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Input: wacom - add some comments to wacom_parse_hid

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Signed-off-by: Chris Bagwell <chris@cnpbagwell.com>
Acked-by: Ping Cheng <pingc@wacom.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
This commit is contained in:
Chris Bagwell 2011-10-26 22:26:59 -07:00 committed by Dmitry Torokhov
parent fc72bf758f
commit 428f85884b
1 changed files with 36 additions and 1 deletions
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37
drivers/input/tablet/wacom_sys.c
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@ -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++;