linux-kernel - Re: [PATCH 0/3] USB Mux support for Chipidea

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Date:   Fri, 14 Jul 2017 14:27:09 -0700
From:   Stephen Boyd <stephen.boyd@...aro.org>
To:     Andy Gross <andy.gross@...aro.org>,
        Peter Chen <Peter.Chen@....com>, Peter Rosin <peda@...ntia.se>
Cc:     linux-usb@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Rob Clark <robdclark@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 0/3] USB Mux support for Chipidea

Quoting Stephen Boyd (2017-07-13 15:35:02)
> Quoting Peter Rosin (2017-07-11 22:04:46)
> > 
> > Maybe no need for a compatible update either, if it works to do something
> > like this in the DT?
> > 
> >         usb_switch: usb-switch {
> >                 compatible = "gpio-mux";
> >                 mux-gpios = <&pm8916_gpios 4 GPIO_ACTIVE_HIGH>,
> >                             <&pm8916_gpios XXX GPIO_ACTIVE_XXX>;
> >                 idle-state = <2>;
> >                 #mux-control-cells = <0>;
> >                 pinctrl-names = "default";
> >                 pinctrl-0 = <&usb_sw_sel_pm>;
> >         };
> > 
> > But I obviously know little about how things are wired and really works,
> > so that might be totally off...
> > 
> > Otherwise, maybe a generic mux-pinctrl driver would do the trick?
> > (compare with drivers/i2c/muxes/i2c-mux-pinctrl.c)
> > 
> 
> Agreed.

Testing looks good when I use the gpio-mux binding. The only thing I
noticed is that gpio-mux driver is requesting the gpio with
GPIOD_OUT_LOW. Is that intentional? I worry that may randomly mux the
D+/D- lines during probe if the gpio is asserted at probe time. It isn't
a problem for me right now, because the mux is power on defaulted to
have the gpio deasserted, but it may be a problem if the default
changes.