[PATCH v2] HID: input: do not run GET_REPORT unless there's a Resolution Multiplier

[Peter Hutterer <peter.hutterer@who-t.net>]

hid-multitouch currently runs GET_REPORT for Contact Max and again to
retrieve the Win8 blob. If both are within the same report, the
Resolution Multiplier code calls GET_FEATURE again and this time,
possibly due to timing, it causes the ILITEK-TP device interpret the
GET_FEATURE as an instruction to change the mode and effectively stop
the device from functioning as expected.

Notably: the device doesn't even have a Resolution Multiplier so it
shouldn't be affected by any of this at all.

Fix this by making sure we only execute GET_REPORT if there is
a Resolution Multiplier in the respective report. Where the
HID_QUIRK_NO_INIT_REPORTS field is set we just bail out immediately. This
shouldn't be triggered by any real device anyway.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Tested-by: Wen He <wen.he_1@nxp.com>
---
Changes to v1:
- bail out in case of HID_QUIRK_NO_INIT_REPORTS

 drivers/hid/hid-input.c | 30 ++++++++++++++++++++----------
 1 file changed, 20 insertions(+), 10 deletions(-)

diff --git a/drivers/hid/hid-input.c b/drivers/hid/hid-input.c
index dea9cc65bf80..c8633beae260 100644
--- a/drivers/hid/hid-input.c
+++ b/drivers/hid/hid-input.c
@@ -1560,21 +1560,12 @@ static bool __hidinput_change_resolution_multipliers(struct hid_device *hid,
 {
 	struct hid_usage *usage;
 	bool update_needed = false;
+	bool get_report_completed = false;
 	int i, j;
 
 	if (report->maxfield == 0)
 		return false;
 
-	/*
-	 * If we have more than one feature within this report we
-	 * need to fill in the bits from the others before we can
-	 * overwrite the ones for the Resolution Multiplier.
-	 */
-	if (report->maxfield > 1) {
-		hid_hw_request(hid, report, HID_REQ_GET_REPORT);
-		hid_hw_wait(hid);
-	}
-
 	for (i = 0; i < report->maxfield; i++) {
 		__s32 value = use_logical_max ?
 			      report->field[i]->logical_maximum :
@@ -1593,6 +1584,25 @@ static bool __hidinput_change_resolution_multipliers(struct hid_device *hid,
 			if (usage->hid != HID_GD_RESOLUTION_MULTIPLIER)
 				continue;
 
+			/*
+			 * If we have more than one feature within this
+			 * report we need to fill in the bits from the
+			 * others before we can overwrite the ones for the
+			 * Resolution Multiplier.
+			 *
+			 * But if we're not allowed to read from the device,
+			 * we just bail. Such a device should not exist
+			 * anyway.
+			 */
+			if (!get_report_completed && report->maxfield > 1) {
+				if (hid->quirks & HID_QUIRK_NO_INIT_REPORTS)
+					return update_needed;
+
+				hid_hw_request(hid, report, HID_REQ_GET_REPORT);
+				hid_hw_wait(hid);
+				get_report_completed = true;
+			}
+
 			report->field[i]->value[j] = value;
 			update_needed = true;
 		}
-- 
2.26.2