linux-kernel - Re: [PATCH v6 15/28] ARM: tegra: Add usb-role-switch property to USB OTG ports

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Date:   Wed, 15 Dec 2021 20:16:26 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Jonathan Hunter <jonathanh@...dia.com>,
        David Heidelberg <david@...t.cz>,
        Svyatoslav Ryhel <clamor95@...il.com>,
        Anton Bambura <jenneron@...tonmail.com>,
        Antoni Aloy Torrens <aaloytorrens@...il.com>,
        Nikola Milosavljevic <mnidza@...look.com>,
        Ion Agorria <ion@...rria.com>,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        Ihor Didenko <tailormoon@...bler.ru>,
        Andreas Westman Dorcsak <hedmoo@...oo.com>,
        Maxim Schwalm <maxim.schwalm@...il.com>,
        Raffaele Tranquillini <raffaele.tranquillini@...il.com>,
        Jasper Korten <jja2000@...il.com>,
        Thomas Graichen <thomas.graichen@...il.com>,
        Stefan Eichenberger <stefan.eichenberger@...adex.com>,
        Stefan Agner <stefan@...er.ch>,
        Peter Geis <pgwipeout@...il.com>, devicetree@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 15/28] ARM: tegra: Add usb-role-switch property to USB
 OTG ports

15.12.2021 18:52, Thierry Reding пишет:
>>> On the other hand, at least Venice2 has a USB type A connector for this,
>>> so I'm not even sure how that would work. I vaguely recall that the
>>> Tegra20 Seaboard also had a USB type A and that it was possible to use
>>> it in device mode, but I don't how that would. Nor would it be correct
>>> to use the gpio-usb-b-connector compatible for that since, well, it's
>>> not USB type B.
>> I'm not sure whether it makes much sense to use OTG for USB type A
>> connectors, normally they should be fixed to host mode.
> My recollection is that those can be used in device mode as well. For
> example that USB type A port on Venice2 (same as for Seaboard) can be
> used for RCM, IIRC. It's possible that there's no way to detect what is
> connected, though, so this may not be proper OTG.

Sounds correct.

>>> I suspect that Apalis has a micro-B port, much like the Jetson TK1. My
>>> understanding is that OTG doesn't work on Jetson TK1 (which is why it's
>>> configured in "host" mode), so it'd be interesting to see if this can be
>>> made to work on Apalis.
>> Looks like the default Apalis carrier board has three type A connectors.
>>
>> https://www.toradex.com/products/carrier-board/ixora-carrier-board
> I'm wondering if the best thing would be to mark all of these as "host"
> for now and avoid making this look like something that it isn't. I don't
> think we've ever made OTG work on these boards, so perhaps we shouldn't
> assume that it works.

Marking them "host" should be correct, but that wasn't tested.

I assume that those "OTG" ports may default to the host mode.