linux-kernel - Re: [PATCH 11/11] arm64: dts: meson-g12a-x96-max: Enable USB

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Date:   Sat, 16 Mar 2019 23:07:01 +0100
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     Neil Armstrong <narmstrong@...libre.com>
Cc:     khilman@...libre.com, linux-amlogic@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 11/11] arm64: dts: meson-g12a-x96-max: Enable USB

Hi Neil,

On Sat, Mar 16, 2019 at 3:46 PM Neil Armstrong <narmstrong@...libre.com> wrote:
>
>
>
> Le 15/03/2019 22:50, Martin Blumenstingl a écrit :
> > Hi Neil,
> >
> > On Mon, Mar 11, 2019 at 10:58 AM Neil Armstrong <narmstrong@...libre.com> wrote:
> > [...]
> >> +&dwc2 {
> >> +       status = "okay";
> >> +};
> > your patch description states that this enables the "USB host ports"
> > but dwc2 is only used for peripheral mode (meaning: dr_mode =
> > "peripheral" or dr_mode = "otg").
> > do we still need to enable dwc2 in a host-only configuration?
>
> DWC2 is peripheral-only, but we can still manually switch one of the
> ports and use it as peripheral with a Type-A to Type-A cable, thus
> enabling dwc2.
thank you for the explanation!

> If the OTG capable PHYs was behind an USB Hub or directly connected to
> a device, we could disable dwc2, but for now this port is always tied
> to a physical Type-A or micro-USB connector.
>
> Maybe it would be sane to always enable dwc2, and disable it for specific
> boards only.
In case the port is connected to an USB hub we can add a comment to
the .dts to explain why dwc2 is being disabled. that way we don't need
a comment in each board.dts that it's enabled to support forced mode
switching.
in other words: I like this idea!


Regards
Martin