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

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Message-ID: <648e2943-42f5-e07d-5bb4-f6fd8b38b726@redhat.com>
Date:   Wed, 16 Oct 2019 09:27:16 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     John Stultz <john.stultz@...aro.org>
Cc:     lkml <linux-kernel@...r.kernel.org>, Yu Chen <chenyu56@...wei.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Chunfeng Yun <chunfeng.yun@...iatek.com>,
        Felipe Balbi <balbi@...nel.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Jun Li <lijun.kernel@...il.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Linux USB List <linux-usb@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>
Subject: Re: [RFC][PATCH 2/3] usb: roles: Add usb role switch notifier.

Hi,

On 10/15/19 7:39 AM, John Stultz wrote:
> On Thu, Oct 3, 2019 at 1:51 PM Hans de Goede <hdegoede@...hat.com> wrote:
>> On 03-10-2019 22:37, John Stultz wrote:
>>> Fair point. I'm sort of taking a larger patchset and trying to break
>>> it up into more easily reviewable chunks, but I guess here I mis-cut.
>>>
>>> The user is the hikey960 gpio hub driver here:
>>>     https://git.linaro.org/people/john.stultz/android-dev.git/commit/?id=b06158a2d3eb00c914f12c76c93695e92d9af00f
>>
>> Hmm, that seems to tie the TypeC data-role to the power-role, which
>> is not going to work with role swapping.
> 
> Thanks again for the feedback here. Sorry for the slow response. Been
> reworking some of the easier changes but am starting to look at how to
> address your feedback here.
> 
>> What is controlling the usb-role-switch, and thus ultimately
>> causing the notifier you are suggesting to get called ?
> 
> The tcpm_mux_set() call via tcpm_state_machine_work()
> 
>> Things like TYPEC_VBUS_POWER_OFF and TYPEC_VBUS_POWER_ON
>> really beg to be modeled as a regulator and then the
>> Type-C controller (using e.g. the drivers/usb/typec/tcpm/tcpm.c
>> framework) can use that regulator to control things.
>> in case of the tcpm.c framework it can then use that
>> regulator to implement the set_vbus callback.
> 
> So I'm looking at the bindings and I'm not sure exactly how to tie a
> regulator style driver into the tcpm for this?
> Looking at the driver I just see this commented out bit:
>     https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/usb/typec/tcpm/tcpm.c#n3075
> 
> Do you happen to have a pointer to something closer to what you are describing?

Look at the tcpm_set_vbus implementation in drivers/usb/typec/tcpm/fusb302.c
you need to do something similar in your Type-C controller driver and
export the GPIO as as a gpio-controlled regulator and tie the regulator to
the connector.

Regards,

Hans