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

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Message-ID: <a048afe5-e87a-b539-1558-a26464622c1c@codeaurora.org>
Date:   Tue, 5 Feb 2019 15:36:26 -0700
From:   Jeffrey Hugo <jhugo@...eaurora.org>
To:     Stephen Boyd <sboyd@...nel.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

On 2/5/2019 3:16 PM, Stephen Boyd wrote:
> 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.

I had thought that there wasn't a DT node that exposed those (I find it 
very odd how the DSI PLLs get inited), but upon checking again, I see 
what I have missed.  I'll need to incorporate them now.

> 
>>
>> 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.
> 

Thanks for the reference in your other reply.  Will have a look.

-- 
Jeffrey Hugo
Qualcomm Datacenter Technologies as an affiliate of Qualcomm 
Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.