HID: wacom: Set eraser status when either 'Eraser' or 'Invert' usage is set

JIRA: https://issues.redhat.com/browse/RHEL-102058
Upstream Status: since v6.13

commit a025b0d
Author: Jason Gerecke <jason.gerecke@wacom.com>
Date:   Thu Oct 17 11:31:13 2024 -0700

    HID: wacom: Set eraser status when either 'Eraser' or 'Invert' usage is set

    Microsoft defines two slightly different behaviors for pens that are
    being used to erase. The first one, for pens that can be used while
    inverted specifies that both 'Invert' and 'Eraser' usages should be
    set while the pen is in contact and erasing. For pens that use an
    eraser button though, they specify that only the 'Eraser' usage should
    be set (while hovering, only the 'Invert' usage is to be set).

    We used our internal 'invert_state' flag to determine if a pen has an
    intent to erase (whether hovering or not). That flag was previously
    only depending on the 'Invert' usage, which was sufficient for the
    first type of pen (EMR) but not the second type (AES). This commit
    makes the flag depend on either usage being set, and also renames it
    to make its function more clear.

    This change should not normally have an impact on userspace due to
    both the existing driver and firmware design. The driver already only
    determines tool type based on the first event in an interaction (e.g.
    it will see the 'Invert' bit set when the eraser comes into prox and
    then report BTN_TOOL_RUBBER for the rest of the interaction, even if
    'Invert' is cleared). AES firmware is also careful to send reports
    that work through a set of defined state transitions, even in the
    corner-case where the eraser button is pressed when the pen is already
    in contact with the display (Prox|Tip -> Prox -> 0 -> Invert -> Eraser).
    Regardless, it seems reasonable to ensure the driver's state variables
    match programmer expectation.

    Link: https://learn.microsoft.com/en-us/windows-hardware/design/component-guidelines/windows-pen-states
    Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
    Signed-off-by: Jiri Kosina <jkosina@suse.com>

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

Author: bentiss

drivers/hid/wacom_wac.c

@@ -2422,9 +2422,11 @@ static void wacom_wac_pen_event(struct hid_device *hdev, struct hid_field *field
 			wacom_wac->hid_data.sense_state = value;
 		return;
 	case HID_DG_INVERT:
-		wacom_wac->hid_data.invert_state = value;
+		wacom_wac->hid_data.eraser |= value;
 		return;
 	case HID_DG_ERASER:
+		wacom_wac->hid_data.eraser |= value;
+		fallthrough;
 	case HID_DG_TIPSWITCH:
 		wacom_wac->hid_data.tipswitch |= value;
 		return;
@@ -2565,7 +2567,7 @@ static void wacom_wac_pen_report(struct hid_device *hdev,
 
 	if (entering_range) { /* first in range */
 		/* Going into range select tool */
-		if (wacom_wac->hid_data.invert_state)
+		if (wacom_wac->hid_data.eraser)
 			wacom_wac->tool[0] = BTN_TOOL_RUBBER;
 		else if (wacom_wac->features.quirks & WACOM_QUIRK_AESPEN)
 			wacom_wac->tool[0] = BTN_TOOL_PEN;
@@ -2619,6 +2621,7 @@ static void wacom_wac_pen_report(struct hid_device *hdev,
 		}
 
 		wacom_wac->hid_data.tipswitch = false;
+		wacom_wac->hid_data.eraser = false;
 
 		input_sync(input);
 	}

drivers/hid/wacom_wac.h

@@ -300,7 +300,7 @@ struct hid_data {
 	__s16 inputmode_index;	/* InputMode HID feature index in the report */
 	bool sense_state;
 	bool inrange_state;
-	bool invert_state;
+	bool eraser;
 	bool tipswitch;
 	bool barrelswitch;
 	bool barrelswitch2;