Date:   Tue, 13 Sep 2016 15:58:00 +0200
From:   Benjamin Tissoires <benjamin.tissoires@...hat.com>
To:     Michel Hermier <michel.hermier@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-input@...r.kernel.org,
        Jiri Kosina <jikos@...nel.org>,
        Jason Gerecke <killertofu@...il.com>
Subject: Re: [PATCH 1/2] HID: input: ignore System Control application usages
 if not System Controls

On Sep 13 2016 or thereabouts, Michel Hermier wrote:
> Hi,
> 
> Le 13 sept. 2016 11:54 AM, "Benjamin Tissoires" <
> benjamin.tissoires@...hat.com> a écrit :
> >
> > Microsoft is reusing its report descriptor again and again, and part of it
> > looks like this:
> >
> > 0x05, 0x01,                    // Usage Page (Generic Desktop)        299
> > 0x09, 0x80,                    // Usage (System Control)              301
> > 0xa1, 0x01,                    // Collection (Application)            303
> > 0x85, 0x03,                    //  Report ID (3)                      305
> > 0x19, 0x00,                    //  Usage Minimum (0)                  307
> > 0x29, 0xff,                    //  Usage Maximum (255)                309
> > 0x15, 0x00,                    //  Logical Minimum (0)                311
> > 0x26, 0xff, 0x00,              //  Logical Maximum (255)              313
> > 0x81, 0x00,                    //  Input (Data,Arr,Abs)               316
> > 0xc0,                          // End Collection                      318
> >
> > While there is nothing wrong in term of processing, we do however blindly
> > map the full usage range (it's an array) from 0x00 to 0xff, which creates
> > some interesting axis, like ABS_X|Y, and a bunch of ABS_MISC + n.
> >
> > While libinput and other stacks don't care that much (we can detect them),
> > joydev is very happy and attaches itself to the mouse or keyboard.
> >
> > The problem is that joydev now handles the device as a joystick, but given
> > that we have a HID array, it sets all the ABS_* values to 0. And in its
> > world, 0 means -32767 (minimum value), which sends spurious events to
> games
> > (think Steam).
> >
> > It looks like hid-microsoft tries to tackle the very same problem with its
> > .report_fixup callback. But fixing the report descriptor is an endless
> task
> > and is quite obfuscated.
> 
> Do you plan to remove those various fixup in a later patch series, or do
> you have other plans?

Well, I don't have the affected hardware on hid-microsoft, so I was planing
on just leaving the code as it is.

If you have some and can test/verify, then do not hesitate to remove
those quirks.

> 
> >
> > So take the hammer, and decide that if the application is meant to be
> > System Control, any other usage not in the System Control range should
> > be ignored.
> 
> To be on a safe side, shouldn't there be a flag to bypass that change in
> case it makes some situations worse? (Thought I agree we should be pretty
> safe here)

Well, we are safe unless Hardware makers start doing weird things. But
hardware makers always like doing weird things.

I think I am more willing to try fixing this one out, and if somebody
else starts complaining about, then we can always add more guards (one
could be to check if the wrong usage min/max are 0-255). We could also
simply add "if vendor == MICROSOFT" or something in that spirit.

Right now I'd better try this just in case this wrong report descriptor
is used in different hardware.

Regarding the flag solution, if you are thinking at a kernel module
parameter,  I'd better not to. The reason being that once the word is
spread that you can "fix" your device by adding a simple module
parameter, people tend to forget to report bugs. I have seen countless
of forums/threads saying that you have to disable i2c-hid to have your
touchpad working, even when this is just not required.

Well, if Jiri is willing to add more checks and flags, we can always,
but I'd rather not.

Last, I'll request those patches to be included in Fedora when Jiri
takes them (or a future revision). We should have enough angry users
once it hits Fedora if there are some :)

Cheers,
Benjamin

> 
> Cheers,
>    Michek
> 
> > Link: https://bugzilla.redhat.com/show_bug.cgi?id=1325354
> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=28912
> > Link: https://github.com/ValveSoftware/steam-for-linux/issues/3384
> > Link: https://bugzilla.redhat.com/show_bug.cgi?id=1325354
> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=37982
> >
> > Signed-off-by: Benjamin Tissoires <benjamin.tissoires@...hat.com>
> > ---
> >  drivers/hid/hid-input.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git a/drivers/hid/hid-input.c b/drivers/hid/hid-input.c
> > index 14dd974..55db584 100644
> > --- a/drivers/hid/hid-input.c
> > +++ b/drivers/hid/hid-input.c
> > @@ -604,6 +604,15 @@ static void hidinput_configure_usage(struct
> hid_input *hidinput, struct hid_fiel
> >                         break;
> >                 }
> >
> > +               /*
> > +                * Some lazy vendors declare 255 usages for System
> Control,
> > +                * leading to the creation of ABS_X|Y axis and too many
> others.
> > +                * It wouldn't be a problem if joydev doesn't consider the
> > +                * device as a joystick then.
> > +                */
> > +               if (field->application == HID_GD_SYSTEM_CONTROL)
> > +                       goto ignore;
> > +
> >                 if ((usage->hid & 0xf0) == 0x90) {      /* D-pad */
> >                         switch (usage->hid) {
> >                         case HID_GD_UP:    usage->hat_dir = 1; break;
> > --
> > 2.7.4
> >
> > --
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