Hi all,
Am 26.03.24 um 16:39 schrieb Benjamin Tissoires:
On Mar 26 2024, Werner Sembach wrote:
Hi all,
Am 25.03.24 um 19:30 schrieb Hans de Goede:
[snip]
If the kernel already handles the custom protocol into generic HID, the
work for userspace is not too hard because they can deal with a known
protocol and can be cross-platform in their implementation.
I'm mentioning that cross-platform because SDL used to rely on the
input, LEDs, and other Linux peculiarities and eventually fell back on
using hidraw only because it's way more easier that way.
The other advantage of LampArray is that according to Microsoft's
document, new devices are going to support it out of the box, so they'll
be supported out of the box directly.
Most of the time my stance is "do not add new kernel API, you'll regret
it later". So in that case, given that we have a formally approved
standard, I would suggest to use it, and consider it your API.
The only new UAPI would be the use_leds_uapi switch to turn on/off the backwards compatibility.
I have my reserves with such a kill switch (see below).
Actually we don't even need that. Typically there is a single HID
driver handling both keys and the backlight, so userspace cannot
just unbind the HID driver since then the keys stop working.
I don't think Werner meant unbinding the HID driver, just a toggle to
enable/disable the basic HID core processing of LampArray.
But with a virtual LampArray HID device the only functionality
for an in kernel HID driver would be to export a basic keyboard
backlight control interface for simple non per key backlight control
to integrate nicely with e.g. GNOME's backlight control.
Don't forget that in the future there will be devices that natively support
LampArray in their firmware, so for them it is the same device.
Yeah, the generic LampArray support will not be able to differentiate
"emulated" devices from native ones.
Regards,
Werner
And then when OpenRGB wants to take over it can just unbind the HID
driver from the HID device using existing mechanisms for that.
Again no, it'll be too unpredicted.
Hmm, I wonder if that will not also kill hidraw support though ...
I guess getting hidraw support back might require then also manually
binding the default HID input driver. Bentiss any input on this?
To be able to talk over hidraw you need a driver to be bound, yes. But I
had the impression that LampArray would be supported by default in
hid-input.c, thus making this hard to remove. Having a separate driver
will work, but as soon as the LampArray device will also export a
multitouch touchpad, we are screwed and will have to make a choice
between LampArray and touch...
Background info: as discussed earlier in the thread Werner would like
to have a basic driver registering a /sys/class/leds/foo::kbd_backlight/
device, since those are automatically supported by GNOME (and others)
and will give basic kbd backlight brightness control in the desktop
environment. This could be a simple HID driver for
the hid_allocate_device()-ed virtual HID device, but userspace needs
to be able to move that out of the way when it wants to take over
full control of the per key lighting.
Do we really need to entirely unregister the led class device? Can't we
snoop on the commands and get some "mean value"?
Regards,
Hans
The control flow for the whole system would look something like this:
- System boots
- Kernel driver initializes keyboard (maybe stops rainbowpuke boot effects, sets brightness to a default value, or initializes a solid color)
- systemd-backlight restores last keyboard backlight brightness
- UPower sees sysfs leds entry and exposes it to DBus for DEs to do keyboard brightness handling
- If the user wants more control they (auto-)start OpenRGB
- OpenRGB disables sysfs leds entry via use_leds_uapi to prevent double control of the same device by UPower
- OpenRGB directly interacts with hidraw device via LampArray API to give fine granular control of the backlight
- When OpenRGB closes it should reenable the sysfs leds entry
That's where your plan falls short: if OpenRGB crashes, or is killed it
will not reset that bit.
Next question: is OpenRGB supposed to keep the hidraw node opened all
the time or not?
TBH I didn't look at the OpenRGB code yet and LampArray there is currently only
planned. I somewhat hope that until the kernel driver is ready someone else
already picked up implementing LampArray in OpenRGB.
If it has to keep it open, we should be able to come up with a somewhat
similar hack that we have with hid-steam: when the hidraw node is
opened, we disable the kernel processing of LampArray. When the node is
closed, we re-enable it.
But that also means we have to distinguish steam/SDL from OpenRGB...
My first thought here also: What is if something else is reading hidraw devices?
Especially for hidraw devices that are not just LampArray.
I just carefully read the LampArray spec. And it's simpler than what
I expected. But the thing that caught my attention was that it's
mentioned that there is no way for the host to query the current
color/illumination of the LEDs when the mode is set to
AutonomousMode=false. Which means that the kernel should be able to
snoop into any commands sent from OpenRGB to the device, compute a mean
value and update its internal state.
Basically all we need is the "toggle" to put the led class in read-only
mode while OpenRGB kicks in. Maybe given that we are about to snoop on
the commands sent, we can detect that there is a LampArray command
emitted, attach this information to the struct file * in hidraw, and
then re-enable rw when that user closes the hidraw node.
I think a read-only mode is not part of the current led class UAPI. Also I don't
want to associate AutonomousMode=true with led class is used.
AutonomousMode=true could for example mean that it is controlled via keyboard
shortcuts that are directly handled in the keyboard firmware, aka a case where
you want neither OpenRGB nor led class make any writes to the keyboard.
Or AutonomousMode=true could mean that on a device that implements both a
LampArray interface as well as a proprietary legacy interface is currently
controlled via the proprietary legacy interface (a lot of which are supported by
OpenRGB).
Regards,
Werner
Cheers,
Benjamin
- System shutdown
- Since OpenRGB reenables the sysfs leds entry, systemd-backlight can correctly store a brightness value for next boot
Regards,
Werner
Side note to self: I really need to resurrect the hidraw revoke series
so we could export those hidraw node to userspace with uaccess through
logind...
Cheers,
Benjamin
