(sorry resend because thunderbird made it a html mail)
Hi,
Am 30.09.24 um 19:06 schrieb Benjamin Tissoires:
On Sep 30 2024, Werner Sembach wrote:
[...]
Thinking about it, maybe it's not to bad that it only changes once udev is
ready, like this udev could decide if leds should be used or if it should
directly be passed to OpenRGB for example, giving at least some consistency
only changing once: i.e. firmware -> OpenRGB setting and not firmware->leds
setting->OpenRGB setting.
That would work if OpenRGB gets to ship the LampArray bpf object (not
saying that it should). Because if OpenRGB is not installed, you'll get
a led class device, and if/when OpenRGB is installed, full LampArray
would be presented.
The idea in my head is still that there is some kind of sysfs switch to
enable/disable leds.
My idea is then that a udev rule shipped with OpenRGB sets this switch to
disable before loading the BPF driver so leds never get initialized for the
final LampArray device.
But anyway, BPF allows to dynamically change the behaviour of the
device, so that's IMO one bonus point of it.
FWIW, the use of BPF only allows you to not corner yourself. If you
failed at your LampArray implementation, you'll have to deal with it
forever-ish. So it's perfectly sensible to use BPF as an intermediate step
where you develop both userspace and kernel space and then convert back
the BPF into a proper HID driver.
I don't really see this point: The LampArray API is defined by the HID Usage
Table and the report descriptor, so there is not API to mess up and
everything else has to be parsed dynamically by userspace anyway, so it can
easily be changed and userspace just adopts automatically.
And for this case the proper HID driver is already ready.
Yeah, except we don't have the fallback LED class. If you are confident
enough with your implementation, then maybe yes we can include it as a
driver from day one, but that looks like looking for troubles from my
point of view.
To be on the safe side that we don't talk about different things: My current
plan is that the leds subsystem builds on top of the LampArray implementation.
Like this the leds part has to be only implemented once for all LampArray
devices be it emulated via a driver or native via firmware in the device itself.
And I feel confident that the UAPI should be that the userspace gets a hidraw
device with a LampArray HID descriptor, and every thing else is, by the HID
spec, dynamic anyway so I can still change my mind in implementation specifics
there, can't I?
After a second look at the LampArray code here... Aren't you forgetting
the to/from CPU conversions in case you are on a little endian system?
Since this driver is for built in keyboards of x86 notebooks it isn't required
or is it?
So the only point for me currently is: Is it ok to have key position/usage
description tables in the kernel driver or not?
good question :)
I would say, probably not in the WMI driver itself. I would rather have
a hid-tuxedo.c HID driver that does that. But even there, we already had
Linus complaining once regarding the report descriptors we sometimes
insert in drivers, which are looking like opaque blobs. So it might not be
the best either.
Isn't tuxedo_nb04_wmi_ab_virtual_lamp_array.c not something like hid-tuxedo.c?
or should it be a separate file with just the arrays?
Sorry I don't have a clear yes/no answer.
Hm... Well if it's no problem I would keep the current implementation with minor
adjustments because, like i described above, I don't see a benefit now that this
already works to rewrite it in BPF again.
If it is a problem then i don't see another way then to rewrite it in BPF.
Note: For future devices there might be more keyboard layouts added, basically
every time the chassis form factor changes.
Cheers,
Benjamin
To sum up the architechture (not mutally exclusive technically)
/- leds
WMI <- WMI to LampArray Kernel driver <-switch-|
\- OpenRGB
/- leds
WMI <- WMI to Custom HID Kernel driver <- Custom HID to LampArray BPF
driver<-switch-|
\- OpenRGB
With the "switch" and "leds" implemented in hid core, automatically initialized
every time a LampArray device pops up (regardless if it is from native firmware,
a bpf driver or a kernel driver)
Writing this down I think it was never decided how the switch should look like:
It should not be a sysfs attribute of the leds device as the leds device should
disappear when the switch is set away from it, but should it be a sysfs variable
of the hid device? This would mean that hid core needs to add that switch
variable to every hid device having a LampArray section in the descriptor.
Being able to develop a kernel driver without having to reboot and
being sure you won't crash your kernel is a game changer ;)
Cheers,
Benjamin
Best regards and sorry for the many questions,
Werner Sembach
PS: on a side node: How does hid core handle HID devices with a broken HID
implementation fixed by bpf, if bpf is loaded after hid-core? Does the hid
device get reinitialized by hid core once the bpf driver got loaded? If yes, is
there a way to avoid side effects by this double initialization or is there a
way to avoid this double initialization, like marking the device id as broken so
that hid core- does not initialize it unless it's fixed by bpf?
