Re: [Kernel] [PATCH] gpiolib: rewrite gpiochip_add_to_list

[Bamvor Jian Zhang <bamvor.zhangjian@linaro.org>]

Hi, Julien

On 01/09/2016 11:16 PM, Bamvor Zhang Jian wrote:
> Hi, Julien
>
> On 01/09/2016 06:56 AM, Julien Grossholtz wrote:
>> Hi,
>>
>> The issue is in the break condition of the list_for_each_entry_safe loop.
>> If there is a chip at the beginning it breaks even if there is another
>> one after. You should check the next chip:
>> if (chip->base > prev->base && chip->base + chip->ngpio <= next->base)
> Thanks you suggestion. It indeed fix the issue you mentioned.
> I will send the new version after I make sure there is no other corner case.
Could you do me favor to test the following patches?
It works for the following ranges: [0,31], [32,64], [-1,32], [-1, 32] and the
other test cases I wrote.

Regards

Bamvor

---
 drivers/gpio/gpiolib.c | 65 ++++++++++++++++++++++----------------------------
 1 file changed, 28 insertions(+), 37 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 3db34e7..9460f94 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -189,55 +189,46 @@ EXPORT_SYMBOL_GPL(gpiod_get_direction);
  */
 static int gpiochip_add_to_list(struct gpio_chip *chip)
 {
-	struct gpio_chip *iterator;
-	struct gpio_chip *previous = NULL;
+	struct gpio_chip *prev, *next;
 
 	if (list_empty(&gpio_chips)) {
-		list_add_tail(&chip->list, &gpio_chips);
+		/* initial entry in list */
+		list_add(&chip->list, &gpio_chips);
 		return 0;
 	}
 
-	list_for_each_entry(iterator, &gpio_chips, list) {
-		if (iterator->base >= chip->base + chip->ngpio) {
-			/*
-			 * Iterator is the first GPIO chip so there is no
-			 * previous one
-			 */
-			if (!previous) {
-				goto found;
-			} else {
-				/*
-				 * We found a valid range(means
-				 * [base, base + ngpio - 1]) between previous
-				 * and iterator chip.
-				 */
-				if (previous->base + previous->ngpio
-						<= chip->base)
-					goto found;
-			}
-		}
-		previous = iterator;
+	next = list_entry(gpio_chips.next, struct gpio_chip, list);
+	if (chip->base + chip->ngpio <= next->base) {
+		/* add before first entry */
+		list_add(&chip->list, &gpio_chips);
+		return 0;
 	}
 
-	/*
-	 * We are beyond the last chip in the list and iterator now
-	 * points to the head.
-	 * Let iterator point to the last chip in the list.
-	 */
+	prev = list_entry(gpio_chips.prev, struct gpio_chip, list);
+	if (prev->base + prev->ngpio <= chip->base) {
+		/* add behind last entry */
+		list_add_tail(&chip->list, &gpio_chips);
+		return 0;
+	}
 
-	iterator = list_last_entry(&gpio_chips, struct gpio_chip, list);
-	if (iterator->base + iterator->ngpio <= chip->base)
-		goto found;
+	list_for_each_entry_safe(prev, next, &gpio_chips, list) {
+		/* at the end of the list */
+		if (&(next->list) == &gpio_chips)
+			break;
 
-	dev_err(chip->parent,
-	       "GPIO integer space overlap, cannot add chip\n");
-	return -EBUSY;
+		/* add between prev and next */
+		if ( prev->base + prev->ngpio <= chip->base
+				&& chip->base + chip->ngpio <= next->base) {
+			list_add(&chip->list, &prev->list);
+			return 0;
+		}
+	}
 
-found:
-	list_add_tail(&chip->list, &iterator->list);
-	return 0;
+	dev_err(chip->parent, "GPIO integer space overlap, cannot add chip\n");
+	return -EBUSY;
 }
 
+
 /**
  * Convert a GPIO name to its descriptor
  */
-- 
2.1.4