This is a note to let you know that I've just added the patch titled HID: wacom: Ignore attempts to overwrite the touch_max value from HID to the 5.10-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: hid-wacom-ignore-attempts-to-overwrite-the-touch_max-value-from-hid.patch and it can be found in the queue-5.10 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 88f38846bfb1a452a3d47e38aeab20a4ceb74294 Mon Sep 17 00:00:00 2001 From: Jason Gerecke <killertofu@xxxxxxxxx> Date: Tue, 16 Feb 2021 11:41:54 -0800 Subject: HID: wacom: Ignore attempts to overwrite the touch_max value from HID From: Jason Gerecke <killertofu@xxxxxxxxx> commit 88f38846bfb1a452a3d47e38aeab20a4ceb74294 upstream. The `wacom_feature_mapping` function is careful to only set the the touch_max value a single time, but this care does not extend to the `wacom_wac_finger_event` function. In particular, if a device sends multiple HID_DG_CONTACTMAX items in a single feature report, the driver will end up retaining the value of last item. The HID descriptor for the Cintiq Companion 2 does exactly this. It incorrectly sets a "Report Count" of 2, which will cause the driver to process two HID_DG_CONTACTCOUNT items. The first item has the actual count, while the second item should have been declared as a constant zero. The constant zero is the value the driver ends up using, however, since it is the last HID_DG_CONTACTCOUNT in the report. Report ID (16), Usage (Contact Count Maximum), ; Contact count maximum (55h, static value) Report Count (2), Logical Maximum (10), Feature (Variable), To address this, we add a check that the touch_max is not already set within the `wacom_wac_finger_event` function that processes the HID_DG_TOUCHMAX item. We emit a warning if the value is set and ignore the updated value. This could potentially cause problems if there is a tablet which has a similar issue but requires the last item to be used. This is unlikely, however, since it would have to have a different non-zero value for HID_DG_CONTACTMAX earlier in the same report, which makes no sense except in the case of a firmware bug. Note that cases where the HID_DG_CONTACTMAX items are in different reports is already handled (and similarly ignored) by `wacom_feature_mapping` as mentioned above. Link: https://github.com/linuxwacom/input-wacom/issues/223 Fixes: 184eccd40389 ("HID: wacom: generic: read HID_DG_CONTACTMAX from any feature report") Signed-off-by: Jason Gerecke <jason.gerecke@xxxxxxxxx> CC: stable@xxxxxxxxxxxxxxx Signed-off-by: Jiri Kosina <jkosina@xxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/hid/wacom_wac.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) --- a/drivers/hid/wacom_wac.c +++ b/drivers/hid/wacom_wac.c @@ -2600,7 +2600,12 @@ static void wacom_wac_finger_event(struc wacom_wac->is_invalid_bt_frame = !value; return; case HID_DG_CONTACTMAX: - features->touch_max = value; + if (!features->touch_max) { + features->touch_max = value; + } else { + hid_warn(hdev, "%s: ignoring attempt to overwrite non-zero touch_max " + "%d -> %d\n", __func__, features->touch_max, value); + } return; } Patches currently in stable-queue which might be from killertofu@xxxxxxxxx are queue-5.10/hid-wacom-ignore-attempts-to-overwrite-the-touch_max-value-from-hid.patch