Re: [PATCH v2] HID: i2c-hid: add polling mode based on connected GPIO chip's pin status

[Coiby Xu]

Hi,

On Sat, Oct 17, 2020 at 01:06:14PM +0000, Barnabás Pőcze wrote:
> Hi
>
> > [...]
> > >> +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);
> > >> +}
> > >> +
> > >> +static bool interrupt_line_active(struct i2c_client *client)
> > >> +{
> > >> +	unsigned long trigger_type = irq_get_trigger_type(client->irq);
> > >> +	struct irq_desc *irq_desc = irq_to_desc(client->irq);
> > >> +
> > >> +	/*
> > >> +	 * According to Windows Precsiontion Touchpad's specs
> > >> +	 * https://docs.microsoft.com/en-us/windows-hardware/design/component-guidelines/windows-precision-touchpad-device-bus-connectivity,
> > >> +	 * GPIO Interrupt Assertion Leve could be either ActiveLow or
> > >> +	 * ActiveHigh.
> > >> +	 */
> > >> +	if (trigger_type & IRQF_TRIGGER_LOW)
> > >> +		return !get_gpio_pin_state(irq_desc);
> > >> +
> > >> +	return get_gpio_pin_state(irq_desc);
> > >> +}
> > >
> > >Excuse my ignorance, but I think some kind of error handling regarding the return
> > >value of `get_gpio_pin_state()` should be present here.
> > >
> > What kind of errors would you expect? It seems (struct gpio_chip *)->get
> > only return 0 or 1.
> > >
>
> I read the code of a couple gpio chips and - I may be wrong, but - it seems they
> can return an arbitrary errno.
I thought all GPIO chip return 0 or 1 since !!val is returned. I find
an example which could return negative value,

// drivers/gpio/gpio-wm8994.c
static int wm8994_gpio_get(struct gpio_chip *chip, unsigned offset)
{
	struct wm8994_gpio *wm8994_gpio = gpiochip_get_data(chip);
	struct wm8994 *wm8994 = wm8994_gpio->wm8994;
	int ret;

	ret = wm8994_reg_read(wm8994, WM8994_GPIO_1 + offset);
	if (ret < 0)
		return ret;

	if (ret & WM8994_GPN_LVL)
		return 1;
	else
		return 0;
}
> > >> +
> > >> +static int i2c_hid_polling_thread(void *i2c_hid)
> > >> +{
> > >> +	struct i2c_hid *ihid = i2c_hid;
> > >> +	struct i2c_client *client = ihid->client;
> > >> +	unsigned int polling_interval_idle;
> > >> +
> > >> +	while (1) {
> > >> +		/*
> > >> +		 * re-calculate polling_interval_idle
> > >> +		 * so the module parameters polling_interval_idle_ms can be
> > >> +		 * changed dynamically through sysfs as polling_interval_active_us
> > >> +		 */
> > >> +		polling_interval_idle = polling_interval_idle_ms * 1000;
> > >> +		if (test_bit(I2C_HID_READ_PENDING, &ihid->flags))
> > >> +			usleep_range(50000, 100000);
> > >> +
> > >> +		if (kthread_should_stop())
> > >> +			break;
> > >> +
> > >> +		while (interrupt_line_active(client)) {
> > >
> > >I realize it's quite unlikely, but can't this be a endless loop if data is coming
> > >in at a high enough rate? Maybe the maximum number of iterations could be limited here?
> > >
> > If we find HID reports are constantly read and send to front-end
> > application like libinput, won't it help expose the problem of the I2C
> > HiD device?
> > >
>
> I'm not sure I completely understand your point. The reason why I wrote what I wrote
> is that this kthread could potentially could go on forever (since `kthread_should_stop()`
> is not checked in the inner while loop) if the data is supplied at a high enough rate.
> That's why I said, to avoid this problem, only allow a certain number of iterations
> for the inner loop, to guarantee that the kthread can stop in any case.
I mean if "data is supplied at a high enough rate" does happen, this is
an abnormal case and indicates a bug. So we shouldn't cover it up. We
expect the user to report it to us.
> > >> +			i2c_hid_get_input(ihid);
> > >> +			usleep_range(polling_interval_active_us,
> > >> +				     polling_interval_active_us + 100);
> > >> +		}
> > >> +
> > >> +		usleep_range(polling_interval_idle,
> > >> +			     polling_interval_idle + 1000);
> > >> +	}
> > >> +
> > >> +	do_exit(0);
> > >> +	return 0;
> > >> +}
> > [...]
> > >Excuse my ignorance, but I do not understand why the following two changes are not enough:
> > >
> > >in `i2c_hid_suspend()`:
> > > if (polling_mode == I2C_POLLING_DISABLED)
> > >   disable_irq(client->irq);
> > >
> > >in `i2c_hid_resume()`:
> > > if (polling_mode == I2C_POLLING_DISABLED)
> > >   enable_irq(client->irq);
> > >
> > I think we shouldn't call enable/disable_irq_wake in polling mode
> > where we don't set up irq.
>
> I think I now understand what you mean. I'm not sure, but it seems logical to me
> that you can enable/disable irq wake regardless whether any irq handlers are
> registered or not. Therefore, I figure it makes sense to take the safe path,
> and don't touch irq wake when polling, just as you did.

Thank you for offering your understandings on this patch. When I'm going
to submit next version, I will add a "Signed-off-by" tag with your name
and email, does it look good to you?
> > [...]
>
>
> Regards,
> Barnabás Pőcze

--
Best regards,
Coiby