Hi Grygorii,
On Fri, 17 Mar 2017 11:45:56 -0500
Grygorii Strashko <grygorii.strashko@xxxxxx> wrote:
> On 03/16/2017 07:57 PM, David Rivshin wrote:
> > From: David Rivshin <DRivshin@xxxxxxxxxxx>
> >
> > 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..
>
> >
> > Fixes: e85ec6c3047b ("gpio: omap: fix omap2_set_gpio_debounce")
> > Cc: <stable@xxxxxxxxxxxxxxx> # 4.3+
> > Signed-off-by: David Rivshin <drivshin@xxxxxxxxxxx>
> > ---
> > 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?
>
> > }
> >
> > 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);
> >
> > - return 0;
> > + return ret;
> > }
> >
> > static int omap_gpio_set_config(struct gpio_chip *chip, unsigned offset,
> >
>