linux-kernel - Re: [PATCH 4/5] usb: typec: ucsi: make it orientation-aware

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Message-ID: <CAA8EJppzVuFX0FE914teBmnH8NFnASYvPku+wqkMuWQH5YEi5Q@mail.gmail.com>
Date: Tue, 9 Apr 2024 13:21:05 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Neil Armstrong <neil.armstrong@...aro.org>, 
	linux-usb@...r.kernel.org, linux-arm-msm@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] usb: typec: ucsi: make it orientation-aware

On Tue, 9 Apr 2024 at 11:05, Heikki Krogerus
<heikki.krogerus@...ux.intel.com> wrote:
>
> Hi Dmitry,
>
> On Mon, Apr 08, 2024 at 07:30:52AM +0300, Dmitry Baryshkov wrote:
> > The UCSI 1.0 is not orientation aware. Only UCSI 2.0 has added
> > orientation status to GET_CONNECTOR_STATUS data. However the glue code
> > can be able to detect cable orientation on its own (and report it via
> > corresponding typec API). Add a flag to let UCSI mark registered ports
> > as orientation aware.
> >
> > Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> > ---
> >  drivers/usb/typec/ucsi/ucsi.c | 2 ++
> >  drivers/usb/typec/ucsi/ucsi.h | 1 +
> >  2 files changed, 3 insertions(+)
> >
> > diff --git a/drivers/usb/typec/ucsi/ucsi.c b/drivers/usb/typec/ucsi/ucsi.c
> > index 7ad544c968e4..6f5adc335980 100644
> > --- a/drivers/usb/typec/ucsi/ucsi.c
> > +++ b/drivers/usb/typec/ucsi/ucsi.c
> > @@ -1551,6 +1551,8 @@ static int ucsi_register_port(struct ucsi *ucsi, struct ucsi_connector *con)
> >       cap->svdm_version = SVDM_VER_2_0;
> >       cap->prefer_role = TYPEC_NO_PREFERRED_ROLE;
> >
> > +     cap->orientation_aware = !!(ucsi->quirks & UCSI_ORIENTATION_AWARE);
> > +
> >       if (con->cap.op_mode & UCSI_CONCAP_OPMODE_AUDIO_ACCESSORY)
> >               *accessory++ = TYPEC_ACCESSORY_AUDIO;
> >       if (con->cap.op_mode & UCSI_CONCAP_OPMODE_DEBUG_ACCESSORY)
> > diff --git a/drivers/usb/typec/ucsi/ucsi.h b/drivers/usb/typec/ucsi/ucsi.h
> > index 6599fbd09bee..e92be45e4c1c 100644
> > --- a/drivers/usb/typec/ucsi/ucsi.h
> > +++ b/drivers/usb/typec/ucsi/ucsi.h
> > @@ -410,6 +410,7 @@ struct ucsi {
> >       unsigned long quirks;
> >  #define UCSI_NO_PARTNER_PDOS BIT(0)  /* Don't read partner's PDOs */
> >  #define UCSI_DELAY_DEVICE_PDOS       BIT(1)  /* Reading PDOs fails until the parter is in PD mode */
> > +#define UCSI_ORIENTATION_AWARE       BIT(2)  /* UCSI is orientation aware */
>
> You are not using that flag anywhere in this series. But why would
> orientation need a "quirk" in the first place?

Patch 5 sets this flag.

> I'm not sure where you are going with this, but please try to avoid
> the quirk flags in general in this driver rather than considering them
> as the first way of solving things. Use them only as the last resort.
>
> I don't want this driver to end up like xhci and some other drivers,
> where refactoring is almost impossible because every place is full of
> conditions checking the quirks, and where in worst case a quirk meant
> to solve a problem on one hardware causes problems on another.

Enabling the orientation_aware flag in the capabilities enables the
`class/typec/portN/orientation` attribute to be visible. This way
userspace (and more importantly the developer) can detect in which way
the cable is plugged. We have had several issues with the driver
mis-detecting the orientation and having the valid orientation
attribute helped us a lot.

Note, the UCSI 1.x doesn't report orientation at all. So by default
the UCSI driver isn't orientation aware, it doesn't call
typec_set_orientation(), etc. UCSI 2.0 introduced the orientation flag
in the GET_CONNECTOR_STATUS data, but currently the driver just
ignores it. If we enable orientation_aware by default this will result
in the useless 'unknown' value for that attribute. I think this is
what Badhri tried to evade when he introduced the orientation_aware
flag.

We can probably get the same result by adding the port_capabilities()
callback to be called just before ucsi_register_port_psy() and
typec_register_port(). Would it be better from your point of view?

--
With best wishes
Dmitry