Date:   Tue, 31 May 2022 08:31:37 -0700
From:   Roderick Colenbrander <thunderbird2k@...il.com>
To:     Martino Fontana <tinozzo123@...il.com>
Cc:     Max Fletcher <fletcher0max@...il.com>,
        "Daniel J. Ogorchock" <djogorchock@...il.com>,
        Jiri Kosina <jikos@...nel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        linux-input <linux-input@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] HID: nintendo: fix face button mappings

On Tue, May 31, 2022 at 8:19 AM Martino Fontana <tinozzo123@...il.com> wrote:
>
>  > Second, even if the patch was right it would be tricky to merge. The
>  > problem is that a changed mapping breaks user spaces and in general
>  > can't do this unless there is a really good reason. It just would
>  > break existing applications and libraries (often e.g. SDL)
>
> The problem is that the userspace is already broken.
> If, out of the box, you attempt to launch something that uses SDL (like
> Wine, or Super Tux Kart), the mapping you'll get will be wrong (and not
> visually, the buttons are literally swapped).
> Right now, this can be worked around (it makes the mapping correct) by
> setting an environment variable (which isn't a thing that a user is
> supposed to be doing, and the patch will remove the need of it):
> ```
> SDL_GAMECONTROLLERCONFIG=050000007e0500000920000001800000,Nintendo
> Switch Pro
> Controller,platform:Linux,a:b0,b:b1,x:b3,y:b2,back:b9,guide:b11,start:b10,leftstick:b12,rightstick:b13,leftshoulder:b5,rightshoulder:b6,dpup:h0.1,dpdown:h0.4,dpleft:h0.8,dpright:h0.2,leftx:a0,lefty:a1,rightx:a2,righty:a3,lefttrigger:b7,righttrigger:b8,030000007e0500000920000011810000,Nintendo
> Switch Pro
> Controller,platform:Linux,a:b0,b:b1,x:b3,y:b2,back:b9,guide:b11,start:b10,leftstick:b12,rightstick:b13,leftshoulder:b5,rightshoulder:b6,dpup:h0.1,dpdown:h0.4,dpleft:h0.8,dpright:h0.2,leftx:a0,lefty:a1,rightx:a2,righty:a3,lefttrigger:b7,righttrigger:b8,060000007e0500000620000000000000,Nintendo
> Switch Combined
> Joy-Cons,platform:Linux,a:b0,b:b1,x:b3,y:b2,back:b9,guide:b11,start:b10,leftstick:b12,rightstick:b13,leftshoulder:b5,rightshoulder:b6,dpup:b14,dpdown:b15,dpleft:b16,dpright:b17,leftx:a0,lefty:a1,rightx:a2,righty:a3,lefttrigger:b7,righttrigger:b8,
> ```
> The weird thing however is that SDL should already uses a controller
> database:
> https://github.com/libsdl-org/SDL/blob/main/src/joystick/SDL_gamecontrollerdb.h.
> If this problem is caused by an SDL bug (I don't know if it is), then
> it's SDL that will need a patch, and the problem will be solved with
> zero repercussions. I think that SDL should be investigated before
> continuing to discuss this.

It looks like SDL lacks the patch to deal with the upstream driver
properly. The chicken and egg problem SDL there is between the kernel
and SDL, is that SDL supports a device prior to there being a kernel
driver (or there being enough penetration for one). Without a driver,
many devices function with an often strange mapping. That's the
mapping SDL has in its table (for hid-generic). When a kernel driver
comes around with a different, but proper mapping there is an issue.

At the time we first dealt with this for DualShock 3 / 4 devices. The
trick used then was to patch the 'version' bit of the HID device with
'0x8000'. This resulted in a different mapping line. To understand SDL
uses a GUID as the index for the table, it is composed of
vendor/product id, version id and other fiels. The patched version,
resulted in a different GUID, which then allowed SDL2 to recognize the
device properly as it would use a different mapping line.

For the Switch controllers, it looks like no patched line was added.
Someone would need to provide a patch.

