On 10/07/2017 06:07 AM, Linus Walleij wrote:

I mean that you add
unsigned long *line_valid_mask;
to struct gpio_chip using the same type of logic
as .irq_valid_mask. The mask should be optional.

Then the operation gpiod_get[_index]() will FAIL if the
line is not valid.

There is no need to check on every operation, there should
be no way to get a handle on the pin any other way.

All new code should be using descriptors at this point so we
only need to design for that case.

I think I'm missing something, because I implemented what you're asking 
for, but whenever I try to expose a GPIO from sysfs (e.g. echo 37 > 
/sys/class/gpio/export), gpiod_get_index() is not called.  The only 
thing preventing the GPIO from being exported is the ->request callback:

static int msm_gpio_request(struct gpio_chip *chip, unsigned int offset)
{
	struct msm_pinctrl *pctrl = gpiochip_get_data(chip);
	const struct msm_pingroup *g = &pctrl->soc->groups[offset];

	if (!g->npins)
		return -ENODEV;

What operation is supposed to trigger a call to gpiod_get_index?

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