Re: [PATCH 0/6] HID: sony: More Sony controller fixes and improvements.

[Frank Praznik <frank.praznik@oh.rr.com>]

On 3/1/2014 08:53, Antonio Ospite wrote:
> Hi Frank,
>
> On Fri, 28 Feb 2014 22:58:55 -0500
> Frank Praznik <frank.praznik@oh.rr.com> wrote:
>
>> This set consists of one bugfix, two mostly cosmetic changes and three larger
>> patches for the LED subsystem.
>>
>> Patch #4 adds hardware blink support to the controller LEDs.  Values from 0 to
>> 2.5 seconds are supported by the hardware.  The Sixaxis can set all of the LEDs
>> individually, but the DualShock 4 only has one global setting for the entire
>> light bar so only the value from the most recently set LED is used.
>>
> Adding this is OK, as it adds access to something supported by the
> hardware.
>
>> Patch #5 adds an LED trigger that reports the controller battery status via the
>> registered LEDs.  The LEDs will flash if the controller is charging or if the
>> battery is low, and remain solid otherwise.
>>
> This kind of logic _may_ belong to userspace. More comments in the
> actual patch.
Functionally this trigger is no different from the ones registered by 
the power supply system when a battery is registered, aside from the 
specific conditions under which the LED blinks.  I can understand the 
reservations about setting it as the default, but at the same time it's 
a trigger which can be easily disabled on the controller LEDs or be used 
to control other LED devices if the user desires it.

If this is something best kept out of kernel code though, that's fine.
>
>> Patch #6 initializes the LEDs to a default value of LED 1 on the Sixaxis and
>> blue on the DualShock 4 so there is some indication that the controller is
>> powered on and connected in the case of Bluetooth.  The code can be used to set
>> the LEDs based on the device number, but I'm not sure how to actually retrieve
>> the controller number from the system.  I saw the xpad patches posted a few
>> weeks ago where the minor number of the joydev device was used, but I'm under
>> the impression that doing that is not ideal.  Any suggestions?
> Setting the controller number is done by the bluez sixaxis plugin[1]
> (in bluez 5.x) following the X in /dev/input/jsX, this covers the
> case of a mixed-joypad scenario, IMHO it makes sense that the
> controller number matches the joystick device number.
> Imagine js0->Sixaxis1, js1->wiimote, js2->Sixaxis2, I think it make
> sense to have the LEDs on Sixaxis2 say "controller 3", not 2.
>
> This has been done in userspace with libudev for 2 reasons:
>    1. the hid drivers should not have knowledge of the joystick layer;
>    2. kernel drivers should be as simple as possible, and try to just
>       exposing hardware functionalities but with as less "business logic"
>       as possible in them.
>
> The current implementation in the bluez plugin uses hidraw, but support
> for the sysfs led class could be added in order to avoid conflicts with
> the rumble; IIRC, currently, setting rumble values could override the
> LED settings done via hidraw, because the LEDs state is not tracked in
> the latter case.
>
> Ciao,
>     Antonio
>
> [1]
> http://git.kernel.org/cgit/bluetooth/bluez.git/tree/plugins/sixaxis.c
>
This can be done in the driver. See 
https://www.mail-archive.com/linux-input@vger.kernel.org/msg08103.html

It seems that the main problem with that patch is that modern systems 
shouldn't be relying on joydev for this functionality.  I'd like to know 
what David Herrmann and Greg Kroah-Hartman came up with regarding the 
solution mentioned in the reply as it would be nice to be able to set 
the LEDs to the proper default values in the driver without needing to 
rely on an external daemon. Setting the defaults in the driver doesn't 
interfere with setting custom values after the device is initialized, so 
there are no issues if the user wants to use a custom LED daemon.

As far as the behavior of patch #6 (setting the LEDs to the same number 
or color on every connected device just to indicate that the controller 
is turned on), the xpad and wiimote drivers both initialize the LEDs to 
some default value where at least one is on to indicate that the 
controller is powered on and connected to the system.  The xpad driver 
increments an atomic counter for assigning values as controllers are 
connected and the wiimote always sets LED #1 to on.  Not ideal, but it 
serves it's purpose.

Personally I don't like the idea of relying on a BlueZ plugin to set the 
controller LED values as it seems to bring a lot of issues with it: 
users may not have BlueZ installed or enabled, some distros still use an 
old version, the plugin relies on joydev to get the device number which 
is why the patch I linked was NAKed, the current plugin implementation 
doesn't set them via sysfs so the setting will be lost if force-feedback 
is used and the plugin could conflict with other user-installed daemons 
that set the LEDs (unless udev guarantees a notification order?).  In 
the latter scenario, the user could disable the plugin, but then you 
lose the Sixaxis pairing functionality that it provides.  I also have to 
question as to why BlueZ is considered an appropriate place to set 
controller LEDs, particularly on controllers that aren't connected via 
Bluetooth.