HID: wacom: Reset expected and received contact counts at the same time

Linux Kernel / Linux Kernel - Jason Gerecke [gmail.com] - 21 January 2022 14:10 UTC

These two values go hand-in-hand and must be valid for the driver to behave correctly. We are currently lazy about updating the values and rely on the "expected" code flow to take care of making sure they're
valid at the point they're needed. The "expected" flow changed somewhat with commit f8b6a74719b5 ("HID: wacom: generic: Support multiple tools per report"), however. This led to problems with the DTH-2452 due (in part) to *all* contacts being fully processed -- even those past the expected contact count. Specifically, the received count gets reset to 0 once all expected fingers are processed, but not the expected count. The rest of the contacts in the report are then *also* processed since now the driver thinks we've only processed 0 of N expected contacts.

Later commits such as 7fb0413baa7f (HID: wacom: Use "Confidence" flag to prevent reporting invalid contacts) worked around the DTH-2452 issue by skipping the invalid contacts at the end of the report, but this is not a complete fix. The confidence flag cannot be relied on when a contact is removed (see the following patch), and dealing with that condition re-introduces the DTH-2452 issue unless we also address this contact count laziness. By resetting expected and received counts at the same time we ensure the driver understands that there are 0 more contacts expected in the report. Similarly, we also make sure to reset the received count if for some reason we're out of sync in the pre-report phase.

Link: https://github.com/linuxwacom/input-wacom/issues/288 Fixes: f8b6a74719b5 ("HID: wacom: generic: Support multiple tools per report") CC: stable@vger.kernel.org

546e41ac994c HID: wacom: Reset expected and received contact counts at the same time
drivers/hid/wacom_wac.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

Upstream: git.kernel.org


  • Share