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

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Message-ID: <1478610158.853.1.camel@paulk.fr>
Date:   Tue, 08 Nov 2016 14:02:38 +0100
From:   Paul Kocialkowski <contact@...lk.fr>
To:     Jon Hunter <jonathanh@...dia.com>,
        Thierry Reding <thierry.reding@...il.com>
Cc:     Peter De Schrijver <pdeschrijver@...dia.com>,
        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

Le mardi 08 novembre 2016 à 11:09 +0000, Jon Hunter a écrit :
> On 08/11/16 11:07, Thierry Reding wrote:
> > 
> > * PGP Signed by an unknown key
> > 
> > On Tue, Nov 08, 2016 at 09:47:42AM +0000, Jon Hunter wrote:
> > > 
> > > 
> > > On 08/11/16 08:54, Peter De Schrijver wrote:
> > > > 
> > > > On Mon, Nov 07, 2016 at 02:09:31PM +0000, Jon Hunter wrote:
> > > > > 
> > > > > 
> > > > > On 07/11/16 13:28, Thierry Reding wrote:
> > > > > > 
> > > > > > > 
> > > > > > > Old 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.
> > > 
> > > I am not talking about the bootrom and I would not expect the bootrom to
> > > do that. However, the kernel could.
> > 
> > Either way, configuring the controller in device mode is enough to make
> > the host detect it, otherwise tegrarcm wouldn't work.
> > 
> > From the point of view of the binding I think "otg" is the most accurate
> > option because we know that the controller can operate in both modes. If
> > it currently doesn't or how exactly switching modes is done is outside
> > the scope of this property.
> > 
> > Is everyone okay with just dropping this patch?
> 
> Fine with me.

Same here.

-- 
Paul Kocialkowski, developer of low-level free software for embedded devices

Website: https://www.paulk.fr/
Coding blog: https://code.paulk.fr/
Git repositories: https://git.paulk.fr/ https://git.code.paulk.fr/
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