Re: [PATCH 01/12] arm64: dts: allwinner: h6: Add Orange Pi 3 DTS

[Maxime Ripard <maxime.ripard@bootlin.com>]

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On Tue, Apr 09, 2019 at 12:58:51AM +0200, Ondřej Jirman wrote:
> > > +&usb2otg {
> > > +	dr_mode = "host";
> > > +	status = "okay";
> > > +};
> > > +
> > > +&usb2phy {
> > > +	usb0_id_det-gpios = <&pio 2 15 GPIO_ACTIVE_HIGH>; /* PC15 */
> > > +	usb0_vbus-supply = <&reg_vcc5v>;
> > > +	usb3_vbus-supply = <&reg_vcc5v>;
> > > +	status = "okay";
> >
> > If we have an ID pin, then why is the OTG controller set to host?
>
> This board has fixed conenction between VBUS and DCIN, so if it is powered
> from DCIN and someone will try to connect it to the PC as a peripheral,
> they'll get PC's VBUS shorted to the power supply connected to DCIN.
>
> Depending on voltage difference between DCIN and PC's VBUS, you can get
> overcurrent condidion and PC's port shutdown.
>
> The board is not entirely foolproof in this regard.
>
> - It can be host powered when connected via microUSB
> - It can be self-powered and host an device on microUSB
> - It can be self-powered and serve as a peripheral if you modify
>   a cable (cut VBUS) or the host is expecting this and has some
>   VBUS detection logic (most hosts will not have this)
>
> I just didn't want to encourage use as a peripheral, because it's not
> very foolproof. But I guess, DTS file will not stop anyone anyway.
>
> I'll change it to otg, and maybe leave a small note.

Your solution was great actually. I guess making a comment explaining
what you just did would be better though, so that no one is confused.

Maxime

--
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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