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

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Message-ID: <ce0350a4-f7d9-3fdd-88ee-8cb827ecee2a@roeck-us.net>
Date:   Fri, 10 Mar 2017 15:41:08 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Mats Karrman <mats.dev.list@...il.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Oliver Neukum <oneukum@...e.com>, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org
Subject: Re: [PATCH v17 2/3] usb: USB Type-C connector class

On 03/10/2017 02:22 PM, Mats Karrman wrote:
> On 2017-03-08 14:58, Heikki Krogerus wrote:
>
>> On Tue, Mar 07, 2017 at 11:30:54PM +0100, Mats Karrman wrote:
>>> If I read Heikki's original suggestion I understand it like the DP driver would be
>>> responsible for AM specific USB PD/VDM communication. But wouldn't that lead
>>> to a lot of code duplication since the AM protocol is the same for all drivers of
>>> a kind?
>> No that's not what I mean. I'm still mixing your PD controller with
>> something else above, sorry about that. Your PD controller driver
>> should not ideally even need to be aware of Type-C connector, right?
>> It definitely does not need to do any USB PD communication.
>
> Right.
>
>> I would imagine you have on top of the DP controller, a mux (which
>> could be a DP/USB3 PHY like on Rockchip RK3399, discrete mux like
>> Pericom PI3USB30532, or something else), and a USB Type-C PHY or USB
>> PD controller. The bus would be tying the mux to the Type-C port (PHY
>> or PD controller) and its partner (note that it does not tie the mux
>> to the DP controller). Please correct me if I'm wrong about your
>> hardware.
>
> No, you're correct, a discrete mux and a fusb302.
>
>> Assuming that is how your board roughly looks like, the driver for the
>> mux would be the driver for the DP altmode devices. That driver would
>> be the one converting things like the Attention messages notifying
>> about HPD into toggling of GPIOs, or what ever is needed on your
>> board, etc.
>
> OK.
>
>> The actual PD communication with VDMs should be considered as just the
>> protocol, so we probable should have "protocol drivers". For example
>> DP alternate mode VDMs and communication will always be the same
>> despite of the hardware. The DP alternate mode "protocol driver" would
>> then be tied to the alternate mode device for the partner, and that
>> driver could have its own hooks for what ever is needed, like HPD
>> signal handling, configuration changes, whatever. In any case,
>> hopefully making things easy and straightforward for the "mux driver",
>> _so that it does not need to care about the actual PD communication_.
>
> I'm digesting your and Guenter's replies and patches.
> I will try getting something up and running too soon and hopefully the foggy parts will
> dissolve. As for now I find it a lot easier to grok Guenter's drivers than to see the
> advantages and/or disadvantages of an altmode bus :-)
>
> @Guenter: There _is_ interest for your fusb302 driver, thank you
>

Ok, I'll see what I need to do to publish it.

Guenter