linux-kernel - Re: [PATCH] ARM: tegra: nyan: Mark all USB ports as host

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Date:   Tue, 8 Nov 2016 10:54:20 +0200
From:   Peter De Schrijver <pdeschrijver@...dia.com>
To:     Jon Hunter <jonathanh@...dia.com>
CC:     Thierry Reding <thierry.reding@...il.com>,
        Paul Kocialkowski <contact@...lk.fr>,
        <devicetree@...r.kernel.org>,
        Stephen Warren <swarren@...dotorg.org>,
        <linux-kernel@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        Alexandre Courbot <gnurou@...il.com>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] ARM: tegra: nyan: Mark all USB ports as host

On Mon, Nov 07, 2016 at 02:09:31PM +0000, Jon Hunter wrote:
> 
> On 07/11/16 13:28, Thierry Reding wrote:
> > * PGP Signed by an unknown key
> > 
> > On Sun, Sep 18, 2016 at 12:28:52PM +0200, Paul Kocialkowski wrote:
> >> Nyan boards only have host USB ports (2 external, 1 internal), there is
> >> no OTG-enabled connector.
> >>
> >> Signed-off-by: Paul Kocialkowski <contact@...lk.fr>
> >> ---
> >>  arch/arm/boot/dts/tegra124-nyan.dtsi | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > Where is this information coming from? I don't have one of the Nyans
> > myself, but one of the Tegra132 devices I have, which I think was
> > derived from one of the Nyans uses one of the external host ports as
> > forced recovery port, for which it would need OTG.
> > 
> > I suspect that the way to get U-Boot onto the Nyans is via tegrarcm?
> > In that case I think one of the ports must be OTG.
> 
> It is true that the port on the back on the nyan-big can be used with
> recovery mode. I was thinking that this is not a true OTG port as it is
> just a 4-pin type A socket and does not have an ID pin. Thinking some
> more about this the USB spec does include a "Host Negotiation Protocol
> (HNP)" that allows a host and device to swap roles and so keeping it as
> OTG seems valid afterall.

I don't think the bootrom implements that though. I expect recovery mode
to just program the controller in device mode, without performing any
negotiation.

Peter.