid autorequesting.  This nag
 * message should motivate switching to explicit requests...
 */
static void gpio_ensure_requested(struct gpio_desc *desc)
{
        if (test_and_set_bit(FLAG_REQUESTED, &desc->flags) == 0) {
                pr_warning("GPIO-%d autorequested\n", (int)(desc - gpio_desc));
                desc_set_label(desc, "[auto]");
                if (!try_module_get(desc->chip->owner))
                        pr_err("GPIO-%d: module can't be gotten \n",
                                        (int)(desc - gpio_desc));
        }
}

/* caller holds gpio_lock *OR* gpio is marked as requested */
static inline struct gpio_chip *gpio_to_chip(unsigned gpio)
{
        return gpio_desc[gpio].chip;
}

/**
 * gpiochip_add() - register a gpio_chip
 * @chip: the chip to register, with chip->base initialized
 * Context: potentially before irqs or kmalloc will work
 *
 * Returns a negative errno if the chip can't be registered, such as
 * because the chip->base is invalid or already associated with a
 * different chip.  Otherwise it returns zero as a success code.
 */
int gpiochip_add(struct gpio_chip *chip)
{
        unsigned long   flags;
        int             status = 0;
        unsigned        id;

        /* NOTE chip->base negative is reserved to mean a request for
         * dynamic allocation.  We don't currently support that.
         */

        if (chip->base < 0 || (chip->base  + chip->ngpio) >= ARCH_NR_GPIOS) {
                status = -EINVAL;
                goto fail;
        }

        spin_lock_irqsave(&gpio_lock, flags);

        /* these GPIO numbers must not be managed by another gpio_chip */
        for (id = chip->base; id < chip->base + chip->ngpio; id++) {
                if (gpio_desc[id].chip != NULL) {
                        status = -EBUSY;
                        break;
                }
        }
        if (status == 0) {
                for (id = chip->base; id < chip->base + chip->ngpio; id++) {
                        gpio_desc[id].chip = chip;
                        gpio_desc[id].flags = 0;
                }
        }

        spin_unlock_irqrestore(&gpio_lock, flags);
fail:
        /* failures here can mean systems won't boot... */
        if (status)
                pr_err("gpiochip_add: gpios %d..%d (%s) not registered\n",
                        chip->base, chip->base + chip->ngpio,
                        chip->label ? : "generic");
        return status;
}
EXPORT_SYMBOL_GPL(gpiochip_add);

/**
 * gpiochip_remove() - unregister a gpio_chip
 * @chip: the chip to unregister
 *
 * A gpio_chip with any GPIOs still requested may not be removed.
 */
int gpiochip_remove(struct gpio_chip *chip)
{
        unsigned long   flags;
        int             status = 0;
        unsigned        id;

        spin_lock_irqsave(&gpio_lock, flags);

        for (id = chip->base; id < chip->base + chip->ngpio; id++) {
                if (test_bit(FLAG_REQUESTED, &gpio_desc[id].flags)) {
                        status = -EBUSY;
                        break;
                }
        }
        if (status == 0) {
                for (id = chip->base; id < chip->base + chip->ngpio; id++)
                        gpio_desc[id].chip = NULL;
        }

        spin_unlock_irqrestore(&gpio_lock, flags);
        return status;
}
EXPORT_SYMBOL_GPL(gpiochip_remove);


/* These "optional" allocation calls help prevent drivers from stomping
 * on each other, and help provide better diagnostics in debugfs.
 * They're called even less than the "set direction" calls.
 */
int gpio_request(unsigned gpio, const char *label)
{
        struct gpio_desc        *desc;
        int                     status = -EINVAL;
        unsigned long           flags;

        spin_lock_irqsave(&gpio_lock, flags);

        if (gpio >= ARCH_NR_GPIOS)
                goto done;
        desc = &gpio_desc[gpio];
        if (desc->chip == NULL)
                goto done;

        if (!try_module_get(desc->chip->owner))
                goto done;

