Re: [PATCH v3] HID: i2c-hid: add polling mode based on connected GPIO chip's pin status

["Barnabás Pőcze" <pobrn@protonmail.com>]

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.


> [...]
> +/* 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?


> +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.


> +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) ")"


> [...]
> +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.


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

Same here.


> +	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.


> +
> +	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.


> +		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())`.


> +
> +		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.


> +	}
> +
> +	do_exit(0);

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


> +	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;
```


> +}
> [...]


Regards,
Barnabás Pőcze