Re: [PATCH 3/3] ARM: dts: sunxi: add support for Anbernic RG-Nano

[Andre Przywara <andre.przywara@arm.com>]

On Fri, 30 Jun 2023 10:16:35 +0200
Maxime Ripard <mripard@kernel.org> wrote:

Hi,

> On Thu, Jun 29, 2023 at 08:34:10PM +0100, Andre Przywara wrote:
> > > > > +&usbphy {
> > > > > +	usb0_id_det-gpios = <&pio 5 6 GPIO_ACTIVE_HIGH>;  
> > 
> > Where is this pin connected to, in the USB-C connector? One of the CC
> > pins?
> >   
> > > > > +	status = "okay";    
> > > > 
> > > > So in the commit message you say "USB-C for power", but this here
> > > > describes a full featured USB port. So does that work? Can you use it as a
> > > > gadget, but also as a host?    
> > > 
> > > Yes, it's an OTG port with the ID pin pulled to ground.  
> > 
> > Do you mean both CC pins? IIRC this means it's hardwired as a
> > peripheral (UFP).
> > 
> > If I ignore the ID pin above, this looks like on the OrangePi Zero2 or
> > the MangoPi MQ-R. In those cases we put peripheral in the DT, as this
> > is what this connection seems to indicate. That *can* be used a host as
> > well, with the "right" cable, but it's not really a well supported
> > configuration, so we leave this up to people to change this locally,
> > should they really desire so.  
> 
> The ID pin above is exactly what makes "the right cable" works:
> depending on the state of the ID pin the controller will act either as a
> peripheral or a host. Dual-mode works just fine, so if the hardware
> supports it there's no reason not to enable it.

Mmmh, I think that's correct for an USB micro-B socket, but this is a
USB type C one. I don't think USB type C role switching can be easily
implemented with just a single GPIO, probably not even with two purely
digital GPIOs, as you would need some more clever voltage detection
circuitry.
For a simple connection via a USB-2.0 A<->C cable this probably doesn't
matter (as nothing happens to the CC pins?), and a USB-C thumb drive
probably would work as well, but I doubt those boards can properly
detect that automatically.

Chris, can you check how many pins from the type C connector are
actually used on the board? Can you follow the traces? Does it just
pull CC1 and CC2 to GND, via a resistor? Or are those pins somehow
connected to the SoC, or even a separate USB-C controller chip? Maybe
also worth checking if the stock OS can detect hosts or devices attached
automatically.

I am not really familiar with the USB type C situation in those
simplified USB-2.0-only setups, so if anyone can shed some light on
this, I'd be grateful.

Cheers,
Andre