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Date:   Sat, 1 Oct 2022 22:58:00 +0200
From:   Sebastian Reichel <sebastian.reichel@collabora.com>
To:     ChiYuan Huang <u0084500@gmail.com>
Cc:     robh+dt@kernel.org, krzysztof.kozlowski+dt@linaro.org,
        mazziesaccount@gmail.com, alina_yu@richtek.com,
        cy_huang@richtek.com, alinayu829@gmail.com,
        linux-pm@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 3/3] Documentation: power: rt9471: Document exported
 sysfs entries
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Hi,

On Mon, Sep 19, 2022 at 09:11:09AM +0800, ChiYuan Huang wrote:
> Sebastian Reichel <sebastian.reichel@collabora.com> =E6=96=BC 2022=E5=B9=
=B49=E6=9C=8817=E6=97=A5 =E9=80=B1=E5=85=AD =E4=B8=8A=E5=8D=889:19=E5=AF=AB=
=E9=81=93=EF=BC=9A
> > On Thu, Sep 15, 2022 at 12:30:15AM +0800, cy_huang wrote:
> > > From: ChiYuan Huang <cy_huang@richtek.com>
> > >
> > > Document the settings exported by rt9471 charger driver through sysfs=
 entries:
> > > - sysoff_enable
> > > - port_detect_enable
> > >
> > > Signed-off-by: ChiYuan Huang <cy_huang@richtek.com>
> > > ---
> > > Since v5:
> > > - Recover all the change in sysfs-class-power.
> > > - New a sysfs-class-power-rt9471 file.
> > > - Remove 'charge_term_enable' sysfs entry, directly integrate it in
> > >   'charge_term_current' power supply property control.
> > >
> > > ---
> > >  Documentation/ABI/testing/sysfs-class-power-rt9471 | 29 ++++++++++++=
++++++++++
> > >  1 file changed, 29 insertions(+)
> > >  create mode 100644 Documentation/ABI/testing/sysfs-class-power-rt9471
> > >
> > > diff --git a/Documentation/ABI/testing/sysfs-class-power-rt9471 b/Doc=
umentation/ABI/testing/sysfs-class-power-rt9471
> > > new file mode 100644
> > > index 00000000..ad5b049
> > > --- /dev/null
> > > +++ b/Documentation/ABI/testing/sysfs-class-power-rt9471
> > > @@ -0,0 +1,29 @@
> > > +What:                /sys/class/power_supply/rt9471-*/sysoff_enable
> > > +Date:                Oct 2022
> > > +KernelVersion:       6.1
> > > +Contact:     ChiYuan Huang <cy_huang@richtek.com>
> > > +Description:
> > > +             This entry allows enabling the sysoff mode of rt9471 ch=
arger devices.
> > > +             If enabled and the input is removed, the internal batte=
ry FET is turned
> > > +             off to reduce the leakage from the BAT pin. See device =
datasheet for details.
> > > +             It's commonly used when the product enter shipping stag=
e.
> > > +
> > > +             Access: Read, Write
> > > +             Valid values:
> > > +             - 1: enabled
> > > +             - 0: disabled
> >
> > I still fail to see why this needs to be controllable at runtime.
> > This looks like a hardware property. Are there any known products,
> > which need this disabled?
> It's just a switch, actually 'disabled' is not needed.
> For the enabled case, mostly used in below scenarios
> 1. Online testing, USB IN -> Factory testing -> write 1 to enable ->
> USB out -> immediately VSYS off -> pack
> 2. Offline testing no vbus -> Factory testing -> write 1 to enable ->
> immediately VSYS off -> pack
>=20
> The 'disable" can use to cancel the shipping mode in case 1 before USB ou=
t.
> It's more like the testing.
>=20
> Like as you said, shipping BATFET_OFF is all the hardware behavior.
> To leave this mode after VSYS off, there're three ways
> 1. power key pressed
> 2. VBUS IN
> 3. control BATFET_OFF to 0 (But it need SOC to be alive, at the time,
> VSYS off, no one can execute this I2C command)

If factory testing and preperation is the only use case, I don't
think exposing this in sysfs and creating userspace ABI is worth
it. Just tell factory to use i2c-dev and poke the correct registers.

> If what you care is no need to mention 'disable', then just remove it.
> It's fine.
> >
> > > +What:                /sys/class/power_supply/rt9471-*/port_detect_en=
able
> > > +Date:                Oct 2022
> > > +KernelVersion:       6.1
> > > +Contact:     ChiYuan Huang <cy_huang@richtek.com>
> > > +Description:
> > > +             This entry allows enabling the USB BC12 port detect fun=
ction of rt9471 charger
> > > +             devices. If enabled and VBUS is inserted, device will s=
tart to do the BC12
> > > +             port detect and report the usb port type when port dete=
ct is done. See
> > > +             datasheet for details. Normally controlled when TypeC/U=
SBPD port integrated.
> > > +
> > > +             Access: Read, Write
> > > +             Valid values:
> > > +             - 1: enabled
> > > +             - 0: disabled
> >
> > So basically this depends on the hardware integration (e.g. it
> > should be disabled when power source is a DC barrel jack instead
> > of USB) and is not supposed to change at all during runtime? Then
> > the information wether it needs to be enabled should be derived
> > from the device tree.
>
> It's a switching charger integrates OTG boost.
> For the case 'DC Jack', there's no need to use this kind of product.
>=20
> With typec integration, at most time, it still need bc12 to be enabled
> by default. Just in some case, like as power role swap (SNK -> SRC -> SNK=
),
> to automatically identify the USB port, this may interrupt USB communicat=
ion.
>=20
> So as my understanding, keep it enabled by default, just in some case,
> it my need to control at runtime.

This should be part of the description. You can drop the sentence
"Normally controlled when TypeC/USBPD port integrated.", since
that's hard to comprehend. Instead add the information that this
is supposed to be always enabled, but can be disabled to avoid
USB link loss (?) when doing a USB PD role swap.

-- Sebastian

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