linux-kernel - [PATCH v2] Input: reserve 2 events code because of HID

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Date:   Thu,  4 Oct 2018 14:34:30 +0200
From:   Benjamin Tissoires <benjamin.tissoires@...hat.com>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Jiri Kosina <jikos@...nel.org>,
        Harry Cutts <hcutts@...omium.org>,
        Peter Hutterer <peter.hutterer@...-t.net>
Cc:     linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>
Subject: [PATCH v2] Input: reserve 2 events code because of HID

Prior to commit 190d7f02ce8e ("HID: input: do not increment usages when
a duplicate is found") from the v4.18 kernel, HID used to shift the
event codes if a duplicate usage was found. This ended up in a situation
where a device would export a ton of ABS_MISC+n event codes, or a ton
of REL_MISC+n event codes.

This is now fixed, however userspace needs to detect those situation.
Fortunately, ABS_MT_SLOT-1 (ABS_MISC+6) was never assigned a code, and
so libinput can detect fake multitouch devices from genuine ones by
checking if ABS_MT_SLOT-1 is set.

Now that we have REL_WHEEL_HI_RES, libinput won't be able to differentiate
true high res mice from some other device in a pre-v4.18 kernel.

Set in stone that the ABS_MISC+6 and REL_MISC+1 are reserved and should not
be used so userspace can properly work around those old kernels.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@...hat.com>
---

Dmitry, I did not take your Acked-by, as I added 2 new events and wanted to
be sure you are still OK.

Jiri, this will still need to go through your tree, as the input-event-codes
changes that introduce REL_WHEEL_HI_RES are in your for-4.20/logitech-highres.

Cheers,
Benjamin

 include/uapi/linux/input-event-codes.h | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/input-event-codes.h b/include/uapi/linux/input-event-codes.h
index 29fb891ea337..b5e0e9856c47 100644
--- a/include/uapi/linux/input-event-codes.h
+++ b/include/uapi/linux/input-event-codes.h
@@ -708,7 +708,15 @@
 #define REL_DIAL		0x07
 #define REL_WHEEL		0x08
 #define REL_MISC		0x09
-#define REL_WHEEL_HI_RES	0x0a
+/*
+ * 0x0a is reserved and should not be used in input drivers.
+ * It was used by HID as REL_MISC+1 and userspace needs to detect if
+ * the next REL_* event is correct or is just REL_MISC + n.
+ * We define here REL_RESERVED so userspace can rely on it and detect
+ * the situation described above.
+ */
+#define REL_RESERVED		0x0a
+#define REL_WHEEL_HI_RES	0x0b
 #define REL_MAX			0x0f
 #define REL_CNT			(REL_MAX+1)

@@ -745,6 +753,15 @@

 #define ABS_MISC		0x28

+/*
+ * 0x2e is reserved and should not be used in input drivers.
+ * It was used by HID as ABS_MISC+6 and userspace needs to detect if
+ * the next ABS_* event is correct or is just ABS_MISC + n.
+ * We define here ABS_RESERVED so userspace can rely on it and detect
+ * the situation described above.
+ */
+#define ABS_RESERVED		0x2e
+
 #define ABS_MT_SLOT		0x2f	/* MT slot being modified */
 #define ABS_MT_TOUCH_MAJOR	0x30	/* Major axis of touching ellipse */
 #define ABS_MT_TOUCH_MINOR	0x31	/* Minor axis (omit if circular) */
-- 
2.14.3