linux-kernel - Re: [RFC][PATCH v2 4/5] dt-bindings: usb: dwc3: of-simple: add compatible for HiSi

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Message-ID: <CALAqxLUbh7_PkOwh9NrS_+sgLDZMHndbp44jVQkB=WqOhKUotA@mail.gmail.com>
Date:   Mon, 14 Oct 2019 20:57:22 -0700
From:   John Stultz <john.stultz@...aro.org>
To:     Rob Herring <robh@...nel.org>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Felipe Balbi <balbi@...nel.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Mark Rutland <mark.rutland@....com>,
        Yu Chen <chenyu56@...wei.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Chunfeng Yun <chunfeng.yun@...iatek.com>,
        Linux USB List <linux-usb@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>
Subject: Re: [RFC][PATCH v2 4/5] dt-bindings: usb: dwc3: of-simple: add
 compatible for HiSi

On Fri, Oct 11, 2019 at 8:51 AM Rob Herring <robh@...nel.org> wrote:
>
> On Mon, Oct 07, 2019 at 04:00:24PM -0700, John Stultz wrote:
> > On Mon, Oct 7, 2019 at 2:11 PM Rob Herring <robh+dt@...nel.org> wrote:
> > >
> > > On Mon, Oct 7, 2019 at 2:07 PM John Stultz <john.stultz@...aro.org> wrote:
> > > >
> > > > On Mon, Oct 7, 2019 at 11:38 AM Rob Herring <robh+dt@...nel.org> wrote:
> > > > >
> > > > > On Mon, Oct 7, 2019 at 12:56 PM John Stultz <john.stultz@...aro.org> wrote:
> > > > > >
> > > > > > Add necessary compatible flag for HiSi's DWC3 so
> > > > > > dwc3-of-simple will probe.
> > > > > >
> > > > > > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > > > > > Cc: Felipe Balbi <balbi@...nel.org>
> > > > > > Cc: Andy Shevchenko <andy.shevchenko@...il.com>
> > > > > > Cc: Rob Herring <robh+dt@...nel.org>
> > > > > > Cc: Mark Rutland <mark.rutland@....com>
> > > > > > Cc: Yu Chen <chenyu56@...wei.com>
> > > > > > Cc: Matthias Brugger <matthias.bgg@...il.com>
> > > > > > Cc: Chunfeng Yun <chunfeng.yun@...iatek.com>
> > > > > > Cc: linux-usb@...r.kernel.org
> > > > > > Cc: devicetree@...r.kernel.org
> > > > > > Signed-off-by: John Stultz <john.stultz@...aro.org>
> > > > > > ---
> > > > > > v2: Tweaked clock names as clk_usb3phy_ref didn't seem right.
> > > > > > ---
> > > > > >  .../devicetree/bindings/usb/hisi,dwc3.txt     | 52 +++++++++++++++++++
> > > > > >  1 file changed, 52 insertions(+)
> > > > > >  create mode 100644 Documentation/devicetree/bindings/usb/hisi,dwc3.txt
> > > > >
> > > > > Can you make this a schema.
> > > >
> > > > Sorry, I'm not sure exactly what you're asking. I'm guessing from
> > > > grepping around you want the bindings in yaml instead (I see a few
> > > > examples)?
> > >
> > > Yes.
> > >
> > > > Is there some pointer to documentation? The
> > > > Documentation/devicetree/bindings/writing-bindings.txt file doesn't
> > > > seem to say much on it.
> > >
> > > You mean Documentation/devicetree/writing-schemas.rst? There's that
> > > and Documentation/devicetree/bindings/example-schema.yaml which has a
> > > bunch of annotations on what each part means.
> >
> > Ah! Sorry for missing that. Thanks for the pointer, though I may get
> > away with dropping this one.
> >
> > > > > If it's only clocks and resets for the wrapper node, just make this
> > > > > all one node.
> > > >
> > > > Just to make sure I'm following, you're suggesting I put all the
> > > > clocks/resets in the dwc3 node (renamed to usb for the node name) and
> > > > not add the wrapper?
> > >
> > > Yes.
> > >
> > > > I'll have to see if that's possible. The generic dwc3 binding wants 3
> > > > clocks, but I only have two in the code I've worked with (similarly it
> > > > seems to only want two resets, not 4) so I'll have to see if I can
> > > > figure out how to adapt that.
> > >
> > > Possible since commit fe8abf332b8f ("usb: dwc3: support clocks and
> > > resets for DWC3 core").
> >
> > Ok. It *seems* like I can get it working with the existing binding
> > then. There's a little funkiness with the core expecting three clocks
> > while I only have two (currently I'm duplicating the "bus_early" clk
> > for "suspend". Is there a preferred way to do this sort of hack?), and
> > I'm a little worried that only the first reset is being used (instead
> > of the 4 specified), but it seems to work so far.
>
> I would assume that you simply don't know how the 'suspend' clock is
> connected rather than you don't have one. But that's maybe not a
> problem you can fix.
>
> I would make dwc3 use devm_clk_bulk_get_all and allow for less than 3
> clocks. And do a similar change for resets.

So got a chance to start implementing this and it seems like it will
work. That said, it feels like I'm duplicating logic already in the
dwc-of-simple.c implementation (which already handles arbitrary clks
and resets), particularly if I try to implement the device specific
need_reset quirk used by HiKey960 (and rk3399).

Do you feel having that logic copied is worth avoiding the extra
bindings? Or is it too duplicative?

thanks
-john