linux-kernel - Re: [PATCH v1 2/4] dt-bindings: clock: Add support for the MSM8998 mmcc

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Message-ID: <154940496255.169292.11279175475668034167@swboyd.mtv.corp.google.com>
Date:   Tue, 05 Feb 2019 14:16:02 -0800
From:   Stephen Boyd <sboyd@...nel.org>
To:     Jeffrey Hugo <jhugo@...eaurora.org>, bjorn.andersson@...aro.org,
        mark.rutland@....com, mturquette@...libre.com, robh+dt@...nel.org
Cc:     marc.w.gonzalez@...e.fr, andy.gross@...aro.org,
        david.brown@...aro.org, linux-arm-msm@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v1 2/4] dt-bindings: clock: Add support for the MSM8998 mmcc

Quoting Jeffrey Hugo (2019-02-05 14:08:43)
> On 2/5/2019 3:02 PM, Stephen Boyd wrote:
> > Quoting Jeffrey Hugo (2019-01-30 08:35:59)
> >> Document the multimedia clock controller found on MSM8998
> >>
> >> Signed-off-by: Jeffrey Hugo <jhugo@...eaurora.org>
> >> ---
> >>   Documentation/devicetree/bindings/clock/qcom,mmcc.txt | 7 +++++++
> >>   1 file changed, 7 insertions(+)
> >>
> >> diff --git a/Documentation/devicetree/bindings/clock/qcom,mmcc.txt b/Documentation/devicetree/bindings/clock/qcom,mmcc.txt
> >> index 8b0f784..ae85bca 100644
> >> --- a/Documentation/devicetree/bindings/clock/qcom,mmcc.txt
> >> +++ b/Documentation/devicetree/bindings/clock/qcom,mmcc.txt
> >> @@ -10,11 +10,18 @@ Required properties :
> >>                          "qcom,mmcc-msm8960"
> >>                          "qcom,mmcc-msm8974"
> >>                          "qcom,mmcc-msm8996"
> >> +                       "qcom,mmcc-msm8998"
> >>   
> >>   - reg : shall contain base register location and length
> >>   - #clock-cells : shall contain 1
> >>   - #reset-cells : shall contain 1
> >>   
> >> +For MSM8998 only:
> >> +       - clocks: a list of phandles and clock-specifier pairs,
> >> +                 one for each entry in clock-names.
> >> +       - clock-names: "xo" for the xo clock,
> >> +                      "gpll0" for the global pll 0 clock.
> > 
> > Wouldn't the DSI plls also be listed here? And anything else that is
> > external to this clock controller?
> > 
> 
> We can't get the DSI plls from DT as far as I am aware (upstream).  That 
> is why I mentioned in the cover letter we need to rely on the global 
> namespace.

Why not? Because the DSI PLL isn't a clk provider? Or it doesn't have
#clock-cells? Please try to use the DSI PLLs from DT or at least specify
them in the binding as optional clocks that may not matter if DSI is not
enabled for example.

> 
> Also, the DSI plls, etc present a chicken and egg situation, as the plls 
> require mmcc, and mmcc requires the plls.  I forsee an unsolvable 
> EPROBE_DEFER issue.
> 

We've "solved" that problem with orphan clks and the clk parent rewrite
series. Maybe you can try it out to help flush out any bugs lurking
there.