        /* NOTE:  gpio_request() can be called in early boot,
         * before IRQs are enabled.
         */

        if (test_and_set_bit(FLAG_REQUESTED, &desc->flags) == 0) {
                desc_set_label(desc, label ? : "?");
                status = 0;
        } else {
                status = -EBUSY;
                module_put(desc->chip->owner);
        }

done:
        if (status)
                pr_debug("gpio_request: gpio-%d (%s) status %d\n",
                        gpio, label ? : "?", status);
        spin_unlock_irqrestore(&gpio_lock, flags);
        return status;
}
EXPORT_SYMBOL_GPL(gpio_request);

void gpio_free(unsigned gpio)
{
        unsigned long           flags;
        struct gpio_desc        *desc;

        if (gpio >= ARCH_NR_GPIOS) {
                WARN_ON(extra_checks);
                return;
        }

        spin_lock_irqsave(&gpio_lock, flags);

        desc = &gpio_desc[gpio];
        if (desc->chip && test_and_clear_bit(FLAG_REQUESTED, &desc->flags)) {
                desc_set_label(desc, NULL);
                module_put(desc->chip->owner);
        } else
                WARN_ON(extra_checks);

        spin_unlock_irqrestore(&gpio_lock, flags);
}
EXPORT_SYMBOL_GPL(gpio_free);


/**
 * gpiochip_is_requested - return string iff signal was requested
 * @chip: controller managing the signal
 * @offset: of signal within controller's 0..(ngpio - 1) range
 *
 * Returns NULL if the GPIO is not currently requested, else a string.
 * If debugfs support is enabled, the string returned is the label passed
 * to gpio_request(); otherwise it is a meaningless constant.
 *
 * This function is for use by GPIO controller drivers.  The label can
 * help with diagnostics, and knowing that the signal is used as a GPIO
 * can help avoid accidentally multiplexing it to another controller.
 */
const char *gpiochip_is_requested(struct gpio_chip *chip, unsigned offset)
{
        unsigned gpio = chip->base + offset;

        if (gpio >= ARCH_NR_GPIOS || gpio_desc[gpio].chip != chip)
                return NULL;
        if (test_bit(FLAG_REQUESTED, &gpio_desc[gpio].flags) == 0)
                return NULL;
#ifdef CONFIG_DEBUG_FS
        return gpio_desc[gpio].label;
#else
        return "?";
#endif
}
EXPORT_SYMBOL_GPL(gpiochip_is_requested);


/* Drivers MUST set GPIO direction before making get/set calls.  In
 * some cases this is done in early boot, before IRQs are enabled.
 *
 * As a rule these aren't called more than once (except for drivers
 * using the open-drain emulation idiom) so these are natural places
 * to accumulate extra debugging checks.  Note that we can't (yet)
 * rely on gpio_request() having been called beforehand.
 */

int gpio_direction_input(unsigned gpio)
{
        unsigned long           flags;
        struct gpio_chip        *chip;
        struct gpio_desc        *desc = &gpio_desc[gpio];
        int                     status = -EINVAL;

        spin_lock_irqsave(&gpio_lock, flags);

        if (gpio >= ARCH_NR_GPIOS)
                goto fail;
        chip = desc->chip;
        if (!chip || !chip->get || !chip->direction_input)
                goto fail;
        gpio -= chip->base;
        if (gpio >= chip->ngpio)
                goto fail;
        gpio_ensure_requested(desc);

        /* now we know the gpio is valid and chip won't vanish */

        spin_unlock_irqrestore(&gpio_lock, flags);

        might_sleep_if(extra_checks && chip->can_sleep);

        status = chip->direction_input(chip, gpio);
        if (status == 0)
                clear_bit(FLAG_IS_OUT, &desc->flags);
        return status;
fail:
        spin_unlock_irqrestore(&gpio_lock, flags);
        if (status)
                pr_debug("%s: gpio-%d status %d\n",
                        __FUNCTION__, gpio, status);
        return status;
}
EXPORT_SYMBOL_GPL(gpio_direction_input);

int gpio_direction_output(unsigned gpio, int value)
{
        unsigned long           flags;
        struct gpio_chip        *chip;
        struct gpio_desc        *desc = &gpio_desc[gpio];
        int                     status = -EINVAL;

        spin_lock_irqsave(&gpio_lock, flags);

        if (gpio >= ARCH_NR_GPIOS)
                goto fail;
        chip = desc->chip;
        if (!chip || !chip->set || !chip->direction_output)
                goto fail;
        gpio -= chip->base;
        if (gpio >= chip->ngpio)
                goto fail;
        gpio_ensure_requested(desc);

