Subject: Re: [PATCH v2] powerpc/gpio: Fix the wrong GPIO input data on MPC8572/MPC8536

From: Liu Gang <[email-masked]>
Date: Tue, 26 Nov 2013 17:20:44 +0800

On Fri, 2013-11-22 at 14:51 -0600, Kumar Gala wrote:
> > drivers/gpio/gpio-mpc8xxx.c | 8 ++++++--
> > 1 file changed, 6 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpio/gpio-mpc8xxx.c b/drivers/gpio/gpio-mpc8xxx.c
> > index 914e859..d7d6d72 100644
> > --- a/drivers/gpio/gpio-mpc8xxx.c
> > +++ b/drivers/gpio/gpio-mpc8xxx.c
> > @@ -70,10 +70,14 @@ static int mpc8572_gpio_get(struct gpio_chip *gc, unsigned int gpio)
> > 	u32 val;
> > 	struct of_mm_gpio_chip *mm = to_of_mm_gpio_chip(gc);
> > 	struct mpc8xxx_gpio_chip *mpc8xxx_gc = to_mpc8xxx_gpio_chip(mm);
> > +	u32 out_mask, out_shadow;
> > 
> > -	val = in_be32(mm->regs + GPIO_DAT) & ~in_be32(mm->regs + GPIO_DIR);
> > +	out_mask = in_be32(mm->regs + GPIO_DIR);
> > 
> > -	return (val | mpc8xxx_gc->data) & mpc8xxx_gpio2mask(gpio);
> > +	val = in_be32(mm->regs + GPIO_DAT) & ~out_mask;
> > +	out_shadow = mpc8xxx_gc->data & out_mask;
> > +
> > +	return (val | out_shadow) & mpc8xxx_gpio2mask(gpio);
> > }
> 
> I really think a comment is worth adding here about why we do this.
> 
> - k

Hi, Kumar,
Thanks for your comment. In fact, there already had some comments above
the function:

/* Workaround GPIO 1 errata on MPC8572/MPC8536. The status of GPIOs
 * defined as output cannot be determined by reading GPDAT register,
 * so we use shadow data register instead. The status of input pins
 * is determined by reading GPDAT register.
 */

Best Regards,
Liu Gang