Hi Linus,
On Tue, 22 Dec 2015 15:20:54 +0100, Linus Walleij wrote:
> As we want gpio_chip .get() calls to be able to return negative
> error codes and propagate to drivers, we need to go over all
> drivers and make sure their return values are clamped to [0,1].
> We do this by using the ret = !!(val) design pattern.
>
> Cc: Thierry Reding <tred...@nvidia.com>
> Cc: Daniel Krueger <daniel.krue...@systec-electronic.com>
> Cc: Jean Delvare <jdelv...@suse.de>
> Signed-off-by: Linus Walleij <linus.wall...@linaro.org>
> ---
> drivers/gpio/gpio-pch.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpio/gpio-pch.c b/drivers/gpio/gpio-pch.c
> index af0715f8524b..8c45b74dcf21 100644
> --- a/drivers/gpio/gpio-pch.c
> +++ b/drivers/gpio/gpio-pch.c
> @@ -127,7 +127,7 @@ static int pch_gpio_get(struct gpio_chip *gpio, unsigned
> nr)
> {
> struct pch_gpio *chip = container_of(gpio, struct pch_gpio, gpio);
>
> - return ioread32(&chip->reg->pi) & (1 << nr);
> + return !!(ioread32(&chip->reg->pi) & (1 << nr));
> }
>
> static int pch_gpio_direction_output(struct gpio_chip *gpio, unsigned nr,
I would prefer:
return (ioread32(&chip->reg->pi) >> nr) & 1;
which is faster for the same result.
At x86 assembly level, your approach requires 5 CPU instructions (mov,
shl, test, setne and movzbl), mine only 2 CPU instructions (shr and
and.)
--
Jean Delvare
SUSE L3 Support
--
To unsubscribe from this list: send the line "unsubscribe linux-gpio" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
