HID: multitouch: add control of the feature "Maximum Contact Number"

Some devices, like Perixx Peripad 701 do not work if the feature
"Maximum Contact Number" is not set to the right value.
This patch allows hid-multitouch to control this feature.

If the programmer fills the field maxcontacts in the mt_class,
then the driver will set the feature to this value. It is safe
for current drivers as the feature is read/write in the HID norm
and all devices should implement the norm.
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@enac.fr>
Acked-by: Henrik Rydberg <rydberg@euromail.se>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-multitouch.c

@@ -77,6 +77,8 @@ struct mt_device {
 	unsigned last_slot_field;	/* the last field of a slot */
 	int last_mt_collection;	/* last known mt-related collection */
 	__s8 inputmode;		/* InputMode HID feature, -1 if non-existent */
+	__s8 maxcontact_report_id;	/* Maximum Contact Number HID feature,
+				   -1 if non-existent */
 	__u8 num_received;	/* how many contacts we received */
 	__u8 num_expected;	/* expected last contact index */
 	__u8 maxcontacts;
@@ -242,6 +244,7 @@ static void mt_feature_mapping(struct hid_device *hdev,
 		td->inputmode = field->report->id;
 		break;
 	case HID_DG_CONTACTMAX:
+		td->maxcontact_report_id = field->report->id;
 		td->maxcontacts = field->value[0];
 		if (td->mtclass.maxcontacts)
 			/* check if the maxcontacts is given by the class */
@@ -606,6 +609,32 @@ static void mt_set_input_mode(struct hid_device *hdev)
 	}
 }
 
+static void mt_set_maxcontacts(struct hid_device *hdev)
+{
+	struct mt_device *td = hid_get_drvdata(hdev);
+	struct hid_report *r;
+	struct hid_report_enum *re;
+	int fieldmax, max;
+
+	if (td->maxcontact_report_id < 0)
+		return;
+
+	if (!td->mtclass.maxcontacts)
+		return;
+
+	re = &hdev->report_enum[HID_FEATURE_REPORT];
+	r = re->report_id_hash[td->maxcontact_report_id];
+	if (r) {
+		max = td->mtclass.maxcontacts;
+		fieldmax = r->field[0]->logical_maximum;
+		max = min(fieldmax, max);
+		if (r->field[0]->value[0] != max) {
+			r->field[0]->value[0] = max;
+			usbhid_submit_report(hdev, r, USB_DIR_OUT);
+		}
+	}
+}
+
 static int mt_probe(struct hid_device *hdev, const struct hid_device_id *id)
 {
 	int ret, i;
@@ -631,6 +660,7 @@ static int mt_probe(struct hid_device *hdev, const struct hid_device_id *id)
 	}
 	td->mtclass = *mtclass;
 	td->inputmode = -1;
+	td->maxcontact_report_id = -1;
 	td->last_mt_collection = -1;
 	hid_set_drvdata(hdev, td);
 
@@ -653,6 +683,7 @@ static int mt_probe(struct hid_device *hdev, const struct hid_device_id *id)
 
 	ret = sysfs_create_group(&hdev->dev.kobj, &mt_attribute_group);
 
+	mt_set_maxcontacts(hdev);
 	mt_set_input_mode(hdev);
 
 	return 0;
@@ -665,6 +696,7 @@ static int mt_probe(struct hid_device *hdev, const struct hid_device_id *id)
 #ifdef CONFIG_PM
 static int mt_reset_resume(struct hid_device *hdev)
 {
+	mt_set_maxcontacts(hdev);
 	mt_set_input_mode(hdev);
 	return 0;
 }