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

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Message-ID: <f2236442-111d-cd84-fc47-0737df71cf3a@redhat.com>
Date:   Fri, 18 Oct 2019 10:06:18 +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 18-10-2019 07:55, John Stultz wrote:
> On Wed, Oct 16, 2019 at 12:27 AM Hans de Goede <hdegoede@...hat.com> wrote:
>> 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.
> 
> Thanks for the suggestion, I really appreciate it! One more question
> though, since I'm using the tcpci_rt1711h driver, which re-uses the
> somewhat sparse tcpci.c implementation, would you recommend trying to
> add generic regulator support to the tcpci code or trying to extend
> the implementation somehow allow the tcpci_rt1711h driver replace just
> the set_vbus function?

I have the feeling that this is more of a question for Heikki.

My first instinct is: if you are using tcpci can't you put all
the hacks you need for the usb connection shared between hub
and type-c in your firmware ?

Regards,

Hans