Re: [PATCH 4/5] HID: apple-ibridge: Add Apple iBridge HID driver for T1 chip.

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Sat, 27 Feb 2021 17:26:42 -0800
Ronald Tschalär <ronald@innovation.ch> wrote:

> The iBridge device provides access to several devices, including:
> - the Touch Bar
> - the iSight webcam
> - the light sensor
> - the fingerprint sensor
> 
> This driver provides the core support for managing the iBridge device
> and the access to the underlying devices. In particular, the
> functionality for the touch bar and light sensor is exposed via USB HID
> interfaces, and on devices with the T1 chip one of the HID devices is
> used for both functions. So this driver creates virtual HID devices, one
> per top-level report collection on each HID device (for a total of 3
> virtual HID devices). The sub-drivers then bind to these virtual HID
> devices.
> 
> This way the Touch Bar and ALS drivers can be kept in their own modules,
> while at the same time making them look very much like as if they were
> connected to the real HID devices. And those drivers then work (mostly)
> without further changes on MacBooks with the T2 chip that don't need
> this driver.
> 
> Signed-off-by: Ronald Tschalär <ronald@innovation.ch>
Hi Ronald.

This is far from my specialty but mostly looks sensible to me.

Just one thing stood out that I couldn't understand. See below.

Jonathan

> new file mode 100644
> index 0000000000000..5f2b71c199746
> --- /dev/null
> +++ b/drivers/hid/apple-ibridge.c
> @@ -0,0 +1,682 @@

...

> +
> +#ifdef CONFIG_PM
> +/**
> + * appleib_forward_int_op() - Forward a hid-driver callback to all drivers on
> + * all virtual HID devices attached to the given real HID device.
> + * @hdev the real hid-device
> + * @forward a function that calls the callback on the given driver
> + * @args arguments for the forward function
> + *
> + * This is for callbacks that return a status as an int.
> + *
> + * Returns: 0 on success, or the first error returned by the @forward function.
> + */
> +static int appleib_forward_int_op(struct hid_device *hdev,
> +				  int (*forward)(struct hid_driver *,
> +						 struct hid_device *, void *),
> +				  void *args)
> +{
> +	struct appleib_hid_dev_info *hdev_info = hid_get_drvdata(hdev);
> +	struct hid_device *sub_hdev;
> +	int rc = 0;
> +	int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(hdev_info->sub_hdevs); i++) {
> +		sub_hdev = hdev_info->sub_hdevs[i];
> +		if (sub_hdev->driver) {
> +			rc = forward(sub_hdev->driver, sub_hdev, args);
> +			if (rc)
> +				break;

return rc; here would be cleaner.

> +		}
> +
> +		break;

This is unusual.  It's a for loop but as far as I can see only first iteration
can ever run as we exit the loop at this break if we haven't done so earlier.
What is the intent here?

> +	}
> +
> +	return rc;
> +}