Re: [PATCH] arm64: dts: mt8173: add clock_null

[Daniel Kurtz]

On Tue, Jul 7, 2015 at 9:07 PM, Sascha Hauer <s.hauer@xxxxxxxxxxxxxx> wrote:
> On Thu, Jun 18, 2015 at 01:29:11PM +0800, Eddie Huang wrote:
>> Add clk_null, which represents clocks that can not / need not
>> controlled by software.
>> There are many clocks' parent set to clk_null.
>>
>> Signed-off-by: James Liao <jamesjj.liao@xxxxxxxxxxxx>
>> Signed-off-by: Eddie Huang <eddie.huang@xxxxxxxxxxxx>
>> ---
>> Base on 4.1-rc1
>>
>> Change-Id: I4db9b40d07e28f54f7bae9b676316cbd6a962124
>> ---
>>  arch/arm64/boot/dts/mediatek/mt8173.dtsi | 6 ++++++
>>  1 file changed, 6 insertions(+)
>>
>> diff --git a/arch/arm64/boot/dts/mediatek/mt8173.dtsi b/arch/arm64/boot/dts/mediatek/mt8173.dtsi
>> index 924fdb6..4798f44 100644
>> --- a/arch/arm64/boot/dts/mediatek/mt8173.dtsi
>> +++ b/arch/arm64/boot/dts/mediatek/mt8173.dtsi
>> @@ -81,6 +81,12 @@
>>               cpu_on        = <0x84000003>;
>>       };
>>
>> +     clk_null: clk_null {
>> +             compatible = "fixed-clock";
>> +             clock-frequency = <0>;
>> +             #clock-cells = <0>;
>> +     };
>
> The discussion around this patch shows that we don't want to have this
> clock in the device tree as it is not a hardware description.
>
> Ok, fine. Eddie, you told us that the rate of the current clk_null children
> is not interesting. What's the motivation to send this patch anyway
> then? Why can't you keep its children on the orphan list where they are
> already now?
>
> Another possibility would be to instantiate the clk_null clock from C
> code rather than from the device tree. This way we wouldn't put any
> wrong descriptions into the device tree and still can implement the
> support for the real parent clocks when we actually need them.

Some device nodes, like mmc, use a clk_null phandle as one of their clocks:

mmc1: mmc@11240000 {
        compatible = "mediatek,mt8173-mmc",
                     "mediatek,mt8135-mmc";
        reg = <0 0x11240000 0 0x1000>;
        interrupts = <GIC_SPI 72 IRQ_TYPE_LEVEL_LOW>;
        clocks = <&pericfg CLK_PERI_MSDC30_1>,
                 <&clk_null>;
        clock-names = "source", "hclk";
        status = "disabled";
};

-Dan


> Sascha
>
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