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Commit 428f8588 authored by Chris Bagwell's avatar Chris Bagwell Committed by Dmitry Torokhov
Browse files

Input: wacom - add some comments to wacom_parse_hid 



Signed-off-by: default avatarChris Bagwell <chris@cnpbagwell.com>
Acked-by: default avatarPing Cheng <pingc@wacom.com>
Signed-off-by: default avatarDmitry Torokhov <dtor@mail.ru>
parent fc72bf75

drivers/input/tablet/wacom_sys.c

+36 −1
Original line number Diff line number Diff line
@@ -165,7 +165,37 @@ static void wacom_close(struct input_dev *dev) 
		usb_autopm_put_interface(wacom->intf);

}



static int wacom_parse_hid(struct usb_interface *intf, struct hid_descriptor *hid_desc,

/*

 * Interface Descriptor of wacom devices can be incomplete and

 * inconsistent so wacom_features table is used to store stylus

 * device's packet lengths, various maximum values, and tablet

 * resolution based on product ID's.

 *

 * For devices that contain 2 interfaces, wacom_features table is

 * inaccurate for the touch interface.  Since the Interface Descriptor

 * for touch interfaces has pretty complete data, this function exists

 * to query tablet for this missing information instead of hard coding in

 * an additional table.

 *

 * A typical Interface Descriptor for a stylus will contain a

 * boot mouse application collection that is not of interest and this

 * function will ignore it.

 *

 * It also contains a digitizer application collection that also is not

 * of interest since any information it contains would be duplicate

 * of what is in wacom_features. Usually it defines a report of an array

 * of bytes that could be used as max length of the stylus packet returned.

 * If it happens to define a Digitizer-Stylus Physical Collection then

 * the X and Y logical values contain valid data but it is ignored.

 *

 * A typical Interface Descriptor for a touch interface will contain a

 * Digitizer-Finger Physical Collection which will define both logical

 * X/Y maximum as well as the physical size of tablet. Since touch

 * interfaces haven't supported pressure or distance, this is enough

 * information to override invalid values in the wacom_features table.

 */

static int wacom_parse_hid(struct usb_interface *intf,

			   struct hid_descriptor *hid_desc,

			   struct wacom_features *features)

{

	struct usb_device *dev = interface_to_usbdev(intf);
@@ -306,6 +336,11 @@ static int wacom_parse_hid(struct usb_interface *intf, struct hid_descriptor *hi 
				i++;

				break;



			/*

			 * Requiring Stylus Usage will ignore boot mouse

			 * X/Y values and some cases of invalid Digitizer X/Y

			 * values commonly reported.

			 */

			case HID_USAGE_STYLUS:

				pen = 1;

				i++;