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

[Chunfeng Yun]

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@xxxxxxxxxxxx> 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