linux-kernel - Re: [PATCH v2 1/3] dt-bindings: clock: qcom: Add SM8750 GPU clocks

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Message-ID: <7d444f4c-fa1f-4436-b93a-f2d2b6d49de2@oss.qualcomm.com>
Date: Thu, 24 Jul 2025 12:53:14 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Krzysztof Kozlowski <krzk@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>
Cc: Bjorn Andersson <andersson@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd
 <sboyd@...nel.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley
 <conor+dt@...nel.org>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] dt-bindings: clock: qcom: Add SM8750 GPU clocks

On 7/24/25 10:18 AM, Krzysztof Kozlowski wrote:
> On Wed, Jul 23, 2025 at 10:38:48PM +0200, Konrad Dybcio wrote:
>> From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
>>
>> The SM8750 features a "traditional" GPU_CC block, much of which is
>> controlled through the GMU microcontroller. Additionally, there's
>> an separate GX_CC block, where the GX GDSC is moved.
>>
>> Add bindings to accommodate for that.
>>
>> Signed-off-by: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
>> ---

[...]

>> +title: Qualcomm Graphics Clock & Reset Controller on SM8750
> 
> There is no clocks nor resets here. Only power domains.

There are clocks and resets in this IP block (inside the register
space mentioned in the dt patch/example), but the OS is not supposed
to poke at them (it can in theory, but we have a uC - the GMU -
doing the same thing so it would be stepping on one another's toes..).
Not sure how to express that.

I could for example add #define indices in include/dt-bindings, listing
out the clocks and never consume them. Does that sound fair?

> 
>> +
>> +maintainers:
>> +  - Konrad Dybcio <konradybcio@...nel.org>
>> +
>> +description: |
>> +  Qualcomm graphics clock control module provides the clocks, resets and power
> 
> Also confusing.
> 
>> +  domains on Qualcomm SoCs.
>> +
>> +  See also:
>> +    include/dt-bindings/reset/qcom,sm8750-gpucc.h
> 
> reset or clock path?

Ugh, clock

> 
>> +
>> +properties:
>> +  compatible:
>> +    enum:
>> +      - qcom,sm8750-gxcc
>> +
>> +  reg:
>> +    maxItems: 1
>> +
>> +  power-domains:
>> +    items:
>> +      - description: GFX voltage rail
>> +      - description: MX_COLLAPSIBLE voltage rail
>> +      - description: GPU_CC_CX GDSC
>> +
>> +  '#power-domain-cells':
>> +    const: 1
>> +
>> +required:
>> +  - compatible
>> +  - power-domains
>> +  - '#power-domain-cells'
>> +
> 
> You miss ref... or this is a bit confusing.
ref to what? qcom,gcc? I specifically omitted it, as that adds
requirements which you stated above.

Konrad

> 
>> +unevaluatedProperties: false
> 
> additionalProperties instead
> 
>> +
>> +examples:
>> +  - |
>> +    #include <dt-bindings/clock/qcom,sm8750-gpucc.h>
>> +    #include <dt-bindings/power/qcom,rpmhpd.h>
>> +
>> +    soc {
>> +        #address-cells = <2>;
>> +        #size-cells = <2>;
>> +
>> +        clock-controller@...4000 {
> 
> No, clock controllers have clock-cells. This cannot be a clock
> controller if it does not have any clocks for anyone to use.
> 
> Best regards,
> Krzysztof
>