On Sun, Nov 22, 2020 at 01:33:01PM +0000, Barnabás Pőcze wrote:
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.
I don't understand why "the show() callback of a sysfs attribute
must return `ssize_t`" instead of int. Do you think the rationale
behind it is the same for this case? If yes, using "ssize_t" for
status could be justified.
>> +
>> + 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()`?
Thank you for pointing me to these functions!
Regards,
Barnabás Pőcze
--
Best regards,
Coiby
