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

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Message-ID: <3fbd3fb9-1dc5-a46d-355b-f7c94b3c43ef@nvidia.com>
Date:   Tue, 8 Nov 2016 11:09:57 +0000
From:   Jon Hunter <jonathanh@...dia.com>
To:     Thierry Reding <thierry.reding@...il.com>
CC:     Peter De Schrijver <pdeschrijver@...dia.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 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.

Jon

-- 
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