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From: Linus Walleij <linus.walleij@linaro.org>
Date: Thu, 30 Mar 2017 01:16:35 +0200
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Subject: Re: [PATCH 2/3] usb: add DT bindings for farady fotg2 host controller
To: Rob Herring <robh@kernel.org>
Cc: Hans Ulli Kroll <ulli.kroll@googlemail.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        Linux USB List <linux-usb@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Mark Rutland <mark.rutland@arm.com>
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On Tue, Feb 21, 2017 at 3:43 PM, Rob Herring <robh@kernel.org> wrote:
> On Fri, Feb 17, 2017 at 4:07 AM, Hans Ulli Kroll
> <ulli.kroll@googlemail.com> wrote:
>> Hi Rob,
>>
>> On Wed, 15 Feb 2017, Rob Herring wrote:
>>
>>> On Wed, Feb 08, 2017 at 09:00:09PM +0100, Hans Ulli Kroll wrote:
>>> > This adds DT bindings for the Faraday FOTG2 host controller.
>>> >
>>> > Signed-off-by: Hans Ulli Kroll <ulli.kroll@googlemail.com>
>>> > ---
>>> >  Documentation/devicetree/bindings/usb/fotg2-host.txt | 15 +++++++++++++++
>>> >  1 file changed, 15 insertions(+)
>>> >  create mode 100644 Documentation/devicetree/bindings/usb/fotg2-host.txt
>>> >
>>> > diff --git a/Documentation/devicetree/bindings/usb/fotg2-host.txt b/Documentation/devicetree/bindings/usb/fotg2-host.txt
>>> > new file mode 100644
>>> > index 000000000000..4c07566a4bf5
>>> > --- /dev/null
>>> > +++ b/Documentation/devicetree/bindings/usb/fotg2-host.txt
>>> > @@ -0,0 +1,15 @@
>>> > +Faraday FOTG Host controller
>>> > +
>>> > +Required properties:
>>> > +
>>> > +- compatible: should be "faraday,fotg210-hcd"
>>>
>>> hcd as in "host controller driver"? Bindings describe h/w not drivers.
>>>
>>> It's an OTG controller or host controller?
>>>
>>
>> here only the host controller part used.
>>
>> faraday fotg2 is a dual role hcd/otg device and here is only the
>> host part used.
>
> Because you don't care about device mode or restricted by the IP
> configuration or SoC integration? The former is a user choice and
> shouldn't be part of DT. The latter should be implied by an SoC
> specific compatible string. Using only a compatible string for a
> licensed IP is not specific enough as vendors use differing versions
> and integrate them in different ways.

Hans can you add:

compatible = "cortina,gemini-fotg", "faraday,fotg210-hcd" or something
as composite compatible for our controller?

It's OK for the driver to only match on the latter for now, but for the
future it's nice for the driver to know what silicon it is on.

This is what I've done for most other Cortina/Gemini stuff.

Yours,
Linus Walleij