[PATCH v2] gpio: omap: return error if requested debounce time is not possible

[David Rivshin]

From: David Rivshin <drivs...@allworx.com>

omap_gpio_debounce() does not validate that the requested debounce
is within a range it can handle. Instead it lets the register value
wrap silently, and always returns success.

This can lead to all sorts of unexpected behavior, such as gpio_keys
asking for a too-long debounce, but getting a very short debounce in
practice.

Fix this by returning -EINVAL if the requested value does not fit into
the register field. If there is no debounce clock available at all,
return -ENOTSUPP.

Fixes: e85ec6c3047b ("gpio: omap: fix omap2_set_gpio_debounce")
Cc: <sta...@vger.kernel.org> # 4.3+
Signed-off-by: David Rivshin <drivs...@allworx.com>
---
Changes since v1 (https://lkml.org/lkml/2017/3/16/1094):
- Added dev_info() in omap_gpio_debounce() on error.

 drivers/gpio/gpio-omap.c | 23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/drivers/gpio/gpio-omap.c b/drivers/gpio/gpio-omap.c
index efc85a2..fd9bce9 100644
--- a/drivers/gpio/gpio-omap.c
+++ b/drivers/gpio/gpio-omap.c
@@ -208,9 +208,11 @@ static inline void omap_gpio_dbck_disable(struct gpio_bank 
*bank)
  * OMAP's debounce time is in 31us steps
  *   <debounce time> = (GPIO_DEBOUNCINGTIME[7:0].DEBOUNCETIME + 1) x 31
  * so we need to convert and round up to the closest unit.
+ *
+ * Return: 0 on success, negative error otherwise.
  */
-static void omap2_set_gpio_debounce(struct gpio_bank *bank, unsigned offset,
-                                   unsigned debounce)
+static int omap2_set_gpio_debounce(struct gpio_bank *bank, unsigned offset,
+                                  unsigned debounce)
 {
        void __iomem            *reg;
        u32                     val;
@@ -218,11 +220,12 @@ static void omap2_set_gpio_debounce(struct gpio_bank 
*bank, unsigned offset,
        bool                    enable = !!debounce;
 
        if (!bank->dbck_flag)
-               return;
+               return -ENOTSUPP;
 
        if (enable) {
                debounce = DIV_ROUND_UP(debounce, 31) - 1;
-               debounce &= OMAP4_GPIO_DEBOUNCINGTIME_MASK;
+               if ((debounce & OMAP4_GPIO_DEBOUNCINGTIME_MASK) != debounce)
+                       return -EINVAL;
        }
 
        l = BIT(offset);
@@ -255,6 +258,8 @@ static void omap2_set_gpio_debounce(struct gpio_bank *bank, 
unsigned offset,
                bank->context.debounce = debounce;
                bank->context.debounce_en = val;
        }
+
+       return 0;
 }
 
 /**
@@ -964,14 +969,20 @@ static int omap_gpio_debounce(struct gpio_chip *chip, 
unsigned offset,
 {
        struct gpio_bank *bank;
        unsigned long flags;
+       int ret;
 
        bank = gpiochip_get_data(chip);
 
        raw_spin_lock_irqsave(&bank->lock, flags);
-       omap2_set_gpio_debounce(bank, offset, debounce);
+       ret = omap2_set_gpio_debounce(bank, offset, debounce);
        raw_spin_unlock_irqrestore(&bank->lock, flags);
 
-       return 0;
+       if (ret)
+               dev_info(chip->parent,
+                        "Could not set line %u debounce to %u microseconds 
(%d)",
+                        offset, debounce, ret);
+
+       return ret;
 }
 
 static int omap_gpio_set_config(struct gpio_chip *chip, unsigned offset,
-- 
2.9.3

base-commit: 5a7ad1146caa895ad718a534399e38bd2ba721b7