Re: [RFC][PATCH 2/3] usb: roles: Add usb role switch notifier.

From: Hans de Goede <hdegoede@redhat.com>
To: John Stultz <john.stultz@linaro.org>
Cc: lkml <linux-kernel@vger.kernel.org>,
	Yu Chen <chenyu56@huawei.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Rob Herring <robh+dt@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Heikki Krogerus <heikki.krogerus@linux.intel.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Chunfeng Yun <chunfeng.yun@mediatek.com>,
	Felipe Balbi <balbi@kernel.org>,
	Andy Shevchenko <andy.shevchenko@gmail.com>,
	Jun Li <lijun.kernel@gmail.com>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Linux USB List <linux-usb@vger.kernel.org>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
	<devicetree@vger.kernel.org>
Subject: Re: [RFC][PATCH 2/3] usb: roles: Add usb role switch notifier.
Date: Fri, 18 Oct 2019 21:59:51 +0200	[thread overview]
Message-ID: <7ea7824f-abc2-4cf6-720a-3668b6286781@redhat.com> (raw)
In-Reply-To: <CALAqxLWE-8YkYmrKoP6-+2xherwsGZ8-CeUyOFe9YPQj6EuSpg@mail.gmail.com>

Hi,

On 18-10-2019 21:53, John Stultz wrote:
> On Fri, Oct 18, 2019 at 12:30 PM Hans de Goede <hdegoede@redhat.com> wrote:
>> Looking at drivers/usb/typec/tcpm/tcpci.c: tcpci_set_vconn I see that
>> there is a data struct with vendor specific callbacks and that the
>> drivers/usb/typec/tcpm/tcpci_rt1711h.c implements that.
>>
>> So you may want something similar here. But things are tricky here,
>> because when nothing is connected you want to provide Vbus for
>> the USB-A ports, which means that if someone then connects a
>> USB-A to C cable to connect the board to a PC (switching the port
>> to device mode) there will be a time when both sides are supplying
>> 5V if I remember the schedule correctly.
> 
> Ok. Thanks for the pointer, I'll take a look at that to see if I can
> get it to work.
> 
>> I think that the original hack might not be that bad, the whole hw
>> design seems so, erm, broken, that you probably cannot do proper
>> roleswapping anyways.  So just tying Vbus to host mode might be
>> fine, the question then becomes again how can some other piece
>> of code listen to the role-switch events...
> 
> So, at least in the current approach (see the v3 series), I've
> basically set the hub driver as an role-switch intermediary, sitting
> between the calls from the tcpm to the dwc3 driver. It actually works
> better then the earlier notifier method (which had some issues with
> reliably establishing the initial state on boot).  Does that approach
> work for you?

That sounds like it might be a nice solution. But I have not seen the
code, I think I was not Cc-ed on v3. Do you have a patchwork or
lore.kernel.org link for me?

Regards,

Hans