[PATCH 4/4] HID: input: work around Win8 stylus-on-touchscreen reporting

[Ahelenia Ziemiańska]

With this, these devices now behave as tablets as expected by userspace

Signed-off-by: Ahelenia Ziemiańska <nabijaczlew...@nabijaczleweli.xyz>
---
 drivers/hid/hid-input.c | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/drivers/hid/hid-input.c b/drivers/hid/hid-input.c
index a5ba92978473..b8813fc3e9d2 100644
--- a/drivers/hid/hid-input.c
+++ b/drivers/hid/hid-input.c
@@ -1273,6 +1273,41 @@ static void hidinput_handle_scroll(struct hid_usage 
*usage,
        input_event(input, EV_REL, usage->code, hi_res);
 }
 
+/*
+ * Win8 tablet stylus devices send, in order:
+ *   HID_DG_TIPSWITCH (BTN_TOUCH)
+ *   HID_DG_INVERT    (BTN_TOOL_RUBBER)
+ *   HID_DG_ERASER    (BTN_TOUCH)
+ *   HID_DG_INRANGE   (BTN_TOOL_PEN)
+ *
+ * For each of these states:
+ *   hover     :                         INRANGE
+ *   touching  : TIPSWITCH
+ *   hover+2   :           INVERT        INRANGE
+ *   touching+2:                  ERASER INRANGE
+ *
+ * Which means we'd send BTN_TOUCH=0 + BTN_TOOL_PEN=1 on proximity,
+ * then BTN_TOUCH=1 and BTN_TOOL_PEN=0 in consecutive groups when touched,
+ * indicating the stylus leaving the screen as soon as the two meet.
+ */
+static void hidinput_fixup_win8_inrange(struct hid_device *hid, struct 
hid_field *field, __s32 *value)
+{
+       unsigned f, u;
+       struct hid_field *rfield;
+
+       if (!*value) {
+               for (f = 0; f < field->report->maxfield; ++f) {
+                       rfield = field->report->field[f];
+                       for (u = 0; u < rfield->maxusage; ++u) {
+                               if (rfield->usage[u].hid == HID_DG_TIPSWITCH) {
+                                       *value = rfield->value[u];
+                                       return;
+                               }
+                       }
+               }
+       }
+}
+
 void hidinput_hid_event(struct hid_device *hid, struct hid_field *field, 
struct hid_usage *usage, __s32 value)
 {
        struct input_dev *input;
@@ -1306,7 +1341,13 @@ void hidinput_hid_event(struct hid_device *hid, struct 
hid_field *field, struct
                return;
        }
 
+       if (usage->hid == HID_DG_ERASER && value)
+               *quirks |= HID_QUIRK_INVERT;
+
        if (usage->hid == HID_DG_INRANGE) {
+               if (hid->group == HID_GROUP_MULTITOUCH_WIN_8)
+                       hidinput_fixup_win8_inrange(hid, field, &value);
+
                if (value) {
                        input_event(input, usage->type, (*quirks & 
HID_QUIRK_INVERT) ? BTN_TOOL_RUBBER : usage->code, 1);
                        return;
-- 
2.20.1

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