On 03/17/2017 12:54 PM, David Rivshin wrote:

Hi Grygorii,

On Fri, 17 Mar 2017 11:45:56 -0500
Grygorii Strashko [off-list ref] wrote:

quoted

On 03/16/2017 07:57 PM, David Rivshin wrote:

quoted

From: David Rivshin <redacted>

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.  

In general this patch looks good, but there is one thing I'm worry about..

quoted

Fixes: e85ec6c3047b ("gpio: omap: fix omap2_set_gpio_debounce")
Cc: <redacted> # 4.3+
Signed-off-by: David Rivshin <redacted>
---
 drivers/gpio/gpio-omap.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/gpio/gpio-omap.c b/drivers/gpio/gpio-omap.c
index efc85a2..33ec02d 100644
--- a/drivers/gpio/gpio-omap.c
+++ b/drivers/gpio/gpio-omap.c

@@ -208,8 +208,10 @@ 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,
+static int omap2_set_gpio_debounce(struct gpio_bank *bank, unsigned offset,
 				    unsigned debounce)
 {
 	void __iomem		*reg;

@@ -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;  

This might cause boot issues as current drivers may expect this op to succeed even if
configured value is wrong - just think, may be we can do warn here and use max value as
fallback?

I have not looked through all drivers to be sure, but at least the gpio-keys 
driver requires set_debounce to return an error if it can't satisfy the request. 
In that case gpio-keys will use a software timer instead. 

                if (button->debounce_interval) {
                        error = gpiod_set_debounce(bdata->gpiod,
                                        button->debounce_interval * 1000);
                        /* use timer if gpiolib doesn't provide debounce */
                        if (error < 0)
                                bdata->software_debounce =
                                                button->debounce_interval;
                }

Also, at least some other GPIO drivers (e.g. gpio-max7760) return -EINVAL in 
such a case. And gpiolib will return -ENOTSUPP if there is no debounce 
callback at all. So I expect all drivers which use gpiod_set_debounce() to 
handle error returns gracefully. 

So I certainly understand the concern about backwards compatibility, but I 
think clipping to max is the greater of the evils in this case. Even a 
warning may be too much, because it's not necessarily anything wrong. 
Perhaps an info or debug message would be helpful, though?

If you prefer, I can try to go through all callers of gpiod_set_debounce()
and see how they'd handle an error return. The handful I've looked through so 
far all behave like gpio-keys. The only ones I'd be particularly concerned
about are platform-specific drivers which were perhaps never used with other
gpio drivers. Do you know of that I should pay special attention to?

Yeh agree. But the problem here will be not only with drivers itself - it can be wrong data in DT :(
As result, even  gpio-keys driver will just silently switch to software_debounce
without any notification.

But agree - max might not be a good choose, so can you add dev_err() below, pls. 

quoted

quoted

 	}
 
 	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 +969,15 @@ 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);

if (ret) dev_err();

quoted

quoted

 
-	return 0;
+	return ret;
 }
 
 static int omap_gpio_set_config(struct gpio_chip *chip, unsigned offset,
  

-- 
regards,
-grygorii