> If, however, SDL is working as intended (making the patch necessary) and
> this patch is merged, it will make the mapping correct out of the box
> but it will also break a few things:
> - Those who were using this workaround will have to remove it (by the
> way, the page on the Arch Wiki should be updated too:
> https://wiki.archlinux.org/title/Gamepad#Using_hid-nintendo_with_SDL2_Games);
> - Applications that use raw joydev/evdev mappings (like Dolphin
> Emulator) will have to be reconfigured.
> - Also, some applications use SDL2 mappings in a different way (for
> example, PCSX2), so out of the box the mappings are applied and the
> controller is mapped as expected. Merging the patch will break
> applications like these (in PCSX2's case it will be temporary since its
> database is updated weekly, but it will force the user to use the new
> kernel version, otherwise they will be stuck with a wrong mapping).
>
> Whether it's a wise idea to merge this as soon as possible in order to
> cause the least amount amount of breakage, is not my call.
>
>
> On 13/05/22 21:58, Roderick Colenbrander wrote:
> > Hi Max,
> >
> > Thanks for your patch, however I must say the patch is not correct for
> > 2 reasons.
> >
> > Over the years different controllers have different layouts. The
> > standard which this driver (as well as others such as
> > hid-sony/hid-playstation) follow is the Linux gamepad standard (see
> > Documentation/input/gamepad.rst). It stays away of the debate what is
> > A/B/X/Y. It talks about North/west/.., (yes they are macros which map
> > to A/B/X/Y). In case of the Switch it does mean things are flipped,
> > but it was not meant to represent an Xbox controller. (Technically one
> > could argue that the Xbox controller should be flipped as it was the
> > SNES controller back in the days which introduced X/Y and the Switch
> > is still consistent with that.)
> >
> > Second, even if the patch was right it would be tricky to merge. The
> > problem is that a changed mapping breaks user spaces and in general
> > can't do this unless there is a really good reason. It just would
> > break existing applications and libraries (often e.g. SDL)
> >
> > Thanks,
> > Roderick
> >
> > On Wed, May 11, 2022 at 8:12 PM Max Fletcher <fletcher0max@...il.com> wrote:
> >>
> >> Previously, A and B would match the Xbox layout, but X and Y were incorrectly swapped. This corrects it so that X and Y match the Xbox layout.
> >>
> >> Signed-off-by: Max Fletcher <fletcher0max@...il.com>
> >> ---
> >>   drivers/hid/hid-nintendo.c | 10 +++++-----
> >>   1 file changed, 5 insertions(+), 5 deletions(-)
> >>
> >> diff --git a/drivers/hid/hid-nintendo.c b/drivers/hid/hid-nintendo.c
> >> index 2204de889739..7735971ede3f 100644
> >> --- a/drivers/hid/hid-nintendo.c
> >> +++ b/drivers/hid/hid-nintendo.c
> >> @@ -1351,10 +1351,10 @@ static void joycon_parse_report(struct joycon_ctlr *ctlr,
> >>                  input_report_key(dev, BTN_START, btns & JC_BTN_PLUS);
> >>                  input_report_key(dev, BTN_THUMBR, btns & JC_BTN_RSTICK);
> >>                  input_report_key(dev, BTN_MODE, btns & JC_BTN_HOME);
> >> -               input_report_key(dev, BTN_WEST, btns & JC_BTN_Y);
> >> -               input_report_key(dev, BTN_NORTH, btns & JC_BTN_X);
> >> -               input_report_key(dev, BTN_EAST, btns & JC_BTN_A);
> >> -               input_report_key(dev, BTN_SOUTH, btns & JC_BTN_B);
> >> +               input_report_key(dev, BTN_X, btns & JC_BTN_Y);
> >> +               input_report_key(dev, BTN_Y, btns & JC_BTN_X);
> >> +               input_report_key(dev, BTN_B, btns & JC_BTN_A);
> >> +               input_report_key(dev, BTN_A, btns & JC_BTN_B);
> >>          }
> >>
> >>          input_sync(dev);
> >> @@ -1578,7 +1578,7 @@ static const unsigned int joycon_button_inputs_l[] = {
> >>
> >>   static const unsigned int joycon_button_inputs_r[] = {
> >>          BTN_START, BTN_MODE, BTN_THUMBR,
> >> -       BTN_SOUTH, BTN_EAST, BTN_NORTH, BTN_WEST,
> >> +       BTN_A, BTN_B, BTN_Y, BTN_X,
> >>          BTN_TR, BTN_TR2,
> >>          0 /* 0 signals end of array */
> >>   };
> >> --
> >> 2.35.3
> >>
> >
> >

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