Hi,

On Thu, Oct 22, 2020 at 02:22:51PM +0000, Barnabás Pőcze wrote:

Hi,

I think this looks a lot better than the first version, the issues around
suspend/resume are sorted out as far as I can see. However, I still have a couple
comments, mainly minor ones.

Thank you for reviewing this patch!

quoted

[...]
+/* polling mode */
+#define I2C_HID_POLLING_DISABLED 0
+#define I2C_HID_POLLING_GPIO_PIN 1
+#define I2C_HID_POLLING_INTERVAL_ACTIVE_US 4000
+#define I2C_HID_POLLING_INTERVAL_IDLE_MS 10
+
+static u8 polling_mode;
+module_param(polling_mode, byte, 0444);
+MODULE_PARM_DESC(polling_mode, "How to poll - 0 disabled; 1 based on GPIO pin's status");
+

Minor thing, but maybe the default value should be documented in the parameter
description?

quoted

+static unsigned int polling_interval_active_us = I2C_HID_POLLING_INTERVAL_ACTIVE_US;
+module_param(polling_interval_active_us, uint, 0644);
+MODULE_PARM_DESC(polling_interval_active_us,
+		 "Poll every {polling_interval_active_us} us when the touchpad is active. Default to 4000 us");
+
+static unsigned int polling_interval_idle_ms = I2C_HID_POLLING_INTERVAL_IDLE_MS;

Since these two parameters are mostly read, I think the `__read_mostly`
attribute (linux/cache.h) is justified here.

quoted

+module_param(polling_interval_idle_ms, uint, 0644);
+MODULE_PARM_DESC(polling_interval_idle_ms,
+		 "Poll every {polling_interval_idle_ms} ms when the touchpad is idle. Default to 10 ms");

This is minor stylistic thing; as far as I see, the prevalent pattern is to put
the default value at the end, in parenthesis:
E.g. "some parameter description (default=X)" or "... (default: X)" or something similar

Maybe __stringify() (linux/stringify.h) could be used here and for the previous
module parameter?

E.g. "... (default=" __stringify(I2C_HID_POLLING_INTERVAL_IDLE_MS) ")"

Thank you for the above three suggestions! Will be applied in v4.

quoted

[...]
+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);

Can the trigger type change? Because if not, then I think it'd be better to store
the value somewhere and not query it every time.

The irq trigger type is obtained from ACPI so I don't think it won't
change.

quoted

+	struct irq_desc *irq_desc = irq_to_desc(client->irq);

Same here.

Thank you for the reminding!

quoted

+	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.

quoted

+
+	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.

quoted

+		return false;
+	}
+	/*
+	 * 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 !status;
+
+	return status;
+}
+
+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) {
+		if (kthread_should_stop())
+			break;

I think this should be `while (!kthread_should_stop())`.

This simplifies the code. Thank you!

quoted

+
+		while (interrupt_line_active(client) &&
+		       !test_bit(I2C_HID_READ_PENDING, &ihid->flags) &&
+		       !kthread_should_stop()) {
+			i2c_hid_get_input(ihid);
+			usleep_range(polling_interval_active_us,
+				     polling_interval_active_us + 100);
+		}
+		/*
+		 * 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;
+		usleep_range(polling_interval_idle,
+			     polling_interval_idle + 1000);

I don't quite understand why you use an extra variable here. I'm assuming
you want to "save" a multiplication? I believe the compiler will optimize it
to a single read, and single multiplication regardless whether you use a "temporary"
variable or not.

quoted

+	}
+
+	do_exit(0);

Looking at other examples, I don't think `do_exit()` is necessary.

According to the doc of kthread_create_on_node,
     @threadfn() can either call do_exit() directly if it is a
     * standalone thread for which no one will call kthread_stop(), or
     * return when 'kthread_should_stop()' is true (which means
     * kthread_stop() has been called).

do_exit is not necessary. Thank you for raising up this issue and
looking at other examples for me!

quoted

+	return 0;
+}
+
+static int i2c_hid_init_polling(struct i2c_hid *ihid)
+{
+	struct i2c_client *client = ihid->client;
+
+	if (!irq_get_trigger_type(client->irq)) {
+		dev_warn(&client->dev,
+			 "Failed to get GPIO Interrupt Assertion Level, could not enable polling mode for %s",
+			 client->name);
+		return -EINVAL;
+	}
+
+	ihid->polling_thread = kthread_create(i2c_hid_polling_thread, ihid,
+					      "I2C HID polling thread");
+
+	if (!IS_ERR(ihid->polling_thread)) {
+		pr_info("I2C HID polling thread created");
+		wake_up_process(ihid->polling_thread);
+		return 0;
+	}
+
+	return PTR_ERR(ihid->polling_thread);

I would personally rewrite this parts as

if (IS_ERR(...)) {
 dev_err(...);
 return PTR_ERR(...);
}
....
return 0;

Thank you! This style is consistent with other functions in this file.

quoted

+}
[...]

Regards,
Barnabás Pőcze

--
Best regards,
Coiby