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Date:   Tue, 20 Sep 2022 16:53:45 +0000
To:     Benjamin Tissoires <benjamin.tissoires@redhat.com>
From:   Johnothan King <johnothanking@protonmail.com>
Cc:     "Daniel J. Ogorchock" <djogorchock@gmail.com>,
        Jiri Kosina <jikos@kernel.org>,
        "linux-input@vger.kernel.org" <linux-input@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] HID: nintendo: check analog user calibration for plausibility
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> Wouldn't it make sense to have a function that takes a single struct
> joycon_stick_cal pointer and does the check?

I acknowledge the current code can be simplified further. I will submit a s=
econd version of this patch that moves the plausibility check to joycon_rea=
d_stick_calibration() and adds a joycon_use_default_calibration() function.=
 This will avoid the code duplication present in the current patch.

In the v2 patch the check will still use both the cal_x and cal_y pointers.=
 However, since the check will be reduced to just one if statement, that sh=
ould be enough to simplify the code. The new function in the v2 patch (joyc=
on_use_default_calibration()) was implemented so that I could simplify the =
existing default stick calibration code for reuse with both the left and ri=
ght sticks. The new function in effect reduces four lines of code to one:
    -ctlr->left_stick_cal_x.center =3D DFLT_STICK_CAL_CEN;
    -ctlr->left_stick_cal_y.center =3D DFLT_STICK_CAL_CEN;
    -ctlr->right_stick_cal_x.center =3D DFLT_STICK_CAL_CEN;
    -ctlr->right_stick_cal_y.center =3D DFLT_STICK_CAL_CEN;
    +cal_x->center =3D cal_y->center =3D DFLT_STICK_CAL_CEN;

- Johnothan King

------- Original Message -------
On Tuesday, September 20th, 2022 at 3:21 AM, Benjamin Tissoires <benjamin.t=
issoires@redhat.com> wrote:


> On Wed, Sep 14, 2022 at 9:51 AM Johnothan King
> johnothanking@protonmail.com wrote:
>=20
> > Arne Wendt writes:
> > Cheap clone controllers may (falsely) report as having a user
> > calibration for the analog sticks in place, but return
> > wrong/impossible values for the actual calibration data.
> > In the present case at mine, the controller reports having a
> > user calibration in place and successfully executes the read
> > commands. The reported user calibration however is
> > min =3D center =3D max =3D 0.
> >=20
> > This pull request addresses problems of this kind by checking the
> > provided user calibration-data for plausibility (min < center < max)
> > and falling back to the default values if implausible.
> >=20
> > I'll note that I was experiencing a crash because of this bug when usin=
g
> > the GuliKit KingKong 2 controller. The crash manifests as a divide by
> > zero error in the kernel logs:
> > kernel: divide error: 0000 [#1] PREEMPT SMP NOPTI
> >=20
> > Link: https://github.com/nicman23/dkms-hid-nintendo/pull/25
> > Link: https://github.com/DanielOgorchock/linux/issues/36
> > Co-authored-by: Arne Wendt arne.wendt@tuhh.de
> > Signed-off-by: Johnothan King johnothanking@protonmail.com
> > ---
> > drivers/hid/hid-nintendo.c | 24 ++++++++++++++++++++++--
> > 1 file changed, 22 insertions(+), 2 deletions(-)
> >=20
> > diff --git a/drivers/hid/hid-nintendo.c b/drivers/hid/hid-nintendo.c
> > index 6028af3c3aae..7f287f6a75f5 100644
> > --- a/drivers/hid/hid-nintendo.c
> > +++ b/drivers/hid/hid-nintendo.c
> > @@ -793,7 +793,17 @@ static int joycon_request_calibration(struct joyco=
n_ctlr ctlr)
> > &ctlr->left_stick_cal_x,
> > &ctlr->left_stick_cal_y,
> > true);
> > - if (ret) {
> > +
> > + /
> > + * Check whether read succeeded and perform plausibility check
> > + * for retrieved values.
> > + */
> > + if (ret ||
> > + ctlr->left_stick_cal_x.min >=3D ctlr->left_stick_cal_x.center ||
> > + ctlr->left_stick_cal_x.center >=3D ctlr->left_stick_cal_x.max ||
> > + ctlr->left_stick_cal_y.min >=3D ctlr->left_stick_cal_y.center ||
> > + ctlr->left_stick_cal_y.center >=3D ctlr->left_stick_cal_y.max
> > + ) {
> > hid_warn(ctlr->hdev,
> > "Failed to read left stick cal, using dflts; e=3D%d\n",
> > ret);
> > @@ -812,7 +822,17 @@ static int joycon_request_calibration(struct joyco=
n_ctlr ctlr)
> > &ctlr->right_stick_cal_x,
> > &ctlr->right_stick_cal_y,
> > false);
> > - if (ret) {
> > +
> > + /
> > + * Check whether read succeeded and perform plausibility check
> > + * for retrieved values.
> > + */
> > + if (ret ||
> > + ctlr->right_stick_cal_x.min >=3D ctlr->right_stick_cal_x.center ||
> > + ctlr->right_stick_cal_x.center >=3D ctlr->right_stick_cal_x.max ||
> > + ctlr->right_stick_cal_y.min >=3D ctlr->right_stick_cal_y.center ||
> > + ctlr->right_stick_cal_y.center >=3D ctlr->right_stick_cal_y.max
>=20
>=20
> Wouldn't it make sense to have a function that takes a single struct
> joycon_stick_cal pointer and does the check?
> This would make things more readable IMO.
>=20
> Cheers,
> Benjamin
>=20
> > + ) {
> > hid_warn(ctlr->hdev,
> > "Failed to read right stick cal, using dflts; e=3D%d\n",
> > ret);
> > --
> > 2.37.3