linux-kernel - Re: [PATCH v2 0/4] Stylus-on-touchscreen device support

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Message-ID: <20210503130015.d2qnahrrfyv3odqj@tarta.nabijaczleweli.xyz>
Date:   Mon, 3 May 2021 15:00:15 +0200
From:   наб <nabijaczleweli@...ijaczleweli.xyz>
To:     Benjamin Tissoires <benjamin.tissoires@...hat.com>
Cc:     Jiri Kosina <jikos@...nel.org>,
        Peter Hutterer <peter.hutterer@...-t.net>,
        "open list:HID CORE LAYER" <linux-input@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 0/4] Stylus-on-touchscreen device support

On Mon, May 03, 2021 at 11:52:43AM +0200, Benjamin Tissoires wrote:
> On Mon, May 3, 2021 at 11:39 AM Benjamin Tissoires
> <benjamin.tissoires@...hat.com> wrote:
> >
> > On Mon, May 3, 2021 at 11:11 AM Jiri Kosina <jikos@...nel.org> wrote:
> > >
> > > On Tue, 20 Apr 2021, наб wrote:
> > >
> > > > > This patchset adds support for stylus-on-touchscreen devices as found on
> > > > > the OneMix 3 Pro and Dell Inspiron 15 7000 2-in-1 (7591), among others;
> > > > > with it, they properly behave like a drawing tablet.
> > > > >
> > > > > Patches 2 and 4 funxionally depend on patch 1.
> > > > > Patch 4 needs patch 3 to apply.
> > > > >
> > > > > The output of this patchset and the need for a kernel, rather than
> > > > > userspace, patch was previously discussed here:
> > > > >   https://gitlab.freedesktop.org/libinput/libinput/-/merge_requests/558#note_792834
> > > > >
> > > > > Changes in v2:
> > > > > Patch 4 now ANDs the secondary button with the tip switch,
> > > > > since it's otherwise borderline useless to the user.
> > > > >
> > > > > Ahelenia Ziemiańska (4):
> > > > >   HID: multitouch: require Finger field to mark Win8 reports as MT
> > > > >   HID: multitouch: set Stylus suffix for Stylus-application devices, too
> > > > >   HID: input: replace outdated HID numbers+comments with macros
> > > > >   HID: input: work around Win8 stylus-on-touchscreen reporting
> > > > >
> > > > >  drivers/hid/hid-input.c      | 54 ++++++++++++++++++++++++++++++++++--
> > > > >  drivers/hid/hid-multitouch.c | 18 +++++++-----
> > > > >  2 files changed, 62 insertions(+), 10 deletions(-)
> > > > >
> > > > > --
> > > > > 2.20.1
> > > >
> > > > Bumping this after a monthish ‒ is it missing something? Am I?
> > >
> > > Benjamin had concerns about regressions and wanted to run a full battery
> > > of testing on it.
> > >
> > > Benjamin, is there any outcome of that, please?
> > >
> >
> > Sorry, no real outcome here.
> >
> > I ran the test suite, and there were no errors, until I realized that
> > there are no tests regarding tablets, so it can't detect any
> > regressions here.
> > And then, the usual happens, no time to actually work on the test suite... :(
> >
> > I'll do a "normal" review soon (i.e. today)
> >
> 
> So I did a quick pass at the patches:
> - 1/4 -> I think this one is safe and could go as it is, maybe with
> CC: stable on it. Any regressions should have been caught by the
> testsuite, so that's a good one.
> - 2/4 and 3/4 -> Ack on those 2 too, note stable material, but not
> necessary v5.13 material
> - 4/4 -> I honestly have no idea if the patch is correct or not. I
> would hold on this one until we have proper tests for those.
> 
> Jiri, would you be ok to split the series as this?

Splitting 2/4 away from 1/4 presents a minor cosmetic problem:
since 1/4 no longer tags the stylus-on-touchscreen device as MT,
the device name turns from "GXTP7386:00 27C6:0113 Stylus"
to "GXTP7386:00 27C6:0113", so the user is left with
two identically-named devices, the first of which corresponds
to the touchscreen, and the second to the stylus.

Granted, it might also append "Stylus" to names that could contain it,
but I haven't managed to trace where hdev->name is born to determine if
that's a concern.

> наб, would you be OK to work on the test suite at
> https://gitlab.freedesktop.org/libevdev/hid-tools so we can move
> forward for your last patch?
>
> The problem I see on the last patch is that it is touching a generic
> path and is not trivial. So adding tests would have 3 benefits:
> - we ensure we are doing the correct thing
> - we ensure we are not breaking existing devices (to some extent,
> given that the tests are non written for the tablets)
> - we ensure we are not breaking that in the future.

I'd be more than happy to add tests of some sort, but reading the
repository and tests/ under it has me positively stumped,
not a clue where an entry-point would be, or how I'd instrument a
reasonable test around my rdesc, so some sort of vague guidance
to that end would be greatly appreciated.

Best,
наб

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