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Date: Sun, 07 Nov 2010 19:30:33 +0100
From: Maciej Szmigiero <mhej@...pl>
To: linux-kernel@...r.kernel.org
CC: linux-arch@...r.kernel.org,
Anton Vorontsov <avorontsov@...mvista.com>,
Greg Kroah-Hartman <gregkh@...e.de>,
"Uwe Kleine-K?nig" <u.kleine-koenig@...gutronix.de>,
Grant Likely <grant.likely@...retlab.ca>,
Andrew Morton <akpm@...ux-foundation.org>,
Arnd Bergmann <arnd@...db.de>,
Jonathan Cameron <jic23@....ac.uk>,
Ben Nizette <bn@...sdigital.com>
Subject: [GPIO]implement sleeping GPIO chip removal
[GPIO]implement sleeping GPIO chip removal
Existing GPIO chip removal code is only of "non-blocking" type: if the chip is currently
requested it just returns -EBUSY.
This is bad for devices which disappear and reappear, like those on hot pluggable buses,
because it forces the driver to call gpiochip_remove() in loop until it returns 0.
This patch implements a new function which sleeps until device is free instead of
returning -EBUSY like gpiochip_remove().
Signed-off-by: Maciej Szmigiero <mhej@...pl>
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 21da9c1..a41f614 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -11,7 +11,7 @@
#include <linux/of_gpio.h>
#include <linux/idr.h>
#include <linux/slab.h>
-
+#include <linux/sched.h>
/* Optional implementation infrastructure for GPIO interfaces.
*
@@ -95,6 +95,10 @@ static int gpio_ensure_requested(struct gpio_desc *desc, unsigned offset)
const struct gpio_chip *chip = desc->chip;
const int gpio = chip->base + offset;
+ /* no new requests if chip is being deregistered */
+ if ((chip->dead) && (test_bit(FLAG_REQUESTED, &desc->flags) == 0))
+ return -ENODEV;
+
if (WARN(test_and_set_bit(FLAG_REQUESTED, &desc->flags) == 0,
"autorequest GPIO-%d\n", gpio)) {
if (!try_module_get(chip->owner)) {
@@ -1041,6 +1045,11 @@ int gpiochip_add(struct gpio_chip *chip)
goto fail;
}
+ /* make sure is not registered as already dead */
+ chip->dead = 0;
+
+ chip->removing_task = NULL;
+
spin_lock_irqsave(&gpio_lock, flags);
if (base < 0) {
@@ -1134,6 +1143,75 @@ int gpiochip_remove(struct gpio_chip *chip)
EXPORT_SYMBOL_GPL(gpiochip_remove);
/**
+ * gpiochip_remove_sleeping() - unregister a gpio_chip sleeping when needed
+ * @chip: the chip to unregister
+ * @interruptible: should the sleep be interruptible?
+ *
+ * If any of GPIOs are still requested this function will wait for them
+ * to be freed.
+ */
+int gpiochip_remove_sleeping(struct gpio_chip *chip, int interruptible)
+{
+ unsigned id;
+ unsigned long flags;
+
+ /* prevent new requests */
+ chip->dead = 1;
+
+ spin_lock_irqsave(&gpio_lock, flags);
+
+ while (1) {
+ int busy = 0;
+
+ for (id = chip->base; id < chip->base + chip->ngpio; id++) {
+ if (test_bit(FLAG_REQUESTED, &gpio_desc[id].flags)) {
+ /* printk("ID %u is still requested\n", id); */
+ busy = 1;
+ break;
+ }
+ }
+
+ if (!busy)
+ break;
+
+ set_current_state(interruptible ?
+ TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE);
+ chip->removing_task = current;
+
+ spin_unlock_irqrestore(&gpio_lock, flags);
+
+ schedule();
+
+ /* printk("GPIO remove woken up\n"); */
+
+ spin_lock_irqsave(&gpio_lock, flags);
+
+ if (interruptible && (signal_pending(current))) {
+ /* printk("GPIO remove signal pending\n"); */
+ /* mark chip alive again */
+ chip->dead = 0;
+ chip->removing_task = NULL;
+
+ spin_unlock_irqrestore(&gpio_lock, flags);
+
+ return -EINTR;
+ }
+ }
+
+ of_gpiochip_remove(chip);
+
+ for (id = chip->base; id < chip->base + chip->ngpio; id++)
+ gpio_desc[id].chip = NULL;
+
+ spin_unlock_irqrestore(&gpio_lock, flags);
+
+ gpiochip_unexport(chip);
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(gpiochip_remove_sleeping);
+
+/**
* gpiochip_find() - iterator for locating a specific gpio_chip
* @data: data to pass to match function
* @callback: Callback function to check gpio_chip
@@ -1186,6 +1264,12 @@ int gpio_request(unsigned gpio, const char *label)
if (chip == NULL)
goto done;
+ /* chip is being deregistered, prohibit new requests */
+ if (chip->dead) {
+ status = -ENODEV;
+ goto done;
+ }
+
if (!try_module_get(chip->owner))
goto done;
@@ -1254,6 +1338,9 @@ void gpio_free(unsigned gpio)
module_put(desc->chip->owner);
clear_bit(FLAG_ACTIVE_LOW, &desc->flags);
clear_bit(FLAG_REQUESTED, &desc->flags);
+
+ if (chip->removing_task != NULL)
+ wake_up_process(chip->removing_task);
} else
WARN_ON(extra_checks);
diff --git a/include/asm-generic/gpio.h b/include/asm-generic/gpio.h
index ff5c660..8576732 100644
--- a/include/asm-generic/gpio.h
+++ b/include/asm-generic/gpio.h
@@ -119,6 +119,9 @@ struct gpio_chip {
const char *const *names;
unsigned can_sleep:1;
unsigned exported:1;
+ unsigned dead:1;
+
+ struct task_struct *removing_task;
#if defined(CONFIG_OF_GPIO)
/*
@@ -139,6 +142,7 @@ extern int __must_check gpiochip_reserve(int start, int ngpio);
/* add/remove chips */
extern int gpiochip_add(struct gpio_chip *chip);
extern int __must_check gpiochip_remove(struct gpio_chip *chip);
+extern int gpiochip_remove_sleeping(struct gpio_chip *chip, int interruptible);
extern struct gpio_chip *gpiochip_find(void *data,
int (*match)(struct gpio_chip *chip,
void *data));
--
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