Re: [PATCHv3 1/2] dt-bindings: usb: typec: anx7688: start a binding document

[Ondřej Jirman]

Hi Krzysztof,

On Mon, Apr 08, 2024 at 01:17:32PM GMT, Krzysztof Kozlowski wrote:
> On 08/04/2024 12:51, Pavel Machek wrote:
> > Add binding for anx7688 usb type-c bridge. I don't have a datasheet,
> > but I did best I could.
> > 
> > Signed-off-by: Pavel Machek <pavel@xxxxxx>
> 
> ...
> 
> > +  cabledet-gpios:
> > +    maxItems: 1
> > +    description: GPIO controlling CABLE_DET (C3) pin.
> > +
> > +  avdd10-supply:
> > +    description: 1.0V power supply going to AVDD10 (A4, ...) pins
> > +
> > +  dvdd10-supply:
> > +    description: 1.0V power supply going to DVDD10 (D6, ...) pins
> > +
> > +  avdd18-supply:
> > +    description: 1.8V power supply going to AVDD18 (E3, ...) pins
> > +
> > +  dvdd18-supply:
> > +    description: 1.8V power supply going to DVDD18 (G4, ...) pins
> > +
> > +  avdd33-supply:
> > +    description: 3.3V power supply going to AVDD33 (C4, ...) pins
> > +
> > +  i2c-supply: true
> > +  vconn-supply: true
> 
> There are no such supplies like i2c and vconn on the schematics.

Which schematics?

ANX7688 has VCONN1/2_EN GPIOs that control a switching of VCONN power supply
to resective CCx pins. That's just a switch signal. Power for VCONN needs
to come from somewhere and the driver needs to enable the regulator at
the appropriate time only.

On Pinephone it can't be an always on power supply and needs to be enabled
only when used due to HW design of the circuit. (default without ANX driver
initialized would be to shove 5V to both CC pins, which breaks Type-C spec)

I2C supply is needed for I2C bus to work, apparently. There's nothing
that says that I2C pull-ups supply has to come from supplies powering the
chip. I2C I/O is open drain and the device needs to enable a bus supply
in order to communicate.

You can say that bus master should be managing the bus supply, but you'd still
have a problem that each device may be behind a voltage translator, and
logically, bus master driver should care only about its side of the bus then.
Both side of level shifter need the pull-up power enabled.

You can also make an argument that bus supply can be always on, but that
causes several other issues on Pinephone due to shared nature of most
resources like these. There are other devices on shared power rails, that
need to be turned off during sleep, etc.

Kind regards,
	o.

> I think this represents some other part of component which was added
> here only for convenience.
> 
> 
> 
> Best regards,
> Krzysztof
>