Re: [PATCH 1/2] gpio: omap: return error if requested debounce time is not possible

[Grygorii Strashko <grygorii.strashko@ti.com>]

On 03/16/2017 07:57 PM, David Rivshin wrote:
> From: David Rivshin <DRivshin@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.

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@vger.kernel.org> # 4.3+
> Signed-off-by: David Rivshin <drivshin@allworx.com>
> ---
>  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?

>  	}
>  
>  	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,
> 

-- 
regards,
-grygorii