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Date: Sat, 1 Nov 2014 16:03:00 +0900
From: Alexandre Courbot <acourbot@...dia.com>
To: Linus Walleij <linus.walleij@...aro.org>
Cc: linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
Alexandre Courbot <acourbot@...dia.com>
Subject: [RFC] gpio: remove gpio_descs global array
Replace the ARCH_NR_GPIOS-sized static array of GPIO descriptors by
dynamically-allocated arrays for each GPIO chip.
This change makes gpio_to_desc() perform in O(n) (where n is the number
of GPIO chips registered) instead of O(1), however since n is rarely
bigger than 1 or 2 no noticeable performance issue should be expected.
Besides this provides more incentive for GPIO consumers to move to the
gpiod interface. One could use a O(log(n)) structure to link the GPIO
chips together, but considering the low limit of n the hypothetical
performance benefit is probably not worth the added complexity.
The issue with this patch is its use of kzalloc() in gpiochip_add(), a
function potentially called during early boot, before kzalloc() becomes
usable. Hence its [RFC] status until we can find a solution for this or
agree that this issue is actually never ran into (from which point can
one use kzalloc()?)
While writing this I noticed a couple of weird things done in
gpiochip_add()/gpiochip_remove() and I suspect other people will find
them as well, but for now I'd like to focus on the kzalloc() issue and
see if we can push this forward. :)
Signed-off-by: Alexandre Courbot <acourbot@...dia.com>
---
drivers/gpio/gpiolib.c | 48 +++++++++++++++++++++++++++++++++---------------
1 file changed, 33 insertions(+), 15 deletions(-)
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 50e18a4..013e01e 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -47,8 +47,6 @@
*/
DEFINE_SPINLOCK(gpio_lock);
-static struct gpio_desc gpio_desc[ARCH_NR_GPIOS];
-
#define GPIO_OFFSET_VALID(chip, offset) (offset >= 0 && offset < chip->ngpio)
static DEFINE_MUTEX(gpio_lookup_lock);
@@ -65,10 +63,23 @@ static inline void desc_set_label(struct gpio_desc *d, const char *label)
*/
struct gpio_desc *gpio_to_desc(unsigned gpio)
{
- if (WARN(!gpio_is_valid(gpio), "invalid GPIO %d\n", gpio))
- return NULL;
- else
- return &gpio_desc[gpio];
+ struct gpio_chip *chip;
+ unsigned long flags;
+
+ spin_lock_irqsave(&gpio_lock, flags);
+
+ list_for_each_entry(chip, &gpio_chips, list) {
+ if (chip->base <= gpio && chip->base + chip->ngpio > gpio) {
+ spin_unlock_irqrestore(&gpio_lock, flags);
+ return &chip->desc[gpio - chip->base];
+ }
+ }
+
+ spin_unlock_irqrestore(&gpio_lock, flags);
+
+ pr_warn("invalid GPIO %d\n", gpio);
+ dump_stack();
+ return NULL;
}
EXPORT_SYMBOL_GPL(gpio_to_desc);
@@ -91,7 +102,7 @@ struct gpio_desc *gpiochip_get_desc(struct gpio_chip *chip,
*/
int desc_to_gpio(const struct gpio_desc *desc)
{
- return desc - &gpio_desc[0];
+ return desc->chip->base + (desc - &desc->chip->desc[0]);
}
EXPORT_SYMBOL_GPL(desc_to_gpio);
@@ -226,12 +237,13 @@ int gpiochip_add(struct gpio_chip *chip)
int status = 0;
unsigned id;
int base = chip->base;
+ struct gpio_desc *descs;
- if ((!gpio_is_valid(base) || !gpio_is_valid(base + chip->ngpio - 1))
- && base >= 0) {
- status = -EINVAL;
- goto fail;
- }
+ /* TODO context is potentially before kmalloc will work - how can we */
+ /* workaround this? */
+ descs = kzalloc(sizeof(descs[0] * chip->ngpio, GFP_KERNEL);
+ if (!descs)
+ return -ENOMEM;
spin_lock_irqsave(&gpio_lock, flags);
@@ -247,10 +259,8 @@ int gpiochip_add(struct gpio_chip *chip)
status = gpiochip_add_to_list(chip);
if (status == 0) {
- chip->desc = &gpio_desc[chip->base];
-
for (id = 0; id < chip->ngpio; id++) {
- struct gpio_desc *desc = &chip->desc[id];
+ struct gpio_desc *desc = &descs[id];
desc->chip = chip;
/* REVISIT: most hardware initializes GPIOs as
@@ -266,6 +276,8 @@ int gpiochip_add(struct gpio_chip *chip)
}
}
+ chip->desc = descs;
+
spin_unlock_irqrestore(&gpio_lock, flags);
#ifdef CONFIG_PINCTRL
@@ -291,6 +303,9 @@ int gpiochip_add(struct gpio_chip *chip)
unlock:
spin_unlock_irqrestore(&gpio_lock, flags);
fail:
+ chip->desc = NULL;
+ kfree(descs);
+
/* failures here can mean systems won't boot... */
pr_err("%s: GPIOs %d..%d (%s) failed to register\n", __func__,
chip->base, chip->base + chip->ngpio - 1,
@@ -331,6 +346,9 @@ void gpiochip_remove(struct gpio_chip *chip)
list_del(&chip->list);
spin_unlock_irqrestore(&gpio_lock, flags);
gpiochip_unexport(chip);
+
+ kfree(chip->desc);
+ chip->descs = NULL;
}
EXPORT_SYMBOL_GPL(gpiochip_remove);
--
2.1.3
--
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