Hi
2020. november 22., vasárnap 11:15 keltezéssel, Coiby Xu írta:
> [...]
> >> +static int get_gpio_pin_state(struct irq_desc *irq_desc)
> >> +{
> >> + struct gpio_chip *gc = irq_data_get_irq_chip_data(&irq_desc->irq_data);
> >> +
> >> + return gc->get(gc, irq_desc->irq_data.hwirq);
> >> +}
> [...]
> >> + ssize_t status = get_gpio_pin_state(irq_desc);
> >
> >`get_gpio_pin_state()` returns an `int`, so I am not sure why `ssize_t` is used here.
> >
>
> I used `ssize_t` because I found gpiolib-sysfs.c uses `ssize_t`
>
> // drivers/gpio/gpiolib-sysfs.c
> static ssize_t value_show(struct device *dev,
> struct device_attribute *attr, char *buf)
> {
> struct gpiod_data *data = dev_get_drvdata(dev);
> struct gpio_desc *desc = data->desc;
> ssize_t status;
>
> mutex_lock(&data->mutex);
>
> status = gpiod_get_value_cansleep(desc);
> ...
> return status;
> }
>
> According to the book Advanced Programming in the UNIX Environment by
> W. Richard Stevens,
> With the 1990 POSIX.1 standard, the primitive system data type
> ssize_t was introduced to provide the signed return value...
>
> So ssize_t is fairly common, for example, the read and write syscall
> return a value of type ssize_t. But I haven't found out why ssize_t is
> better int.
> >
Sorry if I wasn't clear, what prompted me to ask that question is the following:
`gc->get()` returns `int`, `get_gpio_pin_state()` returns `int`, yet you still
save the return value of `get_gpio_pin_state()` into a variable with type
`ssize_t` for no apparent reason. In the example you cited, `ssize_t` is used
because the show() callback of a sysfs attribute must return `ssize_t`, but here,
`interrupt_line_active()` returns `bool`, so I don't see any advantage over a
plain `int`. Anyways, I believe either one is fine, I just found it odd.
> >> +
> >> + if (status < 0) {
> >> + dev_warn(&client->dev,
> >> + "Failed to get GPIO Interrupt line status for %s",
> >> + client->name);
> >
> >I think it's possible that the kernel message buffer is flooded with these
> >messages, which is not optimal in my opinion.
> >
> Thank you! Replaced with dev_dbg in v4.
> [...]
Have you looked at `dev_{warn,dbg,...}_ratelimited()`?
Regards,
Barnabás Pőcze
