On Tue, 16 Feb 2021 18:29:46 +0100
Benjamin Tissoires <benjamin.tissoires@xxxxxxxxxx> wrote:
> > So all HIDs can be uniqely determined via this atomic_inc_return(&id),
> > but it is only stored in string form as part of device name.
>
> Yes and no. This atomic_inc is only used to allow a sysfs tree,
> because you can have several HID devices below the same USB, I2C or
> UHID physical device. From the userspace, no-one cares about that ID,
> because all HID devices are exported as input, IIO or hidraw nodes.
>
> So using this "id" would not allow for a direct mapping HID device ->
> sysfs entry because users will still have to walk through the tree to
> find out which is which.
So you are saying that the fact that userspace cannot take the number
from "hidN" string and simply do a lookup /sys/bus/hid/devices/hidN is
the problem here.
This is not a problem in my opinion, because userspace can simply
access the parent HID device via /sys/class/leds/hidN:color:func/parent.
In fact we did something similar for LEDs connected to ethernet PHYs.
To summarize:
- ethernet PHYs are identified by long, sometimes crazy strings like
d0032004.mdio-mii:01
or even
/soc/internal-regs@d0000000/mdio@32004/switch0@10/mdio:08
- for the purposes of having a sane devicename part in LED names, I
sent this patch
https://www.mail-archive.com/linux-kernel@xxxxxxxxxxxxxxx/msg2301470.html
which adds a simple incrementing integer ID to each PHY device.
(The code is not in upstream yet because there is other work needed
and because I decided that some functionality has to be available
via a different mechanism, but this part is complete and reviewed.)
> An actual one-to-one mapping would using 'hidrawX' because there is a
> one-to-one mapping between /dev/hidrawX for HID devices. However, this
> means that we consider the bus to be hidraw which is plain wrong too.
>
> The unique ID of HID devices (in /sys/bus/hid/devices) is in the form
> `BUS:VID:PID.XXXX`. I understand the need to not have colons, so could
> we standardize LEDs on the HID subsystem to be named
> `hid-bus_vid_pid_xxxx:color:fun(-n)?`? That would allow a mapping
> between the LED and the sysfs, and would also allow users to quickly
> filter out the playstation ones.
As I wrote in other e-mail some minutes ago, this just means that we
need to wait for other people's opinions. Please do not send this
pull-request with the LED patches until this is resolved.
Marek
