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

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Message-ID: <2d2b411a-8a2c-85b9-5dc9-870c11801756@axentia.se>
Date:   Sat, 15 Jul 2017 10:33:47 +0200
From:   Peter Rosin <peda@...ntia.se>
To:     Stephen Boyd <stephen.boyd@...aro.org>,
        Andy Gross <andy.gross@...aro.org>,
        Peter Chen <Peter.Chen@....com>
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

On 2017-07-14 23:27, Stephen Boyd wrote:
> 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

Glad to hear it, I didn't really want a new driver so similar to the
mux-gpio driver...

> noticed is that gpio-mux driver is requesting the gpio with
> GPIOD_OUT_LOW. Is that intentional?

Not really intentional, it was just easy.

>                                     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.

It will not change, the only change I will accept is if the code in
mux-gpio can be arranged to request the gpios with the idle-state from
the start. But even then, the default idle-state (0) will not change.
So, you should be safe.

I will look at the new patches later.

Cheers,
Peter