linux-kernel - [PATCH] Input: expand keycode space

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Message-ID: <CACa7zymSNJJy1MJeNzzH22MAOH4=fxu_GJcdaY5JRqM3A_jkGA@mail.gmail.com>
Date:   Sun, 3 Dec 2023 20:50:19 +0800
From:   Wei Shuai <cpuwolf@...il.com>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        "open list:INPUT (KEYBOARD, MOUSE, JOYSTICK, TOUCHSCREEN)..." 
        <linux-input@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: [PATCH] Input: expand keycode space

Dear Dmitry Torokhov,

Today I found out that in 2008, you have expanded the number of
potential key codes from 512 to 768.

I request to expand keycode space again, from 0x2ff to 0x4ff. I have
tested this patch on Ubuntu Kernel, it works well with a USB HID
joystick that has more than 80 keys.

Story back to I found Linux kernel has max USB HID joystick buttons up
to 80, no more.  But Windows OS and Mac OS have no such limitations.

I have a USB HID joystick device, which has 104 buttons, larger than 80.

I did a lot of google search, but nothing I got. then I have to look
at Kernel source, to find out where this number max 80 comes from

Eventually, I found the final limitation

#define BTN_JOYSTICK 0x120
#define BTN_DEAD 0x12f
#define BTN_TRIGGER_HAPPY 0x2c0
#define KEY_MAX 0x2ff

include/uapi/linux/input-event-codes.h

according to function hidinput_configure_usage() in file drivers/hid/hid-input.c

the USB joystick button mapping is not a continuous space, generally speak
the mapping space is from

BTN_JOYSTICK~BTN_DEAD 0x120~0x12f=0x10
BTN_TRIGGER_HAPPY~KEY_MAX 0x2c0~0x2ff=40

0x10+0x40=0x60=80

and finally, I got the max limitation of 80 for joystick keys.

This patch is about expanding keycode space from 0x2ff to 0x4ff. I
expect this patch won't go with ease, because it affects user space
application definition as well. I believe sooner or later Linux kernel
will face keycode is not enough


Signed-off-by: Wei Shuai <cpuwolf@...il.com>
---
 include/linux/mod_devicetable.h        | 2 +-
 include/uapi/linux/input-event-codes.h | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/mod_devicetable.h b/include/linux/mod_devicetable.h
index 8d764aab29de..35eb59ae1f19 100644
--- a/include/linux/mod_devicetable.h
+++ b/include/linux/mod_devicetable.h
@@ -311,7 +311,7 @@ struct pcmcia_device_id {
 /* Input */
 #define INPUT_DEVICE_ID_EV_MAX         0x1f
 #define INPUT_DEVICE_ID_KEY_MIN_INTERESTING    0x71
-#define INPUT_DEVICE_ID_KEY_MAX                0x2ff
+#define INPUT_DEVICE_ID_KEY_MAX                0x4ff
 #define INPUT_DEVICE_ID_REL_MAX                0x0f
 #define INPUT_DEVICE_ID_ABS_MAX                0x3f
 #define INPUT_DEVICE_ID_MSC_MAX                0x07
diff --git a/include/uapi/linux/input-event-codes.h
b/include/uapi/linux/input-event-codes.h
index b6a835d37826..ad1b9bed3828 100644
--- a/include/uapi/linux/input-event-codes.h
+++ b/include/uapi/linux/input-event-codes.h
@@ -774,7 +774,7 @@

 /* We avoid low common keys in module aliases so they don't get huge. */
 #define KEY_MIN_INTERESTING    KEY_MUTE
-#define KEY_MAX                        0x2ff
+#define KEY_MAX                        0x4ff
 #define KEY_CNT                        (KEY_MAX+1)

 /*
--
2.17.1