Re: [PATCH] powerpc: sysdev: cpm1: Optimise gpio bit calculation

[Christophe LEROY]

Le 10/03/2017 à 15:32, Segher Boessenkool a écrit :
> On Fri, Mar 10, 2017 at 03:04:48PM +0100, Christophe LEROY wrote:
> > Le 10/03/2017 à 14:06, Segher Boessenkool a écrit :
> > > On Fri, Mar 10, 2017 at 11:54:19AM +0100, Christophe LEROY wrote:
> > > > gpio_get() and gpio_set() are used extensively by some GPIO based
> > > > drivers like SPI, NAND, so it may be worth it as it doesn't impair
> > > > readability (if anyone prefers, we could write  (1 << 31) >> i  instead
> > > > of  0x80000000 >> i )
> > >
> > > 1 << 31 is undefined behaviour, of course.
> >
> > Shall it be 1U << 31 ?
>
> Sure, that works.  "1 << (31 - i)" is most readable (but it doesn't yet
> generate the code you want).

Euh .... I'm a bit lost. Do you mean the form we have today is the 
driver is wrong ?


@@ -684,9 +682,7 @@ static int cpm1_gpio32_get(struct gpio_chip *gc, 
unsigned int gpio)
 {
 	struct of_mm_gpio_chip *mm_gc = to_of_mm_gpio_chip(gc);
 	struct cpm_ioport32b __iomem *iop = mm_gc->regs;
-	u32 pin_mask;
-
-	pin_mask = 1 << (31 - gpio);
+	u32 pin_mask = 0x80000000 >> gpio;

 	return !!(in_be32(&iop->dat) & pin_mask);
 }


Which I thought could also become


@@ -684,9 +682,7 @@ static int cpm1_gpio32_get(struct gpio_chip *gc, 
unsigned int gpio)
 {
 	struct of_mm_gpio_chip *mm_gc = to_of_mm_gpio_chip(gc);
 	struct cpm_ioport32b __iomem *iop = mm_gc->regs;
-	u32 pin_mask;
-
-	pin_mask = 1 << (31 - gpio);
+	u32 pin_mask = (1 << 31) >> gpio;

 	return !!(in_be32(&iop->dat) & pin_mask);
 }


Christophe