linux-kernel - Re: [PATCH v10 2/7] usb: mux: add generic code for dual role port mux

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Date:	Mon, 6 Jun 2016 10:05:07 +0800
From:	Peter Chen <hzpeterchen@...il.com>
To:	Lu Baolu <baolu.lu@...ux.intel.com>
Cc:	Jun Li <jun.li@....com>,
	"felipe.balbi@...ux.intel.com" <felipe.balbi@...ux.intel.com>,
	Mathias Nyman <mathias.nyman@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Lee Jones <lee.jones@...aro.org>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Roger Quadros <rogerq@...com>
Subject: Re: [PATCH v10 2/7] usb: mux: add generic code for dual role port mux

On Sun, Jun 05, 2016 at 04:46:55PM +0800, Lu Baolu wrote:
> Hi,
> 
> On 06/05/2016 04:33 PM, Jun Li wrote:
> >> Port mux is part of dual role switch, but not the whole thing.
> >> > 
> >> > Dual role switch includes at least below things:
> >> >  - ID or type-C event detection
> >> >  - port mux
> >> >  - VBUS management
> >> >  - start/stop host/device controllers
> >> > 
> >> > An OTG/Dual-role framework can be used to keep all these things run
> >> > together with an internal state machine. But it's not duplicated with a
> >> > generic framework for port mux and the port mux drivers.
> >> > 
> >>> > > Your
> >>> > > case is just like Renesas case, which uses two different drivers
> >>> > > between peripheral and host[1].
> >> > 
> >> > In my case, the port mux devices are physical devices and they can be
> >> > controlled through GPIO pins or device registers. They are independent of
> >> > both peripheral and host controllers.
> >> > 
> > I also think current OTG/Dual role framework can support your case, if you
> > find there is any limitation of it which can't meet your requirement, we
> > should improve it, Roger also provide an example of dual role switch with
> > USB3 based on his OTG core.
> 
> Why do we need an OTG framework to support a device driver?

Just like you said above, OTG framework can manage role switch, the
role switch may need to start or stop host/gadget driver according to
different hardware signals or user input.

> Is it something like a bus or class driver?

The DRD/OTG framework uses the same device structure with the caller,
the caller can be a dual-role controller driver (like dwc3, chipidea,
etc), or a separate switch driver which like your mux port driver.

-- 

Best Regards,
Peter Chen