My issue with the LED subsystem is that to my knowledge, the only thing
that it currently exposes is an opaque brightness value that has plenty
of different meanings depending on what is actually being exposed. It
would need to be overhauled to support the usecase at hand, which would
be a lot more work than just applying this patch, on top of all the
other problems already mentioned with finding and using the sysfs LED
interface.
With this change all the gamepad drivers could easily plumb through
their device-specific way of exposing player IDs, and a userspace
component could easily ensure consistency between logical player IDs and
their LEDs.
If such a thing was attempted currently with gamepads that are wired up
to LED classes, the userspace component would need to have special
knowledge of each driver to be able to know which special brightness
value to set to get player N to light up on the controller. This isn't
solvable without significantly expanding the interface to the LED subsystem.
Michael, I assume such a userspace component is what you're shooting for
with this work?
In SteamOS the individual gamepad drivers are modified to automatically
apply player IDs from the joydev device IDs, which in turn are the
logical game controller IDs that are exposed by libraries such as SDL to
games and as such are reflected through their UI.
This was deemed too ad-hoc to be upstreamable and your patch seems like
the right first step towards a cleaner, albeit slightly more complex
solution. Trying to leverage the LED system seems a lot more complex,
without adding any value to this solution.
Thanks,
- Pierre-Loup
On 09/15/2014 09:06 PM, Michael Wright wrote:
On Mon, Sep 15, 2014 at 7:00 PM, <simon@xxxxxxxxxxxxx> wrote:
One problem that exists is that many HID devices don't have an (embedded)
serial number, so identification can be confused if you have more that one
identical device.
That's a pretty serious problem since this is explicitly for multiple
gamepads connected to the same device, which will most likely be all
the same type.
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