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

Hi

[...]

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+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.

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I read the code of a couple gpio chips and - I may be wrong, but - it seems they
can return an arbitrary errno.

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+
+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?

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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.

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+			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;
+}

[...]

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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