Re: [PATCH 14/54] gpio: pch: Be sure to clamp return value

[Jean Delvare <jdelvare@suse.de>]

Hi Linus,

On Tue, 5 Jan 2016 10:46:06 +0100, Linus Walleij wrote:
> On Mon, Jan 4, 2016 at 10:41 AM, Jean Delvare <jdelvare@suse.de> wrote:
> > 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 <treding@nvidia.com>
> >> Cc: Daniel Krueger <daniel.krueger@systec-electronic.com>
> >> Cc: Jean Delvare <jdelvare@suse.de>
> >> Signed-off-by: Linus Walleij <linus.walleij@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.)
> 
> I was mainly going over and fixing all drivers with the simplest
> pattern I can think of, already merged this as it was a regression
> basically, but a patch based on my GPIO devel branch or Linux-next
> to fix it the way you want it would be
> appreciated.

Fair enough, will do.

-- 
Jean Delvare
SUSE L3 Support