linux-kernel - Re: [PATCH v2 2/4] dt-bindings: arm: mediatek: Add new bindings of MediaTek frequency hopping

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Message-ID: <551a0a6d-107e-d521-57cd-90c428576d69@collabora.com>
Date:   Thu, 15 Sep 2022 08:56:25 +0200
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Johnson Wang <johnson.wang@...iatek.com>, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, sboyd@...nel.org
Cc:     linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        Project_Global_Chrome_Upstream_Group@...iatek.com,
        Edward-JW Yang <edward-jw.yang@...iatek.com>
Subject: Re: [PATCH v2 2/4] dt-bindings: arm: mediatek: Add new bindings of
 MediaTek frequency hopping

Il 15/09/22 06:00, Johnson Wang ha scritto:
> Hi Angelo,
> 
> Thanks for your review.
> 
> On Wed, 2022-09-14 at 15:46 +0200, AngeloGioacchino Del Regno wrote:
>> Il 14/09/22 14:45, Johnson Wang ha scritto:
>>> Add the new binding documentation for MediaTek frequency hopping
>>> and spread spectrum clocking control.
>>>
>>> Co-developed-by: Edward-JW Yang <edward-jw.yang@...iatek.com>
>>> Signed-off-by: Edward-JW Yang <edward-jw.yang@...iatek.com>
>>> Signed-off-by: Johnson Wang <johnson.wang@...iatek.com>
>>> ---
>>>    .../bindings/arm/mediatek/mediatek,fhctl.yaml | 47
>>> +++++++++++++++++++
>>>    1 file changed, 47 insertions(+)
>>>    create mode 100644
>>> Documentation/devicetree/bindings/arm/mediatek/mediatek,fhctl.yaml
>>>
>>> diff --git
>>> a/Documentation/devicetree/bindings/arm/mediatek/mediatek,fhctl.yam
>>> l
>>> b/Documentation/devicetree/bindings/arm/mediatek/mediatek,fhctl.yam
>>> l
>>> new file mode 100644
>>> index 000000000000..7b0fd0889bb6
>>> --- /dev/null
>>> +++
>>> b/Documentation/devicetree/bindings/arm/mediatek/mediatek,fhctl.yam
>>> l
>>> @@ -0,0 +1,47 @@
>>> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
>>> +%YAML 1.2
>>> +---
>>> +$id:
>>> https://urldefense.com/v3/__http://devicetree.org/schemas/arm/mediatek/mediatek,fhctl.yaml*__;Iw!!CTRNKA9wMg0ARbw!3sumdhtrK5Ah5_rfIilgm4UUmnwkkqMpc3r_ZfkLfsXsLn-_AKm9ZokhJGD1Fl-gJpckAKHZh-jNVW64KRU8Duv1kg$
>>>   
>>> +$schema:
>>> https://urldefense.com/v3/__http://devicetree.org/meta-schemas/core.yaml*__;Iw!!CTRNKA9wMg0ARbw!3sumdhtrK5Ah5_rfIilgm4UUmnwkkqMpc3r_ZfkLfsXsLn-_AKm9ZokhJGD1Fl-gJpckAKHZh-jNVW64KRWMb8jIsw$
>>>   
>>> +
>>> +title: MediaTek frequency hopping and spread spectrum clocking
>>> control
>>> +
>>> +maintainers:
>>> +  - Edward-JW Yang <edward-jw.yang@...iatek.com>
>>> +
>>> +description: |
>>> +  Frequency hopping control (FHCTL) is a piece of hardware that
>>> control
>>> +  some PLLs to adopt "hopping" mechanism to adjust their
>>> frequency.
>>> +  Spread spectrum clocking (SSC) is another function provided by
>>> this hardware.
>>> +
>>> +properties:
>>> +  compatible:
>>> +    const: mediatek,mt8186-fhctl
>>> +
>>> +  reg:
>>> +    maxItems: 1
>>
>> There are still a few issues in this binding that I can immediately
>> see...
>>
>>> +
>>> +  clocks:
>>
>> MT8195 has 23 PLLs, MT8186 has 14, but perhaps in the future we may
>> see
>> something more than that on some newer SoC, so...
>>
>>     clocks:
>>       maxItems: 30
> 
> May I add "minItems: 1" to clocks property?
> 

Of course you can! Sorry for the incomplete advice here :-)

> Without this, dt_binding_check will fail because we don't have enough
> clocks in the example. (Both MT8195 and MT8186 don't have 30 PLLs)
> 
>>
>>> +    description: Phandles of the PLL with FHCTL hardware
>>> capability.
>>> +
>>> +  mediatek,hopping-ssc-percents:
>>> +    description: The percentage of spread spectrum clocking for
>>> one PLL.
>>> +    $ref: /schemas/types.yaml#/definitions/uint32
>>
>> This is an array, so...
>> $ref: /schemas/types.yaml#/definitions/uint32-array
>>
>> ...also, maxItems?
> 
> As you know, mediatek,hopping-ssc-percents property is used to specify
> ssc rate for matching clocks.
> 
> If we have to add maxItems, I think we should specify the same value
> as clocks property. Is my understanding wrong?
> 

Your understanding is right. The number of min/max items on the ssc
percents will be the same as clocks.

Regards,
Angelo

> 
> Thanks!
> 
> BRs,
> Johnson Wang
>>
>> and you should also specify:
>>
>> default: 0   <- because, by default, SSC is disabled
>> minimum: 0   <- because this is the minimum accepted value
>>
>>
>> Regards,
>> Angelo
>>
>>> +    maximum: 8
>>> +
>>> +required:
>>> +  - compatible
>>> +  - reg
>>> +  - clocks
>>> +
>>> +additionalProperties: false
>>> +
>>> +examples:
>>> +  - |
>>> +    #include <dt-bindings/clock/mt8186-clk.h>
>>> +    fhctl: fhctl@...0ce00 {
>>> +        compatible = "mediatek,mt8186-fhctl";
>>> +        reg = <0x1000c000 0xe00>;
>>> +        clocks = <&apmixedsys CLK_APMIXED_MSDCPLL>;
>>> +        mediatek,hopping-ssc-percents = <3>;
>>> +    };
>>
>>
> 

-- 
AngeloGioacchino Del Regno
Software Engineer

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