linux-kernel - Re: [PATCH v11 1/4] HID: wacom_sys: Add support for flipping the data values

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Date:   Wed, 20 Oct 2021 13:46:08 +0200
From:   Benjamin Tissoires <benjamin.tissoires@...hat.com>
To:     Alistair Francis <alistair23@...il.com>
Cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Ping Cheng <pinglinux@...il.com>,
        Alistair Francis <alistair@...stair23.me>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        dl-linux-imx <linux-imx@....com>, Jiri Kosina <jikos@...nel.org>,
        linux-input <linux-input@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v11 1/4] HID: wacom_sys: Add support for flipping the data values

On Wed, Oct 20, 2021 at 1:28 PM Alistair Francis <alistair23@...il.com> wrote:
>
> On Wed, Oct 20, 2021 at 12:14 PM Dmitry Torokhov
> <dmitry.torokhov@...il.com> wrote:
> >
> > On Wed, Oct 20, 2021 at 11:44:50AM +1000, Alistair Francis wrote:
> > > On Wed, Oct 20, 2021 at 11:05 AM Dmitry Torokhov
> > > <dmitry.torokhov@...il.com> wrote:
> > > >
> > > > On Wed, Oct 20, 2021 at 09:33:13AM +1000, Alistair Francis wrote:
> > > > > On Tue, Oct 19, 2021 at 11:51 AM Dmitry Torokhov
> > > > > <dmitry.torokhov@...il.com> wrote:
> > > > > >
> > > > > > We already have touchscreen-inverted-x/y defined in
> > > > > > Documentation/devicetree/bindings/input/touchscreen/touchscreen.yaml,
> > > > > > why are they not sufficient?
> > > > >
> > > > > The touchscreen-* properties aren't applied to HID devices though, at
> > > > > least not that I can tell.
> > > >
> > > > No, they are not currently, but that does not mean we need to establish
> > > > a new set of properties (property names) for HID case.
> > >
> > > I can update the names to use the existing touchscreen ones.
> > >
> > > Do you have a hint of where this should be implemented though?
> > >
> > > Right now (without "HID: wacom: Add support for the AG14 Wacom
> > > device") the wacom touchscreen is just registered as a generic HID
> > > device. I don't see any good place in hid-core, hid-input or
> > > hid-generic to invert the input values for this.
> >
> > I think the transformation should happen in
> > hid-multitouch.c::mt_process_slot() using helpers from
> > include/linux/input/touchscreen.h
>
> Thanks for the help!
>
> I have managed to get the device to be a hid-multitouch (instead of
> hid-generic).
>
> I also think I have figured out a way to get the properties to
> hid-multitouch from the i2c-hid device. It requires a change to
> touchscreen.c, but it's not a big change.
>
> The main problem now is that hid-multitouch.c::mt_process_slot() isn't
> actually called. The code just calls input_sync() from
> hid-multitouch.c::mt_report(). It doesn't get to mt_process_slot() due
> to rdata->is_mt_collection not being true. Setting
> rdata->is_mt_collection to true causes userspace not to see the wacom
> input any more.

hid-multitouch now only handles the mutltitouch part. Everything else
is handled in hid-input.c
So if the device is just presenting a stylus to the user space, you
better not use hid-multitouch at all, but hid-generic.

Cheers,
Benjamin

>
> Alistair
>
> >
> > I think the more challenging question is to how pass/attach struct
> > touchscreen_properties * to the hid device (i expect the properties will
> > be attached to i2c-hid device, but maybe we could create a sub-node of
> > it and attach properties there.
> >
> > Thanks.
> >
> > --
> > Dmitry
>