Messages in this thread | | | From | Coiby Xu <> | Date | Mon, 23 Nov 2020 22:36:13 +0800 | Subject | Re: [PATCH v3] HID: i2c-hid: add polling mode based on connected GPIO chip's pin status |
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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
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