[PATCH] Input: increase max button number to 0x3ff

[PATCH] Input: increase max button number to 0x3ff

[Tomasz Pakuła]

Maximum number of buttons is limited to 0x2ff. This makes it so game
controllers like joysticks, racing wheelbases etc. are limited to 80
buttons.

A lot of input devices for flight simulators and racing simulators take
full advantage of Windows' input API limitation of 128 buttons and,
in turn, some of their buttons simply don't show up under linux. While
normally I'd say doing something just becuase other OS does, doesn't
seem like enough of a reason, Linux became quite a viable gaming
platform in the recent years so this makes it so it supports all the HID
peripherals without fuss and confusion (there aren't any dmesg errors if
HID device exceeds the 0x2ff button id).

I'm a part of linux simracing community and we encoutered this issue
with Moza Racing wheelbases, as they use top of the range for things
like h-pattern shifters, sequential shifters. These accessories simply
don't work, be it connected through the wheelbase or directly with USB.

Upcoming Moza Flight Sim devices will face the same issue, and there were
Saitek/Logitech/Honeycomb and custom-made products that also have more
then 80 buttons.

0x2ff was already sort of an arbitrary number, so I'm increasing it to
0x3ff to keep the value straight-forward.

Change has been verified on my Moza Racing R9 wheelbase + Moza racing
sequential shifter (it uses buttons 112-117).

Signed-off-by: Tomasz Pakuła <tomasz.pakula.oficjalny@gmail.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 4338b1b4ac44..c2cb3a2d0dc7 100644
--- a/include/linux/mod_devicetable.h
+++ b/include/linux/mod_devicetable.h
@@ -333,7 +333,7 @@ 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		0x3ff
 #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 a4206723f503..a8eace215b54 100644
--- a/include/uapi/linux/input-event-codes.h
+++ b/include/uapi/linux/input-event-codes.h
@@ -808,7 +808,7 @@
 
 /* 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			0x3ff
 #define KEY_CNT			(KEY_MAX+1)
 
 /*
-- 
2.45.2

Re: [PATCH] Input: increase max button number to 0x3ff

[Michał Kopeć]

Do you have any guess as to where this old value came from?
It's weird that this wasn't caught already.

CCing some more maintainers to get some more eyes on this, I hope that's okay.

Re: [PATCH] Input: increase max button number to 0x3ff

[Benjamin Tissoires]

On Jul 05 2024, Michał Kopeć wrote:
> Do you have any guess as to where this old value came from?
> It's weird that this wasn't caught already.
> 
> CCing some more maintainers to get some more eyes on this, I hope that's okay.
> 

Dmitry will probably know better but I've made the forensic, and that
value came from 03bac96fae0e ("Input: expand keycode space").
The value seemed arbitrary, but we do try to keep it low because there
are a lot of static arrays in the kernel which are using KEY_MAX as a
size.

Also, it might be worth double checking, but last time we tried
something similar on EV_ABS range and it fell short because of the ioctl
that couldn't work properly IIRC. I don't seem to find the ML
discussion, but it would be interesting for someone to un-earth it and
see if we are facing similar issues.

Cheers,
Benjamin

Re: [PATCH] Input: increase max button number to 0x3ff

[Tomasz Pakuła]

This would be be really helpful in making linux even better for gaming.
It's weird that Valve didn't catch this already :)

Do you have any guess as to where this old value came from?

Re: [PATCH] Input: increase max button number to 0x3ff

[Tomasz Pakuła]

I tested this on my two machines and everythig worked perfectly. evtest
was able to detect all the buttons advertised by the wheelbase. I couldn't
test it in games running through proton as SDL has to be recompiled with
this patch applied and updated (SDL relies on this constant)

If this is a pressing matter, I could resubmit this patch but with the value
increased to 0x333 instead of 0x3ff to cut down on teh mentioned array sizing.
0x333 wuld still include support for 128 buttons. 0x3ff would be more
future-proof, but we can always adjust this value later.