Date:   Mon, 12 Aug 2019 18:57:37 +0200
From:   Benjamin Tissoires <benjamin.tissoires@...il.com>
To:     João Moreno <mail@...omoreno.com>
Cc:     Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        Jiri Kosina <jikos@...nel.org>,
        "open list:HID CORE LAYER" <linux-input@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] HID: apple: Fix stuck function keys when using FN

Hi João,

On Thu, Aug 8, 2019 at 10:35 PM João Moreno <mail@...omoreno.com> wrote:
>
> Hi Benjamin,
>
> On Mon, 8 Jul 2019 at 22:35, João Moreno <mail@...omoreno.com> wrote:
> >
> > Hi Benjamin,
> >
> > No worries, also pretty busy over here. Didn't mean to press.
> >
> > On Mon, 1 Jul 2019 at 10:32, Benjamin Tissoires
> > <benjamin.tissoires@...hat.com> wrote:
> > >
> > > Hi João,
> > >
> > > On Sun, Jun 30, 2019 at 10:15 PM João Moreno <mail@...omoreno.com> wrote:
> > > >
> > > > Hi Jiri & Benjamin,
> > > >
> > > > Let me know if you need something else to get this patch moving forward. This
> > > > fixes an issue I hit daily, it would be great to get it fixed.
> > >
> > > Sorry for the delay, I am very busy with internal corporate stuff, and
> > > I tried setting up a new CI system at home, and instead of spending a
> > > couple of ours, I am down to 2 weeks of hard work, without possibility
> > > to switch to the new right now :(
> > > Anyway.
> > >
> > > >
> > > > Thanks.
> > > >
> > > > On Mon, 10 Jun 2019 at 23:31, Joao Moreno <mail@...omoreno.com> wrote:
> > > > >
> > > > > This fixes an issue in which key down events for function keys would be
> > > > > repeatedly emitted even after the user has raised the physical key. For
> > > > > example, the driver fails to emit the F5 key up event when going through
> > > > > the following steps:
> > > > > - fnmode=1: hold FN, hold F5, release FN, release F5
> > > > > - fnmode=2: hold F5, hold FN, release F5, release FN
> > >
> > > Ouch :/
> > >
> >
> > Right?!
> >
> > > > >
> > > > > The repeated F5 key down events can be easily verified using xev.
> > > > >
> > > > > Signed-off-by: Joao Moreno <mail@...omoreno.com>
> > > > > ---
> > > > >  drivers/hid/hid-apple.c | 21 +++++++++++----------
> > > > >  1 file changed, 11 insertions(+), 10 deletions(-)
> > > > >
> > > > > diff --git a/drivers/hid/hid-apple.c b/drivers/hid/hid-apple.c
> > > > > index 1cb41992aaa1..81867a6fa047 100644
> > > > > --- a/drivers/hid/hid-apple.c
> > > > > +++ b/drivers/hid/hid-apple.c
> > > > > @@ -205,20 +205,21 @@ static int hidinput_apple_event(struct hid_device *hid, struct input_dev *input,
> > > > >                 trans = apple_find_translation (table, usage->code);
> > > > >
> > > > >                 if (trans) {
> > > > > -                       if (test_bit(usage->code, asc->pressed_fn))
> > > > > -                               do_translate = 1;
> > > > > -                       else if (trans->flags & APPLE_FLAG_FKEY)
> > > > > -                               do_translate = (fnmode == 2 && asc->fn_on) ||
> > > > > -                                       (fnmode == 1 && !asc->fn_on);
> > > > > +                       int fn_on = value ? asc->fn_on :
> > > > > +                               test_bit(usage->code, asc->pressed_fn);
> > > > > +
> > > > > +                       if (!value)
> > > > > +                               clear_bit(usage->code, asc->pressed_fn);
> > > > > +                       else if (asc->fn_on)
> > > > > +                               set_bit(usage->code, asc->pressed_fn);
> > >
> > > I have the feeling that this is not the correct fix here.
> > >
> > > I might be wrong, but the following sequence might also mess up the
> > > driver state, depending on how the reports are emitted:
> > > - hold FN, hold F4, hold F5, release F4, release FN, release F5
> > >
> >
> > I believe this should be fine. Following the code:
> >
> > - hold FN, sets asc->fn_on to true
> > - hold F4, in the trans block fn_on will be true and we'll set the F4
> > bit in the bitmap
> > - hold F5, in the trans block fn_on will be true and we'll set the F5 bit
> > - release F4, in the trans block fn_on will be true (because of the bitmap) and
> > we'll clear the F4 bit
> > - release FN, asc->fn_on will be false, but it doesn't matter since...
> > - release F5, in the trans block we'll look into the bitmap (instead
> > of asc->fn_on),
> > so fn_on will be true and we'll clear the F5 bit
> >
> > I tested it in practice using my changes:
> >
> > Interestingly the Apple keyboard doesn't seem to emit an even for F5 when F4 is
> > pressed, seems like a hardware limitation. But F6 does work. So, when I execute
> > these events in that order, everything works as it should: xev reports
> > the following:
> >
> > KeyPress F4
> > KeyPress F6
> > KeyRelease F4
> > KeyRelease F6
> >
> > > The reason is that the driver only considers you have one key pressed
> > > with the modifier, and as the code changed its state based on the last
> > > value.
> > >
> >
> > I believe the bitmap takes care of storing the FN state per key press. The
> > trick I did was to check on the global `asc->fn_on` state only when a key
> > is pressed, but check on the bitmap instead when it's released.
> >
> > Let me know what you think. Am I missing something here?
> >
> > Cheers,
> > João.
> >
> > > IMO a better fix would:
> > >
> > > - keep the existing `trans` mapping lookout
> > > - whenever a `trans` mapping gets found:
> > >   * get both translated and non-translated currently reported values
> > > (`test_bit(keycode, input_dev->key)`)
> > >   * if one of them is set to true, then consider the keycode to be the
> > > one of the key (no matter fn_on)
> > >     -> deal with `value` with the corrected keycode
> > >   * if the key was not pressed:
> > >     -> chose the keycode based on `fn_on` and `fnmode` states
> > >     and report the key press event
> > >
> > > This should remove the nasty pressed_fn state which depends on the
> > > other pressed keys.
> > >
> > > Cheers,
> > > Benjamin
> > >
> > > > > +
> > > > > +                       if (trans->flags & APPLE_FLAG_FKEY)
> > > > > +                               do_translate = (fnmode == 2 && fn_on) ||
> > > > > +                                       (fnmode == 1 && !fn_on);
> > > > >                         else
> > > > >                                 do_translate = asc->fn_on;
> > > > >
> > > > >                         if (do_translate) {
> > > > > -                               if (value)
> > > > > -                                       set_bit(usage->code, asc->pressed_fn);
> > > > > -                               else
> > > > > -                                       clear_bit(usage->code, asc->pressed_fn);
> > > > > -
> > > > >                                 input_event(input, usage->type, trans->to,
> > > > >                                                 value);
> > > > >
> > > > > --
> > > > > 2.19.1
> > > > >
>
> Gave this another look and I still haven't found any issues, let me
> know if you still
> think I'm missing something. Thanks!
>

OK, I am tempted to take the patch, but I'll need to add this as a
regression test in my test-suite. This is too complex that it can
easily break next time someone looks at it.

Can you send me the report descriptors of the device using
hid-recorder from hid-tools[0].
Ideally, if you can put the faulty sequence in the logs, that would
help writing down the use case.

Cheers,
Benjamin

[0] https://gitlab.freedesktop.org/libevdev/hid-tools

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