Re: [PATCH 3/3] [POWERPC] QE: implement GPIO LIB API

[Jochen Friedrich]

Hi Anton,

> +static void qe_gpio_set(struct gpio_chip *gc, unsigned int gpio, int val)
> +{
> +     struct of_mm_gpio_chip *mm_gc = to_of_mm_gpio_chip(gc);
> +     struct port_regs *regs = mm_gc->regs;
> +     u32 pin_mask;
> +     u32 tmp_val;
> +
> +     /* calculate pin location */
> +     pin_mask = (u32) (1 << (NUM_OF_PINS - 1 - gpio));
> +
> +     tmp_val = in_be32(&regs->cpdata);
> +
> +     if (val == 0)
> +             out_be32(&regs->cpdata, ~pin_mask & tmp_val);
> +     else
> +             out_be32(&regs->cpdata, pin_mask | tmp_val);
> +}

I see a possible problem with this (and in the corresponding call in CPM1, as 
well):

if there is a pin configured as open drain, you might accidently switch this 
pin to 0
while switching a different pin, if an external device is pulling the pin to 0.

i2c-gpio.c and w1-gpio.c (in -mm) are examples of drivers which use open drain 
pins
and which would fail if another pin on the same port would be set during a 
transfer.

Thanks,
Jochen
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