linux-kernel - Re: [PATCH 2/5] clk: qcom: apcs-msm8916: get parent clock names from DT

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Date:   Tue, 10 Sep 2019 11:40:34 +0200
From:   Jorge Ramirez <jorge.ramirez-ortiz@...aro.org>
To:     Stephen Boyd <sboyd@...nel.org>
Cc:     agross@...nel.org, mturquette@...libre.com,
        bjorn.andersson@...aro.org, niklas.cassel@...aro.org,
        linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] clk: qcom: apcs-msm8916: get parent clock names from
 DT

On 9/10/19 11:34, Jorge Ramirez wrote:
> On 9/10/19 11:14, Stephen Boyd wrote:
>> Quoting Jorge Ramirez-Ortiz, Linaro (2019-09-09 09:54:08)
>>> On 09/09/19 09:17:03, Stephen Boyd wrote:
>>>> But now the binding is different for the same compatible. I'd prefer we
>>>> keep using devm_clk_get() and use a device pointer here and reorder the
>>>> map and parent arrays instead. The clocks property shouldn't change in a
>>>> way that isn't "additive" so that we maintain backwards compatibility.
>>>>
>>>
>>> but the backwards compatibility is fully maintained - that is the main reason
>>> behind the change. the new stuff is that  instead of hardcoding the
>>> names in the source - like it is being done on the msm8916- we provide
>>> the clocks in the dts node (a cleaner approach with the obvious
>>> benefit of allowing new users to be added without having to modify the
>>> sources).
>>>
>>
>> This is not a backwards compatible change.
>>
>>>>> --- a/arch/arm64/boot/dts/qcom/msm8916.dtsi
>>>>> +++ b/arch/arm64/boot/dts/qcom/msm8916.dtsi
>>>>> @@ -429,7 +429,8 @@
>>>>>      compatible = "qcom,msm8916-apcs-kpss-global", "syscon";
>>>>>      reg = <0xb011000 0x1000>;
>>>>>      #mbox-cells = <1>;
>>>>> -                   clocks = <&a53pll>;
>>>>> +                 clocks = <&gcc GPLL0_VOTE>, <&a53pll>;
>>>>> +                 clock-names = "aux", "pll";
>>>>>                       #clock-cells = <0>;
>>>>>                };
>>>>>                                                                                                                 
>>
>> Because the "clocks" property changed from
>>
>> 	<&a53pll>
>>
>> to
>>
>> 	<&gcc GPLL0_VOTE>, <&a53pll>
>>
>> and that moves pll to cell 1 instead of cell 0.
>>
>>
> 
> what do you mean by backwards compatible? because this change does not
> break previous clients.

as per the comments I added to the code (in case this helps framing the
discussion)

[..]
legacy bindings only defined the pll parent clock (index = 0) with no
name; when both of the parents are specified in the bindings, the
pll is the second one (index = 1).
[..]



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