linux-kernel - Re: [PATCH v17 2/3] usb: USB Type-C connector class

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Message-ID: <20170307085753.GF6999@kuha.fi.intel.com>
Date:   Tue, 7 Mar 2017 10:57:53 +0200
From:   Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:     Peter Chen <peter.chen@....com>
Cc:     Peter Chen <hzpeterchen@...il.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Oliver Neukum <oneukum@...e.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        Roger Quadros <rogerq@...com>, Jun Li <jun.li@....com>
Subject: Re: [PATCH v17 2/3] usb: USB Type-C connector class

On Tue, Mar 07, 2017 at 01:36:29AM +0000, Peter Chen wrote:
> >On Mon, Mar 06, 2017 at 09:15:51AM +0800, Peter Chen wrote:
> >> > > What interface you use when you receive this event to handle
> >> > > dual-role switch? I am wonder if a common dual-role class is
> >> > > needed, then we can have a common user utility.
> >> > >
> >> > > Eg, if "data_role" has changed, the udev can echo "data_role" to
> >> > > /sys/class/usb-dual-role/role
> >> >
> >> > No. If the partner executes successfully for example DR_Swap
> >> > message, the kernel has to take care everything that is needed for
> >> > the role to be what ever was negotiated on its own. User space can't
> >> > be involved with that.
> >> >
> >>
> >> Would you give me an example how kernel handle this? How type-C event
> >> triggers role switch?
> >
> >On our boards, the firmware or EC (or ACPI) configures the hardware as needed
> >and also notifies the components using ACPI if needed. It's often not even possible to
> >directly configure the components/hardware for a particular role.
> >
> 
> You mean type-C trigger an ACPI event, and this ACPI event can notify related
> USB controller driver doing role switch?

No (firmware programs the dual-role hw/registers), but never mind.
That could be the case.

> If it is correct, there is a notifier between type-C
> and USB controller driver, how to define this notifier for non-ACPI platform? 

Once there is a platform with Type-C like that, the problem needs to
be solved. However..

> >I'm not commenting on Roger's dual role patch series, but I don't really think it should
> >be mixed with Type-C. USB Type-C and USB Power Delivery define their own ways
> >of handling the roles, and they are not limited to the data role only. Things like OTG
> >for example will, and actually can not be supported. With Type-C we will have
> >competing state machines compared to OTG. The dual-role framework may be
> >useful on systems that provide more traditional connectors, which possibly have the
> >ID-pin like micro-AB, and possibly also support OTG. It can also be something that
> >exist in parallel with the Type-C class, but there just can not be any dependencies
> >between the two.
> >
> 
> Yes, there are two independent things. But if the kernel doesn't have a notifier between
> type-C message sender (type-c class) and message receiver (like USB controller driver
> for role switch or other drivers for alternate mode message), we had to find some ways at
> userspace.

..what ever the solution is, it really can't rely on user space.


Thanks,

-- 
heikki