gpio: Prevent an integer overflow in the pca953x driver

Interrupts were missed if an 8-bit integer overflow occurred. This was
observed when bank0,pin7 and bank1,pin7 changed simultaniously.

As the 8-bit totals were only checked against zero, replace them with
booleans. Name the booleans so that their purpose is clear.

Signed-off-by: Joshua Scott <joshua.scott@alliedtelesis.co.nz>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

1 files changed, 12 insertions, 9 deletions

diff --git a/drivers/gpio/gpio-pca953x.c b/drivers/gpio/gpio-pca953x.c
index eed42035207d..d233eb3b8132 100644
--- a/drivers/gpio/gpio-pca953x.c
+++ b/drivers/gpio/gpio-pca953x.c
@@ -443,12 +443,13 @@ static struct irq_chip pca953x_irq_chip = {
         .irq_set_type           = pca953x_irq_set_type,
 };
 
-static u8 pca953x_irq_pending(struct pca953x_chip *chip, u8 *pending)
+static bool pca953x_irq_pending(struct pca953x_chip *chip, u8 *pending)
 {
         u8 cur_stat[MAX_BANK];
         u8 old_stat[MAX_BANK];
-        u8 pendings = 0;
-        u8 trigger[MAX_BANK], triggers = 0;
+        bool pending_seen = false;
+        bool trigger_seen = false;
+        u8 trigger[MAX_BANK];
         int ret, i, offset = 0;
 
         switch (chip->chip_type) {
@@ -461,7 +462,7 @@ static u8 pca953x_irq_pending(struct pca953x_chip *chip, u8 *pending)
         }
         ret = pca953x_read_regs(chip, offset, cur_stat);
         if (ret)
-                return 0;
+                return false;
 
         /* Remove output pins from the equation */
         for (i = 0; i < NBANK(chip); i++)
@@ -471,11 +472,12 @@ static u8 pca953x_irq_pending(struct pca953x_chip *chip, u8 *pending)
 
         for (i = 0; i < NBANK(chip); i++) {
                 trigger[i] = (cur_stat[i] ^ old_stat[i]) & chip->irq_mask[i];
-                triggers += trigger[i];
+                if (trigger[i])
+                        trigger_seen = true;
         }
 
-        if (!triggers)
-                return 0;
+        if (!trigger_seen)
+                return false;
 
         memcpy(chip->irq_stat, cur_stat, NBANK(chip));
 
@@ -483,10 +485,11 @@ static u8 pca953x_irq_pending(struct pca953x_chip *chip, u8 *pending)
                 pending[i] = (old_stat[i] & chip->irq_trig_fall[i]) |
                         (cur_stat[i] & chip->irq_trig_raise[i]);
                 pending[i] &= trigger[i];
-                pendings += pending[i];
+                if (pending[i])
+                        pending_seen = true;
         }
 
-        return pendings;
+        return pending_seen;
 }
 
 static irqreturn_t pca953x_irq_handler(int irq, void *devid)