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

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Message-ID: <20190409072237.fn2pe7ugtukdlnm2@flea>
Date:   Tue, 9 Apr 2019 09:22:37 +0200
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     linux-sunxi@...glegroups.com, Chen-Yu Tsai <wens@...e.org>,
        Rob Herring <robh+dt@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Mark Rutland <mark.rutland@....com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Jose Abreu <joabreu@...opsys.com>,
        "David S. Miller" <davem@...emloft.net>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Arend van Spriel <arend.vanspriel@...adcom.com>,
        Franky Lin <franky.lin@...adcom.com>,
        Hante Meuleman <hante.meuleman@...adcom.com>,
        Chi-Hsien Lin <chi-hsien.lin@...ress.com>,
        Wright Feng <wright.feng@...ress.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        Naveen Gupta <naveen.gupta@...ress.com>,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com,
        linux-wireless@...r.kernel.org,
        brcm80211-dev-list.pdl@...adcom.com,
        brcm80211-dev-list@...ress.com, linux-gpio@...r.kernel.org
Subject: Re: [PATCH 01/12] arm64: dts: allwinner: h6: Add Orange Pi 3 DTS

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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