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

From: Guenter Roeck <linux@roeck-us.net>
To: Peter Chen <peter.chen@nxp.com>,
	Heikki Krogerus <heikki.krogerus@linux.intel.com>
Cc: Peter Chen <hzpeterchen@gmail.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: Wed, 8 Mar 2017 06:44:47 -0800	[thread overview]
Message-ID: <055d6289-c728-30bb-279e-65e08be5e538@roeck-us.net> (raw)
In-Reply-To: <HE1PR04MB145053A5B07D66602ADEAB928B2E0@HE1PR04MB1450.eurprd04.prod.outlook.com>

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/).

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