linux-kernel - Re: [PATCH v2 10/11] staging: typec: fusb302: Hook up mux support using tcpc_gen

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Date:   Wed, 13 Sep 2017 10:56:49 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Rob Herring <robh@...nel.org>
Cc:     MyungJoo Ham <myungjoo.ham@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        Peter Rosin <peda@...ntia.se>,
        Mathias Nyman <mathias.nyman@...el.com>,
        linux-kernel@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        devel@...verdev.osuosl.org,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Sathyanarayanan Kuppuswamy Natarajan <sathyaosid@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, Mark Rutland <mark.rutland@....com>,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v2 10/11] staging: typec: fusb302: Hook up mux support
 using tcpc_gen_mux support

Hi,

On 13-09-17 00:20, Rob Herring wrote:
> On Tue, Sep 05, 2017 at 06:42:20PM +0200, Hans de Goede wrote:
>> Add mux support to the fusb302 driver, call devm_tcpc_gen_mux_create()
>> to let the generic tcpc_mux_dev code create a tcpc_mux_dev for us.
>>
>> Also document the mux-names used by the generic tcpc_mux_dev code in
>> our devicetree bindings.
>>
>> Cc: Rob Herring <robh+dt@...nel.org>
>> Cc: Mark Rutland <mark.rutland@....com>
>> Cc: devicetree@...r.kernel.org
>> Signed-off-by: Hans de Goede <hdegoede@...hat.com>
>> ---
>>   Documentation/devicetree/bindings/usb/fcs,fusb302.txt |  3 +++
>>   drivers/staging/typec/fusb302/fusb302.c               | 11 ++++++++++-
>>   2 files changed, 13 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/devicetree/bindings/usb/fcs,fusb302.txt b/Documentation/devicetree/bindings/usb/fcs,fusb302.txt
>> index 472facfa5a71..63d639eadacd 100644
>> --- a/Documentation/devicetree/bindings/usb/fcs,fusb302.txt
>> +++ b/Documentation/devicetree/bindings/usb/fcs,fusb302.txt
>> @@ -6,6 +6,9 @@ Required properties :
>>   - interrupts             : Interrupt specifier
>>   
>>   Optional properties :
>> +- mux-controls           : List of mux-ctrl-specifiers containing 1 or 2 muxes
>> +- mux-names              : "type-c-mode-mux" when using 1 mux, or
>> +                           "type-c-mode-mux", "usb-role-mux" when using 2 muxes
> 
> I'm not sure this is the right place for this. The mux is outside the
> FUSB302. In a type-C connector node or USB phy node would make more
> sense to me.

The mux certainly does not belong in the USB phy node, it sits between the USB PHY
and the Type-C connector and can for example also mux the Type-C pins to a Display
Port PHY.

As for putting it in a type-C connector node, currently we do not have such a node,
the closest thing we do have to a node describing it is actually the fusb302 node
itself. E.g. it may also contain a regulator to turn Vbus on / off (already there
in the code, but I forgot to document this when I added the missing DT bindings
doc for the fusb302 with a previous patch).

Also these properties:

>>   - fcs,max-sink-microvolt : Maximum voltage to negotiate when configured as sink
>>   - fcs,max-sink-microamp  : Maximum current to negotiate when configured as sink
>>   - fcs,max-sink-microwatt : Maximum power to negotiate when configured as sink

Have more to do with the charger-IC used (which determines the limits) then with
the fusb302 itself, but the fusb302 needs to know these as it negotiates the limits.

Likewise the fusb302 negotiates how the data pins will be used and thus to which pins
on the SoC the mux should mux the data pins.

TL;DR: The fusb302 does all the negotiation and ties all the Type-C connected
ICs together, so this seems like the right place for it (it certainly is the
natural place to put these from a driver code pov).

Regards,

Hans