Re: simple gpio driver

Hello Grant,

Grant Likely wrote:

On Wed, Aug 12, 2009 at 11:49 PM, Heiko Schocher[off-list ref] wrote:

quoted

Hello Anton,

i am trying to use the arch/powerpc/sysdev/simple_gpio.c driver,
for accessing some gpios, and found, that u8_gpio_get()
returns not only a 1 or a 0, instead it returns the real bit
position from the gpio:

gpio    return
base    value
0       0/0x01
1       0/0x02
2       0/0x04
3       0/0x08
4       0/0x10
5       0/0x20
6       0/0x40
7       0/0x80

I also use the arch/powerpc/platforms/52xx/mpc52xx_gpio.c and
mpc52xx_gpt.c drivers, they all return for a gpio just a 1 or 0,
which seems correct to me, because a gpio can have only 1 or 0
as state ... what do you think?

I think returning '1' is perhaps slightly 'better' (however you define

Yep.

that), but I don't think the caller should make any assumptions beyond
zero/non-zero.

Hmm... why? I think a gpio_pin can have as value only 0 or 1.
Ah, if you say zero versus non zero ... hmm... okay.

quoted

I solved this issue (if it is) with the following patch:

diff --git a/arch/powerpc/sysdev/simple_gpio.c b/arch/powerpc/sysdev/simple_gpio.c
index 43c4569..bb0d79c 100644
--- a/arch/powerpc/sysdev/simple_gpio.c
+++ b/arch/powerpc/sysdev/simple_gpio.c

@@ -46,7 +46,7 @@ static int u8_gpio_get(struct gpio_chip *gc, unsigned int gpio)
 {
       struct of_mm_gpio_chip *mm_gc = to_of_mm_gpio_chip(gc);

-       return in_8(mm_gc->regs) & u8_pin2mask(gpio);
+       return (in_8(mm_gc->regs) & u8_pin2mask(gpio) ? 1 : 0);

For clarity, the brackets should be just around the & operands, and
"!= 0" instead of "? 1 : 0" might result in slightly smaller code.

return (in_8(mm_gc->regs) & u8_pin2mask(gpio)) != 0;

Yep, you are right, thanks for the info.

bye
Heiko
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