linux-kernel - Re: [PATCH] arm64: dts: ti: k3-am69-sk: Add USB SuperSpeed support

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Message-ID: <o37g5m3qvod4mydnjytyubobmvit7zjmh5xhv6jxjze3reiqct@wkwm36yvftyr>
Date: Wed, 4 Dec 2024 10:31:50 +0530
From: s-vadapalli <s-vadapalli@...com>
To: Enric Balletbo i Serra <eballetb@...hat.com>
CC: s-vadapalli <s-vadapalli@...com>, Nishanth Menon <nm@...com>,
        "Vignesh
 Raghavendra" <vigneshr@...com>,
        Tero Kristo <kristo@...nel.org>, Rob Herring
	<robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley
	<conor+dt@...nel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, Dasnavis Sabiya
	<sabiya.d@...com>
Subject: Re: [PATCH] arm64: dts: ti: k3-am69-sk: Add USB SuperSpeed support

On Tue, Dec 03, 2024 at 04:29:02PM +0100, Enric Balletbo i Serra wrote:
> Hi,
> 
> On Thu, Nov 28, 2024 at 10:58 AM s-vadapalli <s-vadapalli@...com> wrote:
> >
> > On Thu, Nov 28, 2024 at 10:47:42AM +0100, Enric Balletbo i Serra wrote:
> > > Hi,
> >
> > [...]
> >
> > > So I changed the dr_mode to otg instead of host and tried to configure
> > > a usb mass storage gadget but unfortunately didn't work, but this
> > > could be a driver problem, I got the following error
> > >
> > >   UDC core: g1: couldn't find an available UDC
> > >
> > > As the devicetree should describe the hardware, and as far as I can
> > > see it should support the type-c port act as a gadget, I'm fine with
> > > changing the dr_mode, unless anyone have more information about this,
> > > the thing that makes me think a bit more is that, in the TI kernel
> > > this is set to host, so I'm wondering if I'm missing something or is
> > > just that was never tested.
> >
> > Are all interfaces (Type-A and Type-C) functional as Host when the
> > dr_mode is set to "otg"? (Do USB devices connected to the interfaces
> > enumerate on AM69-SK?) If yes, then it could be a DIP Switch setting
> > that is related to OTG mode of operation or a USB-C Mux that needs to be
> > configured.
> >
> 
> Yes, all interfaces (Type-A and Type-C) are functional as host when
> the dr_mode is set to "otg". Looking at SK-AM69 Processor Start Kit
> User's Guide (Rev. A) [1] I don't see any DIP Switch related to the
> OTG  mode. Looks like the type-c connector connects directly to the
> SoC through a USB HUB (TUSB4041).
> 
> [1] https://www.ti.com/lit/ug/spruj70a/spruj70a.pdf?ts=1733215039014

In that case, please post the patch setting "dr_mode" to "otg". As to
why "peripheral"/"gadget" operation doesn't work could be addressed
separately and seems to be independent of the device-tree. The reason
for suggesting "otg" instead of "host" is to ensure that the device-tree
describes the Hardware. Since "host" mode is still functional with
"dr_mode" set to "otg", at-least for the use-cases that you have in mind,
I believe that "otg" should be acceptable.

Regards,
Siddharth.