linux-kernel - Re: [PATCH v2 2/2] usb: dwc3: support clocks and resets for DWC3 core

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Date:   Fri, 27 Apr 2018 13:40:01 -0500
From:   Rob Herring <robh@...nel.org>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Linux USB List <linux-usb@...r.kernel.org>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Roger Quadros <rogerq@...com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Jassi Brar <jaswinder.singh@...aro.org>,
        Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>,
        DTML <devicetree@...r.kernel.org>,
        Felipe Balbi <balbi@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v2 2/2] usb: dwc3: support clocks and resets for DWC3 core

On Fri, Apr 27, 2018 at 11:20 AM, Masahiro Yamada
<yamada.masahiro@...ionext.com> wrote:
> Hi Rob,
>
>
> 2018-04-26 0:21 GMT+09:00 Rob Herring <robh@...nel.org>:
>
>>> diff --git a/Documentation/devicetree/bindings/usb/dwc3.txt b/Documentation/devicetree/bindings/usb/dwc3.txt
>>> index 0dbd308..feb1cc33 100644
>>> --- a/Documentation/devicetree/bindings/usb/dwc3.txt
>>> +++ b/Documentation/devicetree/bindings/usb/dwc3.txt
>>> @@ -7,6 +7,27 @@ Required properties:
>>>   - compatible: must be "snps,dwc3"
>>>   - reg : Address and length of the register set for the device
>>>   - interrupts: Interrupts used by the dwc3 controller.
>>> + - clock-names: should contain "ref", "bus_early", "suspend"
>>> + - clocks: list of phandle and clock specifier pairs corresponding to
>>> +           entries in the clock-names property.
>>> + - resets: a single pair of phandle and reset specifier
>>
>> This should be optional as some SoCs don't have separate, s/w controlled
>> resets of modules.
>
> OK.  I will move resets to optional property.
>
>
> Please let ask a question.
>
>
> The number of clocks should be the same across SoCs.
> (Even if there is no s/w control for clocks,
> we should input something such as clk-fixed-rate.)

I guess if there's really not s/w control, then the number may vary,
but let's worry about that when someone has that problem.

> On the other hand, the number of resets can be different
> across SoCs.  If there is no s/w control for resets,
> we can make it optional.   (optional = 1 or 0 reset)
>
> Is this what you mean?

Yes. I think it's just more common to not have a reset than not have clocks.

> If we had something like reset-nop (or reset-dummy)
> in case no s/w control, we would be able to input something.
> I am not sure if this is the right thing, though.

I don't think we should require things if they are not needed.

Rob