linux-kernel - Re: [PATCH 1/2] dt-bindings: msm/dsi: Add ref clock for 10nm PHY

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Date:   Wed, 14 Nov 2018 15:32:36 -0800
From:   Stephen Boyd <swboyd@...omium.org>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     David Airlie <airlied@...ux.ie>,
        Mark Rutland <mark.rutland@....com>,
        Rob Clark <robdclark@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Archit Taneja <architt@...eaurora.org>,
        Sean Paul <seanpaul@...omium.org>,
        Rajesh Yadav <ryadav@...eaurora.org>,
        Douglas Anderson <dianders@...omium.org>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] dt-bindings: msm/dsi: Add ref clock for 10nm PHY

Quoting Matthias Kaehlcke (2018-11-14 14:42:52)
> On Tue, Nov 06, 2018 at 03:09:40PM -0800, Stephen Boyd wrote:
> > Quoting Matthias Kaehlcke (2018-11-02 14:45:33)
> > > Allow the 10nm PHY driver to get the ref clock from the DT.
> > > 
> > > Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
> > > ---
> > >  Documentation/devicetree/bindings/display/msm/dsi.txt | 4 ++++
> > >  1 file changed, 4 insertions(+)
> > > 
> > > diff --git a/Documentation/devicetree/bindings/display/msm/dsi.txt b/Documentation/devicetree/bindings/display/msm/dsi.txt
> > > index dfc743219bd88..d0d2046ceff69 100644
> > > --- a/Documentation/devicetree/bindings/display/msm/dsi.txt
> > > +++ b/Documentation/devicetree/bindings/display/msm/dsi.txt
> > > @@ -105,6 +105,10 @@ Required properties:
> > >  - power-domains: Should be <&mmcc MDSS_GDSC>.
> > >  - clocks: Phandles to device clocks. See [1] for details on clock bindings.
> > >  - clock-names: the following clocks are required:
> > > +  For 10nm PHY:
> > > +  * "iface"
> > > +  * "ref"
> > > +  For other PHYs:
> > >    * "iface"
> > 
> > Any reason we can't go back and do this for other phys too? They're all
> > the same with regards to this reference clk input.
> 
> To avoid breaking existing users, at least the 28nm PHY is used by
> msm8916. Also I don't have the hardware to test changes for other
> PHYs.
> 

Hmmm I don't see why we need to worry about breaking "legacy" users. If
they're using an undocumented but still working method of doing
something that should be OK, but I'd like to see us update the DTS and
binding to be more forward looking so that future designs don't carry
forward badness. And not having hardware hasn't really been a problem in
the past either. We can probably have someone from Linaro test on any
affected platforms.