linux-kernel - Re: [PATCH v8 00/11] add USB GPIO based connection detection driver

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Message-ID: <1565077710.23705.21.camel@mhfsdcap03>
Date:   Tue, 6 Aug 2019 15:48:30 +0800
From:   Chunfeng Yun <chunfeng.yun@...iatek.com>
To:     Linus Walleij <linus.walleij@...aro.org>
CC:     Rob Herring <robh+dt@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Biju Das <biju.das@...renesas.com>,
        "Mark Rutland" <mark.rutland@....com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Adam Thomson <Adam.Thomson.Opensource@...semi.com>,
        Li Jun <jun.li@....com>,
        Badhri Jagan Sridharan <badhri@...gle.com>,
        "Heikki Krogerus" <heikki.krogerus@...ux.intel.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Min Guo <min.guo@...iatek.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-usb <linux-usb@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH v8 00/11] add USB GPIO based connection detection driver

On Mon, 2019-08-05 at 12:06 +0200, Linus Walleij wrote:
> On Wed, Jul 24, 2019 at 10:51 AM Chunfeng Yun <chunfeng.yun@...iatek.com> wrote:
> 
> > Because the USB Connector is introduced and the requirement of
> > usb-connector.txt binding, the old way using extcon to support
> > USB Dual-Role switch is now deprecated, meanwhile there is no
> > available common driver when use Type-B connector, typically
> > using an input GPIO to detect USB ID pin.
> 
> However while this was going on,
> drivers/extcon/extcon-fsa9480.c was merged and that detects
> not only GPIO on the USB port but multiplexed usecases such
> as UART over the USB micro PHY (and no that UART is not
> a USB UART, but an actual RX/TX over D-/D+).
> 
> That driver also measure a whole slew of funny resistance
> values on the ID pin, that is how it does its job.
I look into the spec of fsa9480, it indeed detect many USB accessories.
But this driver is used for simplest cases that only uses micro
receptacle with id-pin/vbus-pin

> 
> But for just "hey I'm plugged in" we can surely keep this
> ID on GPIO detection in the USB subsystem.
Sorry, you mean provide a common API? could you please describe more
clearer about your suggestion?


Introducing a single driver using usb_role_switch will help to keep
transparent for USB controller driver, no matter it uses type-c or micro

Thanks a lot
> 
> I just get a bit insecure about how we should ideally
> handle these "funny-PHY's".

> 
> Yours,
> Linus Walleij