From abb36fe691b28f2a64926b61448d6b9610ed879a Mon Sep 17 00:00:00 2001 From: Ben Chan Date: Tue, 29 May 2018 15:56:55 -0700 Subject: [PATCH] HID: multitouch: fix calculation of last slot field in multi-touch reports According to [1] and also seemingly agreed by [2], the Scan Time usage (0x0D 0x56) is a report level usage, not a contact level usage. However, the hid-multitouch driver currently includes HID_DG_SCANTIME when calculating `td->last_slot_field', which may lead to mt_complete_slot() being prematurely called in certain cases (e.g. when each touch input report includes more than one contact and the Scan Time usage appears before any contact logical collection). This patch fixes the issue by skipping mt_store_field() on HID_DG_SCANTIME, similar to how HID_DG_CONTACTCOUNT and HID_DG_CONTACTMAX are handled. [1] https://docs.microsoft.com/en-us/windows-hardware/design/component-guidelines/windows-precision-touchpad-required-hid-top-level-collections#windows-precision-touchpad-input-reports [2] https://patchwork.kernel.org/patch/1742181/ Fixes: 29cc309d8bf19 ("HID: hid-multitouch: forward MSC_TIMESTAMP") Signed-off-by: Ben Chan Reviewed-by: Dmitry Torokhov Signed-off-by: Jiri Kosina --- drivers/hid/hid-multitouch.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/drivers/hid/hid-multitouch.c b/drivers/hid/hid-multitouch.c index 38c4ca2..45968f7 100644 --- a/drivers/hid/hid-multitouch.c +++ b/drivers/hid/hid-multitouch.c @@ -598,13 +598,16 @@ static int mt_touch_input_mapping(struct hid_device *hdev, struct hid_input *hi, hid_map_usage(hi, usage, bit, max, EV_MSC, MSC_TIMESTAMP); input_set_capability(hi->input, EV_MSC, MSC_TIMESTAMP); - mt_store_field(usage, td, hi); /* Ignore if indexes are out of bounds. */ if (field->index >= field->report->maxfield || usage->usage_index >= field->report_count) return 1; td->scantime_index = field->index; td->scantime_val_index = usage->usage_index; + /* + * We don't set td->last_slot_field as scan time is + * global to the report. + */ return 1; case HID_DG_CONTACTCOUNT: /* Ignore if indexes are out of bounds. */ -- 2.7.4