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

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Date:   Fri, 10 Mar 2017 23:22:16 +0100
From:   Mats Karrman <mats.dev.list@...il.com>
To:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        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 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

BR // Mats