I think we need a decision about what needs to be done in kernel and
what is better handled in user-space. I've walked through the Corsair
Vengeance K90 driver (hid-corsair.c) and I must say, I'm not really
happy about the desicions made in the design. In my opinion, we should
only do essential stuff in kernel space and do the rest in user-space.
To be more precise about hid-corsair.c (and possibly future gaming
keyboard implementations):
1. We should not handle profile switching and exposing a sysfs ABI for
profile-number in kernel-space. This has no advantage over keeping track
of profiles in user-space. We need to use user-space programs anyway in
order to handle macros and profile-sensitive key-handling. Using a
keyboard specific ABI for parsing the profile just adds complexity to
kernel- and user-space.
2. We should not map false keycodes to keys. hid-corsair.c is using
BTN_TRIGGER_HAPPY[N] - this is a huge design flaw in my opinion.
Eventhough this might get the job done, I'm questioning the design
decision. First of all, we're generally talking about KEYs on a
keyboard, not BTNs. Second, they are not TRIGGERs. Third, they are not
HAPPY. Also, BTN_TRIGGER_HAPPY[N] is only specified for up to 40 extra
keys. What do we do with gaming keyboards, which offer more? The
Microsoft Sidewinder X6 has 33 non-standard extra keys for example
(agreed, it's less than 40, but still near the maximum). Do we really
need to map random linux/input.h keycodes to non-standard keys?
I think mapping linux/input.h keycodes to non-standard keys has only one
reason: to keep things simple with X11. As Clement mentioned, keycodes
above 256 don't work with X11. However, this should not be a reason to
hack workarounds into kernel. We can use hidraw / hiddev in user-space
instead to catch those events and map them accordingly to our needs
(they are designed to be fully programmable keys after all). This adds
complexity in user-space, but also adds flexibility and we don't need to
break / workaround any HID stuff.
3. We should either have common ABI for gaming keyboards or we shouldn't
have them at all (or just in very special cases). This just adds
complexity in kernel- and user-space, as lots of keyboards need to be
handled their own way. Gaming keyboards have things in common, like
LEDs. Creating an ABI for setting extra LEDs is totally legit, but we
should define standards, so user-space applications can rely on
something. Most keyboards have multiple profile LEDs, 1 recording LED,
sometimes 1 gaming mode LED (disabling Windows key) and sometimes
keyboard backlight is also adjustable.
We could define a common ABI for them:
- read-only profile_led_count (or profile_led_max): parse number of
profile_leds
- rw profile_led_[N]: setting and parsing profile_led_[N] status, 0 and 1
- rw recording_led: setting and parsing recording_led status, 0 and 1
- rw gaming_led: setting and parsing gaming_led status, 0 and 1
- read-only backlight_max: parse maximum brightness
- rw backlight: setting and parsing backlight intensity, 0 - backlight_max
Exposing a read-write interface for switching HW / SW mode is also a
legit use-case for ABI.
A major drawback of ABI (and user-space programs depending on it): we
cannot respond fast enough to new devices, as people need to wait
several months / years for the updated kernel versions or run a patched
kernel (including all the drawbacks associated with using a custom
kernel for the average user).
The kernel's role would be creating an interface to interact with the
keyboard's extras and it's up to the user-space, how to make use of them
(e.g. profile-switching macro tool using LEDs for active profile number,
or custom script using them in a blinking pattern for incoming E-Mails).
Now about the Logitech G710+. Things, that need and should be handled in
kernel space (in my opinion):
1. Bugs. Thanks to Jimmy Berry, there is already a G710+ bugfix applied
to 4.4 (http://www.spinics.net/lists/linux-input/msg42186.html). There
are no other bugs for the G710+ I'm aware of.
2. The Logitech G710+ is a composite device: interface #1 is used for G1
- G6 keys + usual standard keyboard. Please note, that the G1 - G6 keys
are outputting KEY_1 - KEY_6. Interface #2 is used for M1 - M3, MR key
(macro recording and profile switching / LEDs) and also the G1 - G6 keys
(outputting non-standard HID events!). As you can see, G1 - G6 keys are
double mapped for 2 devices. In case, an operating system doesn't
recognize G1 - G6 keys on interface #2, we're simply getting KEY_1 -
KEY6 from interface #1. The Windows Logitech driver is sending out a
specific packet, so the G1 - G6 keys on interface #1 get completely
disabled (maybe other changes aswell, I don't know). This is a perfect
use case for kernel-space.
Sorry for the wall of text.
Cheers,
Tolga
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