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.
> >> +
> >> +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.
> >> + 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.
> [...]
Regards,
Barnabás Pőcze
