HID: input: use the Resolution Multiplier for high-resolution scrolling

Windows uses a magic number of 120 for a wheel click. High-resolution
scroll wheels are supposed to use a fraction of 120 to signal smaller
scroll steps. This is implemented by the Resolution Multiplier in the
device itself.

If the multiplier is present in the report descriptor, set it to the
logical max and then use the resolution multiplier to calculate the
high-resolution events. This is the recommendation by Microsoft, see
http://msdn.microsoft.com/en-us/windows/hardware/gg487477.aspx

Note that all mice encountered so far have a logical min/max of 0/1, so
it's a binary "yes or no" to high-res scrolling anyway.

To make userspace simpler, always enable the REL_WHEEL_HI_RES bit. Where
the device doesn't support high-resolution scrolling, the value for the
high-res data will simply be a multiple of 120 every time. For userspace,
if REL_WHEEL_HI_RES is available that is the one to be used.

Potential side-effect: a device with a Resolution Multiplier applying to
other Input items will have those items set to the logical max as well.
This cannot easily be worked around but it is doubtful such devices exist.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Verified-by: Harry Cutts <hcutts@chromium.org>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/hid.h b/include/linux/hid.h
index fd8d860365a4..93db548f8761 100644
--- a/include/linux/hid.h
+++ b/include/linux/hid.h
@@ -233,6 +233,7 @@ struct hid_item {
 #define HID_DC_BATTERYSTRENGTH	0x00060020
 
 #define HID_CP_CONSUMER_CONTROL	0x000c0001
+#define HID_CP_AC_PAN		0x000c0238
 
 #define HID_DG_DIGITIZER	0x000d0001
 #define HID_DG_PEN		0x000d0002
@@ -441,11 +442,13 @@ struct hid_usage {
 	__s8	  resolution_multiplier;/* Effective Resolution Multiplier
 					   (HUT v1.12, 4.3.1), default: 1 */
 	/* hidinput data */
+	__s8	  wheel_factor;		/* 120/resolution_multiplier */
 	__u16     code;			/* input driver code */
 	__u8      type;			/* input driver type */
 	__s8	  hat_min;		/* hat switch fun */
 	__s8	  hat_max;		/* ditto */
 	__s8	  hat_dir;		/* ditto */
+	__s16	  wheel_accumulated;	/* hi-res wheel */
 };
 
 struct hid_input;