linux-kernel - Re: [PATCH 0/2] platform/x86: intel_cht

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Message-ID: <be150dea-7c55-f0f4-501f-5818e0b3873c@redhat.com>
Date:   Mon, 25 Feb 2019 20:14:55 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:     Andy Shevchenko <andy@...radead.org>,
        Darren Hart <dvhart@...radead.org>,
        platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] platform/x86: intel_cht_int33fe: Start using software
 nodes

Hi,

On 25-02-19 16:48, Heikki Krogerus wrote:
> On Fri, Feb 22, 2019 at 05:31:32PM +0100, Hans de Goede wrote:
>> Hi,
>>
>> On 2/19/19 12:59 PM, Heikki Krogerus wrote:
>>> Hi guys,
>>>
>>> The software nodes support node hierarchy. By using them with fusb302
>>> we can add a separate fwnode also for the USB connector as a child of
>>> fusb302. We can then use the "standard" USB connector device
>>> properties with the connector node, and stop using the deprecated
>>> fusb302 specific properties.
>>>
>>> Since the goal is to ultimately move to the software node API from the
>>> old device property API, converting also max17047 in this series.
>>>
>>> If you test this now (before v5.1-rc1 is out), then the series depends
>>> Greg's latest usb-next:
>>> https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git/log/?h=usb-next
>>>
>>> and on a patch in Rafael's latest linux-next branch:
>>> https://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git/commit/?h=linux-next&id=344798206f171c5abea7ab1f9762fa526d7f539d
>>
>> Interesting series, I like the direction this is heading in.
>>
>> Question, I currently have this hack to test DP over Type-C on the
>> GPD-pocket / GPD-win:
>>
>> https://github.com/jwrdegoede/linux-sunxi/commit/f481b7032030dcdda1ccc39875eb59f996d3e775
>>
>> Do this properly we need to add alt-modes support for usb-c-connector nodes to:
>> Documentation/devicetree/bindings/connector/usb-connector.txt
> 
> Yes, this is a topic I wanted to talk about.
> 
>> Do you have any ideas for what the binding this should look like, we need to
>> specify a svid, mode and vdo tripple in this case. Maybe use an u32 array
>> with 3, 6, 9, ... entries depending on how much alt-modes the fwnode needs to
>> specify ?
> 
> My idea was to use sub-nodes, i.e. every alt mode a connector supports
> would need to have its own child node under the connector node. Those
> sub-nodes could then have a device property "svid" and another device
> property "vdo", etc.

Right, after sending this mail I realized myself that using child-nodes
to group the svid and vdo together was the right answer. So we
could add child-nodes with a binding like this:

Optionally an "usb-c-connector" can have child nodes, describing
supported alt-modes.

Required properties for usb-c-connector altmode child-nodes:
compatible:  "usb-type-c-altmode"
svid:        integer, Standard or Vendor ID for the altmode (u16 stored in an u32) property and an u32
vdo:         integer, Vendor Data Object, VDO describing the altmode capabilies, SVID specific

I'm not sure if we also need to specify the altmode index here, or
we simple assign each alt-mode an index while enumerating?

> I think that approach would be OK in DT, and we can now support it also
> with the software nodes, and even in ACPI there are now something
> called "data nodes" which can be used for this purpose.

Ack.

> There are some questions though. That "USB connector" node description
> relies on OF graph, so should we just extend those "endpoint" nodes
> (which are sub-nodes), or should be still have dedicated sub-nodes for
> the alt modes? I think we may need dedicated nodes for the alt modes
> in any case if we choose to use this approach.

Right I'm thinking dedicated nodes for the alt modes.

I guess an alt-mode could have a port child-node to point to say the
DisplayPort pins / mux connection ?  I'm not entirely sure how the graph
stuff will work here, but I guess that from a DT pov it will be desirable
to be able to describe where the datalines for the alt-mode come from,
maybe in combination with what the "mux/select" value is for the mux ???

Regards,

Hans