linux-kernel - [PATCH] HID: hid-input: avoid splitting keyboard, system and consumer controls

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Date:   Wed, 13 Jan 2021 22:24:13 -0800
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Jiri Kosina <jikos@...nel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>
Cc:     Peter Hutterer <peter.hutterer@...-t.net>, seobrien@...omium.org,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] HID: hid-input: avoid splitting keyboard, system and
 consumer controls

A typical USB keyboard usually splits its keys into several reports:

- one for the basic alphanumeric keys, modifier keys, F<n> keys, six pack
  keys and keypad. This report's application is normally listed as
  GenericDesktop.Keyboard
- a GenericDesktop.SystemControl report for the system control keys, such
  as power and sleep
- Consumer.ConsumerControl report for multimedia (forward, rewind,
  play/pause, mute, etc) and other extended keys.
- additional output, vendor specific, and feature reports

Splitting each report into a separate input device is wasteful and even
hurts userspace as it makes it harder to determine the true capabilities
(set of available keys) of a keyboard, so let's adjust application
matching to merge system control and consumer control reports with
keyboard report, if one has already been processed.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
---
 drivers/hid/hid-input.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/hid/hid-input.c b/drivers/hid/hid-input.c
index f797659cb9d9..df45d8d07dc2 100644
--- a/drivers/hid/hid-input.c
+++ b/drivers/hid/hid-input.c
@@ -1851,6 +1851,16 @@ static struct hid_input *hidinput_match_application(struct hid_report *report)
 	list_for_each_entry(hidinput, &hid->inputs, list) {
 		if (hidinput->application == report->application)
 			return hidinput;
+
+		/*
+		 * Keep SystemControl and ConsumerControl applications together
+		 * with the main keyboard, if present.
+		 */
+		if ((report->application == HID_GD_SYSTEM_CONTROL ||
+		     report->application == HID_CP_CONSUMER_CONTROL) &&
+		    hidinput->application == HID_GD_KEYBOARD) {
+			return hidinput;
+		}
 	}
 
 	return NULL;
-- 
2.30.0.284.gd98b1dd5eaa7-goog


-- 
Dmitry