Message-ID: <20170913161728.GA436@roeck-us.net>
Date:   Wed, 13 Sep 2017 09:17:28 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     Rob Herring <robh@...nel.org>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        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" <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 List <linux-usb@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 10/11] staging: typec: fusb302: Hook up mux support
 using tcpc_gen_mux support

On Wed, Sep 13, 2017 at 05:48:25PM +0200, Hans de Goede wrote:
> Hi,
> 
> On 13-09-17 17:07, Rob Herring wrote:
> >On Wed, Sep 13, 2017 at 9:06 AM, Hans de Goede <hdegoede@...hat.com> wrote:
> >>Hi,
> >>
> >>
> >>On 13-09-17 15:38, Rob Herring wrote:
> >>>
> >>>On Wed, Sep 13, 2017 at 3:56 AM, Hans de Goede <hdegoede@...hat.com>
> >>>wrote:
> >>>>
> >>>>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.
> >>>
> >>>
> >>>Thinking about this some more, the mux(es) should be its own node(s).
> >>>Then the question is where to put the nodes.
> >>
> >>
> >>Right, the mux will be its own node per
> >>Documentation/devicetree/bindings/mux/mux-controller.txt
> >>the bindings bit this patch is adding is only adding phandles pointing
> >>to that mux-node as the fusb302 "consumes" the mux functionality.
> >>
> >>So as such (the fusb302 is the component which should control the mux)
> >>I do believe that the bindings this patch adds are correct.
> >
> >Humm, that's not how the mux binding works. The mux controller is what
> >drives the mux select lines and is the provider. The consumer is the
> >mux device itself. What decides the mux state is determined by what
> >you are muxing, not which node has mux-controls property.
> >
> >By putting mux-controls in fusb302 node, you are saying fusb302 is a
> >mux (or contains a mux).
> >
> >
> >>>>As for putting it in a type-C connector node, currently we do not have
> >>>>such
> >>>>a node,
> >>>
> >>>
> >>>Well, you should. Type-C connectors are certainly complicated enough
> >>>that we'll need one. Plus we already require connector nodes for
> >>>display outputs, so what do we do once you add display muxing?
> >>
> >>
> >>An interesting question, I'm working on this for x86 + ACPI boards actually,
> >>not a board using DT I've been adding DT bindings docs for device-properties
> >>I use because that seems like the right thing to do where the binding is
> >>obvious
> >>(which I believe it is in this case as the fusb302 is the mux consumer) and
> >>because the device-property code should work the same on x86 + ACPI
> >>(where some platform-specific drivers attach the device properties) and
> >>on e.g. ARM + DT.
> >>
> >>The rest should probably be left to be figured out when an actual DT
> >>using device using the fusb302 or another Type-C controller shows up.
> >
> >Well this is a new one (maybe, I suppose others have sneaked by). If
> >ACPI folks want to use DT bindings, then what do I care. But I have no
> >interest in reviewing ACPI properties. The whole notion of sharing
> >bindings between DT and ACPI beyond anything trivial is flawed IMO.
> >The ptifalls have been discussed multiple times before, so I'm not
> >going to repeat them here.
> 
> Ok, so shall I just drop the Documentation/devicetree/bindings/usb/fcs,fusb302.txt
> part of this patch then ?
> 
FWIW, Android (where the fusb302 driver is coming from) does use dt.
On the other side I assume they won't jump on the new mux handling
immediately. I won't have time to look into it myself, so whatever
is done here may not match the "real" dt use case. Given that, maybe
it does make sense to drop the bindings part and revisit once it
becomes relevant.

Guenter

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