        /* now we know the gpio is valid and chip won't vanish */

        spin_unlock_irqrestore(&gpio_lock, flags);

        might_sleep_if(extra_checks && chip->can_sleep);

        status = chip->direction_output(chip, gpio, value);
        if (status == 0)
                set_bit(FLAG_IS_OUT, &desc->flags);
        return status;
fail:
        spin_unlock_irqrestore(&gpio_lock, flags);
        if (status)
                pr_debug("%s: gpio-%d status %d\n",
                        __FUNCTION__, gpio, status);
        return status;
}
EXPORT_SYMBOL_GPL(gpio_direction_output);


/* I/O calls are only valid after configuration completed; the relevant
 * "is this a valid GPIO" error checks should already have been done.
 *
 * "Get" operations are often inlinable as reading a pin value register,
 * and masking the relevant bit in that register.
 *
 * When "set" operations are inlinable, they involve writing that mask to
 * one register to set a low value, or a different register to set it high.
 * Otherwise locking is needed, so there may be little value to inlining.
 *
 *------------------------------------------------------------------------
 *
 * IMPORTANT!!!  The hot paths -- get/set value -- assume that callers
 * have requested the GPIO.  That can include implicit requesting by
 * a direction setting call.  Marking a gpio as requested locks its chip
 * in memory, guaranteeing that these table lookups need no more locking
 * and that gpiochip_remove() will fail.
 *
 * REVISIT when debugging, consider adding some instrumentation to ensure
 * that the GPIO was actually requested.
 */

/**
 * __gpio_get_value() - return a gpio's value
 * @gpio: gpio whose value will be returned
 * Context: any
 *
 * This is used directly or indirectly to implement gpio_get_value().
 * It returns the zero or nonzero value provided by the associated
 * gpio_chip.get() method; or zero if no such method is provided.
 */
int __gpio_get_value(unsigned gpio)
{
        struct gpio_chip        *chip;

        chip = gpio_to_chip(gpio);
        WARN_ON(extra_checks && chip->can_sleep);
        return chip->get ? chip->get(chip, gpio - chip->base) : 0;
}
EXPORT_SYMBOL_GPL(__gpio_get_value);

/**
 * __gpio_set_value() - assign a gpio's value
 * @gpio: gpio whose value will be assigned
 * @value: value to assign
 * Context: any
 *
 * This is used directly or indirectly to implement gpio_set_value().
 * It invokes the associated gpio_chip.set() method.
 */
void __gpio_set_value(unsigned gpio, int value)
{
        struct gpio_chip        *chip;

        chip = gpio_to_chip(gpio);
        WARN_ON(extra_checks && chip->can_sleep);
        chip->set(chip, gpio - chip->base, value);
}
EXPORT_SYMBOL_GPL(__gpio_set_value);

/**
 * __gpio_cansleep() - report whether gpio value access will sleep
 * @gpio: gpio in question
 * Context: any
 *
 * This is used directly or indirectly to implement gpio_cansleep().  It
 * returns nonzero if access reading or writing the GPIO value can sleep.
 */
int __gpio_cansleep(unsigned gpio)
{
        struct gpio_chip        *chip;

        /* only call this on GPIOs that are valid! */
        chip = gpio_to_chip(gpio);

        return chip->can_sleep;
}
EXPORT_SYMBOL_GPL(__gpio_cansleep);



/* There's no value in making it easy to inline GPIO calls that may sleep.
 * Common examples include ones connected to I2C or SPI chips.
 */

int gpio_get_value_cansleep(unsigned gpio)
{
        struct gpio_chip        *chip;

        might_sleep_if(extra_checks);
        chip = gpio_to_chip(gpio);
        return chip->get(chip, gpio - chip->base);
}
EXPORT_SYMBOL_GPL(gpio_get_value_cansleep);

void gpio_set_value_cansleep(unsigned gpio, int value)
{
        struct gpio_chip        *chip;

        might_sleep_if(extra_checks);
        chip = gpio_to_chip(gpio);
        chip->set(chip, gpio - chip->base, value);
}
EXPORT_SYMBOL_GPL(gpio_set_value_cansleep);


