HID: wacom: Tie cached HID_DG_CONTACTCOUNT indices to report ID

The cached indicies 'cc_index' and 'cc_value_index' introduced in 1b5d514 are only valid for a single report ID. If a touchscreen has multiple reports with a HID_DG_CONTACTCOUNT usage, its possible that the values will not be correct for the report we're handling, resulting in an incorrect value for 'num_expected'. This has been observed with the Cintiq Companion 2.

To address this, we store the ID of the report those indicies are valid for in a new 'cc_report' variable. Before using them to get the expected contact count, we first check if the ID of the report we're processing matches 'cc_report'. If it doesn't, we update the indicies to point to the HID_DG_CONTACTCOUNT usage of the current report (if it has one).

---
Jiri,

Could you please queue this patch and the next for 4.3? They fix issues with the implementation of my "Ignore contacts in excess of declared contact count" patch which was pulled in as part of the 4.3 merge window.

Thanks :)

 drivers/hid/wacom_wac.c | 26 ++++++++++++++++++++++++++
 drivers/hid/wacom_wac.h |  1 +
 2 files changed, 27 insertions(+)

index c40a6d1..4140b1d 100644
@@ -1628,6 +1628,7 @@ static void wacom_wac_finger_usage_mapping(struct hid_device *hdev,
 		wacom_map_usage(input, usage, field, EV_KEY, BTN_TOUCH, 0);
 		break;
 	case HID_DG_CONTACTCOUNT:
+		wacom_wac->hid_data.cc_report = field->report->id;
 		wacom_wac->hid_data.cc_index = field->index;
 		wacom_wac->hid_data.cc_value_index = usage->usage_index;
 		break;

@@ -1715,6 +1716,31 @@ static void wacom_wac_finger_pre_report(struct hid_device *hdev,
 	struct wacom_wac *wacom_wac = &wacom->wacom_wac;
 	struct hid_data* hid_data = &wacom_wac->hid_data;
 
+	if (hid_data->cc_report != 0 &&
+	    hid_data->cc_report != report->id) {
+		int i;
+
+		hid_data->cc_report = report->id;
+		hid_data->cc_index = -1;
+		hid_data->cc_value_index = -1;
+
+		for (i = 0; i < report->maxfield; i++) {
+			struct hid_field *field = report->field[i];
+			int j;
+
+			for (j = 0; j < field->maxusage; j++) {
+				if (field->usage[j].hid == HID_DG_CONTACTCOUNT) {
+					hid_data->cc_index = i;
+					hid_data->cc_value_index = j;
+
+					/* break */
+					i = report->maxfield;
+					j = field->maxusage;
+				}
+			}
+		}
+	}
+
 	if (hid_data->cc_index >= 0) {
 		struct hid_field *field = report->field[hid_data->cc_index];
 		int value = field->value[hid_data->cc_value_index];

index 1e270d4..809c03e 100644
@@ -198,6 +198,7 @@ struct hid_data {
 	int width;
 	int height;
 	int id;
+	int cc_report;
 	int cc_index;
 	int cc_value_index;
 	int num_expected;

2.6.1

When introduced in commit 1b5d514, the check 'if (hid_data->cc_index >= 0)' in 'wacom_wac_finger_pre_report' was intended to switch where the driver got the expected number of contacts from: HID_DG_CONTACTCOUNT if the usage was present, or 'touch_max' otherwise. Unfortunately, an oversight worthy of a brown paper bag (specifically, that 'cc_index' could never be negative) meant that the latter 'else' clause would never be entered.

The patch prior to this one introduced a way for 'cc_index' to be negative, but only if HID_DG_CONTACTCOUNT is present in some report _other_ than the one being processed. To ensure the 'else' clause is also entered for devices which don't have HID_DG_CONTACTCOUNT on _any_ report, we add the additional constraint that 'cc_report' be non-zero (which is true only if the usage is present in some report).

---
Jiri,

Could you please queue this patch and the prior for 4.3? They fix issues with the implementation of my "Ignore contacts in excess of declared contact count" patch which was pulled in as part of the 4.3 merge window.

Thanks :)

 drivers/hid/wacom_wac.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

index 4140b1d..46bd02b 100644
@@ -1740,8 +1740,8 @@ static void wacom_wac_finger_pre_report(struct hid_device *hdev,
 			}
 		}
 	}
-
-	if (hid_data->cc_index >= 0) {
+	if (hid_data->cc_report != 0 &&
+	    hid_data->cc_index >= 0) {
 		struct hid_field *field = report->field[hid_data->cc_index];
 		int value = field->value[hid_data->cc_value_index];
 		if (value)

2.6.1

Alright, I've applied this to for-4.3/upstream-fixes, but it's now very late in the cycle, so I am not 100% sure this patch will make it into 4.3. Hence I've added -stable annotation to it so that it's picked by first 4.3-stable afterwards in such case.

Jiri Kosina
SUSE Labs