linux-kernel - Re: [Patch-V2 1/6] INPUT: xpad: Add minimal support for Logitech G920 Wheel

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Message-ID: <hhnu52.o0fhzs.2yy6b9-qmf@smtp.devoid-pointer.net>
Date:	Mon, 4 Jan 2016 12:43:02 +0000
From:	madcatxster@...oid-pointer.net
To:	benjamin.tissoires@...hat.com
Cc:	jikos@...nel.org, simon@...gewell.org, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org, Edwin@...ds.nl, elias.vds@...il.com,
	dmitry.torokhov@...il.com
Subject: Re: [Patch-V2 1/6] INPUT: xpad: Add minimal support for Logitech
 G920 Wheel



On Mon Jan 4 10:55:24 2016 GMT+0100, Benjamin Tissoires wrote:
> On Dec 10 2015 or thereabouts, Dmitry Torokhov wrote:
> > On Thu, Dec 10, 2015 at 9:08 AM, Benjamin Tissoires
> > <benjamin.tissoires@...hat.com> wrote:
> > > On Dec 09 2015 or thereabouts, Dmitry Torokhov wrote:
> > >> On Wed, Dec 9, 2015 at 5:23 PM, Dmitry Torokhov
> > >> <dmitry.torokhov@...il.com> wrote:
> > >> > On Thu, Nov 19, 2015 at 10:31 AM, Dmitry Torokhov
> > >> > <dmitry.torokhov@...il.com> wrote:
> > >> >> On Thu, Nov 19, 2015 at 02:50:51PM +0100, Jiri Kosina wrote:
> > >> >>> On Thu, 12 Nov 2015, Simon Wood wrote:
> > >> >>>
> > >> >>> > When plugged in the Logitech G920 wheel starts with USBID 046d:c261
> > >> >>> > and behaviors as a vendor specific class. If a 'magic' byte sequence
> > >> >>> > is sent the wheel will detach and reconnect as a HID device with the
> > >> >>> > USBID 046d:c262.
> > >> >>> >
> > >> >>> > Signed-off-by: Simon Wood <simon@...gewell.org>
> > >> >>>
> > >> >>> Adding Dmitry to CC.
> > >> >>>
> > >> >>> Dmitry, I am planning to take this through my tree together with the rest
> > >> >>> of the actual HID support for that device if you Ack this.
> > >> >>
> > >> >> Hmm, I have an incoming series for xbox that night clash with this... If
> > >> >> you'll put it in a clean branch off 4.3 I'd pull it and then get more
> > >> >> changes on top.
> > >> >>
> > >> >> Can we also change the subject as it is not about adding a minimal
> > >> >> support. Something like "Input: xpad - switch Logitech G920 Wheel into
> > >> >> HID mode"
> > >> >>
> > >> >> Otherwise:
> > >> >>
> > >> >> Acked-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
> > >> >
> > >> > Hmm, looking sat this some more why are we waiting to switch device
> > >> > mode until after userspace opens input device instead of when we are
> > >> > executing driver probe()?
> > >> >
> > >>
> > >> Actually, thinking about it even more, why do we want to have this in
> > >> xpad.c? Have HID module handle both IDs and switch to HID mode if we
> > >> want HID to handle this device. I think we should revert/drop this
> > >> patch.
> > >>
> > >
> > > Hi Dmitry,
> > 
> > Hi Benjamin,
> > 
> > >
> > > IIRC, last time I saw an XBox-like controller, it doesn't register as a
> > > HID device at all. SO I think It will be hard to switch it into the HID
> > > mode from HID directly.
> > > Simon, can you confirm that the device does not contains any references
> > > to HID while in the XBox mode (lsusb -v should give enough information).
> > >
> > > Switching the device during probe in xpad.c makes a lot of sense
> > > however.
> > 
> > It makes as much sense doing it in xpad as doing it from a random USB
> > network driver. I mean the only reason we are doing it from xpad is
> > because of name and the fat that it has usb_driver structure. Nobody
> > stops you from creating a tiny USB stub driver in hid portion that
> > would probe the "non-hid" device and switch it over to hid.
> > 
> 
> Jiri, I *think* this commit still is in your next pull request for
> Linus. We might want to drop it before it hits Linus' tree.
> 
> We can still keep the HID work in place even if the device is not
> switched into the HID protocol at plug.
> 
> Simon, do you mind looking into Dmitry's suggestion of having a clean,
> small usb device which loads itself when the G920 is plugged in and
> switches it immediately into the HID mode?
> 
> Cheers,
> Benjamin
> 

Hi guys,

since I feel pretty bad for not contributing to the project (too much PhD stuff) I'd gladly look into the USB stub driver is Simon is too buys or otherwise unable to do it himself. If I understand the issue the idea is to have a simple module that would pick up a device that at first appears as a generic USB device, do the necessary initialization and let the device-specific driver take over from there?

Michal