#ifdef CONFIG_DEBUG_FS

#include <linux/debugfs.h>
#include <linux/seq_file.h>


static void gpiolib_dbg_show(struct seq_file *s, struct gpio_chip *chip)
{
        unsigned                i;
        unsigned                gpio = chip->base;
        struct gpio_desc        *gdesc = &gpio_desc[gpio];
        int                     is_out;

        for (i = 0; i < chip->ngpio; i++, gpio++, gdesc++) {
                if (!test_bit(FLAG_REQUESTED, &gdesc->flags))
                        continue;

                is_out = test_bit(FLAG_IS_OUT, &gdesc->flags);
                seq_printf(s, " gpio-%-3d (%-12s) %s %s",
                        gpio, gdesc->label,
                        is_out ? "out" : "in ",
                        chip->get
                                ? (chip->get(chip, i) ? "hi" : "lo")
                                : "?  ");

                if (!is_out) {
                        int             irq = gpio_to_irq(gpio);
                        struct irq_desc *desc = irq_desc + irq;

                        /* This races with request_irq(), set_irq_type(),
                         * and set_irq_wake() ... but those are "rare".
                         *
                         * More significantly, trigger type flags aren't
                         * currently maintained by genirq.
                         */
                        if (irq >= 0 && desc->action) {
                                char *trigger;

                                switch (desc->status & IRQ_TYPE_SENSE_MASK) {
                                case IRQ_TYPE_NONE:
                                        trigger = "(default)";
                                        break;
                                case IRQ_TYPE_EDGE_FALLING:
                                        trigger = "edge-falling";
                                        break;
                                case IRQ_TYPE_EDGE_RISING:
                                        trigger = "edge-rising";
                                        break;
                                case IRQ_TYPE_EDGE_BOTH:
                                        trigger = "edge-both";
                                        break;
                                case IRQ_TYPE_LEVEL_HIGH:
                                        trigger = "level-high";
                                        break;
                                case IRQ_TYPE_LEVEL_LOW:
                                        trigger = "level-low";
                                        break;
                                default:
                                        trigger = "?trigger?";
                                        break;
                                }

                                seq_printf(s, " irq-%d %s%s",
                                        irq, trigger,
                                        (desc->status & IRQ_WAKEUP)
                                                ? " wakeup" : "");
                        }
                }

                seq_printf(s, "\n");
        }
}

static int gpiolib_show(struct seq_file *s, void *unused)
{
        struct gpio_chip        *chip = NULL;
        unsigned                gpio;
        int                     started = 0;

        /* REVISIT this isn't locked against gpio_chip removal ... */

        for (gpio = 0; gpio < ARCH_NR_GPIOS; gpio++) {
                if (chip == gpio_desc[gpio].chip)
                        continue;
                chip = gpio_desc[gpio].chip;
                if (!chip)
                        continue;

                seq_printf(s, "%sGPIOs %d-%d, %s%s:\n",
                                started ? "\n" : "",
                                chip->base, chip->base + chip->ngpio - 1,
                                chip->label ? : "generic",
                                chip->can_sleep ? ", can sleep" : "");
                started = 1;
                if (chip->dbg_show)
                        chip->dbg_show(s, chip);
                else
                        gpiolib_dbg_show(s, chip);
        }
        return 0;
}

static int gpiolib_open(struct inode *inode, struct file *file)
{
        return single_open(file, gpiolib_show, NULL);
}

static struct file_operations gpiolib_operations = {
        .open           = gpiolib_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = single_release,
};

static int __init gpiolib_debugfs_init(void)
{
        /* /sys/kernel/debug/gpio */
        (void) debugfs_create_file("gpio", S_IFREG | S_IRUGO,
                                NULL, NULL, &gpiolib_operations);
        return 0;
}
subsys_initcall(gpiolib_debugfs_init);

#endif  /* DEBUG_FS */