linux-kernel - Re: [PATCH 2/3] usb: add DT bindings for farady fotg2 host controller

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Date:   Sat, 22 Apr 2017 02:22:28 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Hans Ulli Kroll <ulli.kroll@...glemail.com>
Cc:     Rob Herring <robh@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Linux USB List <linux-usb@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH 2/3] usb: add DT bindings for farady fotg2 host controller

On Thu, Mar 30, 2017 at 8:31 PM, Hans Ulli Kroll
<ulli.kroll@...glemail.com> wrote:
>> On Tue, Feb 21, 2017 at 3:43 PM, Rob Herring <robh@...nel.org> wrote:
>> > On Fri, Feb 17, 2017 at 4:07 AM, Hans Ulli Kroll
>> > <ulli.kroll@...glemail.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@...glemail.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?

I hacked on it a bit and sent out. Hope you don't hate it too much.

> I prefer
> "faraday,fotg210-usb2"

I simply named it after the IP core name, which is just "faraday,fotg210".

> I've got rejected by Rob due the fact this is an dual role controller,
> which supports both host and device mode. And DT must reflect this desgn
> pattern.
>
> Currently I'm wrappingt my head around the design of the fsl-mph-dr-of.c
> driver to use this as a blueprint for the Faraday driver.

I don't know how much more of the dual-mode we need to reflect,
I guess it comes up in OTG mode since we don't parse the
host-only or device-only attributes (yet).

Yours,
Linus Walleij