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

From: Peter Chen <hzpeterchen@gmail.com>
To: Guenter Roeck <linux@roeck-us.net>
Cc: Peter Chen <peter.chen@nxp.com>,
	Heikki Krogerus <heikki.krogerus@linux.intel.com>,
	Greg KH <gregkh@linuxfoundation.org>,
	Felipe Balbi <felipe.balbi@linux.intel.com>,
	Oliver Neukum <oneukum@suse.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
	Roger Quadros <rogerq@ti.com>, Jun Li <jun.li@nxp.com>
Subject: Re: [PATCH v17 2/3] usb: USB Type-C connector class
Date: Thu, 9 Mar 2017 10:00:31 +0800	[thread overview]
Message-ID: <20170309020031.GA4623@b29397-desktop> (raw)
In-Reply-To: <055d6289-c728-30bb-279e-65e08be5e538@roeck-us.net>

On Wed, Mar 08, 2017 at 06:44:47AM -0800, Guenter Roeck wrote:
> On 03/07/2017 10:50 PM, Peter Chen wrote:
> >
> >>>>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.
> >>>
> >>
> >>... and, at least for our application, using extcon for the necessary notifications works
> >>just fine.
> >>
> >
> >I see, that means you have a hardware signal to notify role switch.
> >
> 
> In our case the Type-C protocol manager (including alternate mode handling)
> is implemented in an EC. The EC signals the extcon-cros_ec driver, which
> in turn signals the phy driver as well as the DP driver. The Type-C class
> is orthogonal; extcon-cros_ec will also register with the Type-C class code
> once that is upstream.
> 
> As mentioned earlier, using extcon for signaling was the most convenient means
> for us to pass events around. I am more than open to change it to a bus,
> if that can be made to work - we'd have to keep in mind though that this code
> already works without Type-C infrastructure and is for the most part already
> upstream (the rk3399 code it ties into is upstream, and extcon-cros_ec has been
> submitted as https://patchwork.kernel.org/patch/9583045/).
> 

I am clear your implementation now, thank, Guenter.

> As for to how to handle alternate mode if the Type-C protocol manager
> (TCPM) is implemented in the kernel - I have not yet implemented it yet,
> but my thinking goes along the line described by Heikki in his last e-mail.
> 
> Note that we also have a kernel driver for FUSB302 which ties into my tcpm
> driver. I'll have to check if that is public yet and if I or someone
> else can publish it if there is interest.
> 
> Guenter
> 

-- 

Best Regards,
Peter Chen