linux-kernel - Re: [PATCH v2 2/3] dt-bindings: opp: Add v2-qcom-adreno vendor bindings

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Message-ID: <c5e868e1-2dae-466c-a6fc-ef0f247fa0ce@quicinc.com>
Date: Fri, 1 Nov 2024 21:54:56 +0530
From: Akhil P Oommen <quic_akhilpo@...cinc.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
CC: Krzysztof Kozlowski <krzk@...nel.org>, Rob Clark <robdclark@...il.com>,
        Sean Paul <sean@...rly.run>, Konrad Dybcio <konradybcio@...nel.org>,
        "Abhinav
 Kumar" <quic_abhinavk@...cinc.com>,
        Marijn Suijten
	<marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, "Simona
 Vetter" <simona@...ll.ch>,
        Viresh Kumar <vireshk@...nel.org>, Nishanth Menon
	<nm@...com>,
        Stephen Boyd <sboyd@...nel.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        <linux-arm-msm@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <freedreno@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
        <linux-pm@...r.kernel.org>, <devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 2/3] dt-bindings: opp: Add v2-qcom-adreno vendor
 bindings

On 10/25/2024 11:58 AM, Dmitry Baryshkov wrote:
> On Thu, Oct 24, 2024 at 12:56:58AM +0530, Akhil P Oommen wrote:
>> On 10/22/2024 11:19 AM, Krzysztof Kozlowski wrote:
>>> On Mon, Oct 21, 2024 at 05:23:43PM +0530, Akhil P Oommen wrote:
>>>> Add a new schema which extends opp-v2 to support a new vendor specific
>>>> property required for Adreno GPUs found in Qualcomm's SoCs. The new
>>>> property called "qcom,opp-acd-level" carries a u32 value recommended
>>>> for each opp needs to be shared to GMU during runtime.
>>>>
>>>> Cc: Rob Clark <robdclark@...il.com>
>>>> Signed-off-by: Akhil P Oommen <quic_akhilpo@...cinc.com>
>>>> ---
>>>>  .../bindings/opp/opp-v2-qcom-adreno.yaml           | 96 ++++++++++++++++++++++
>>>>  1 file changed, 96 insertions(+)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/opp/opp-v2-qcom-adreno.yaml b/Documentation/devicetree/bindings/opp/opp-v2-qcom-adreno.yaml
>>>> new file mode 100644
>>>> index 000000000000..6d50c0405ef8
>>>> --- /dev/null
>>>> +++ b/Documentation/devicetree/bindings/opp/opp-v2-qcom-adreno.yaml
>>>> @@ -0,0 +1,96 @@
>>>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>>>> +%YAML 1.2
>>>> +---
>>>> +$id: http://devicetree.org/schemas/opp/opp-v2-qcom-adreno.yaml#
>>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>>> +
>>>> +title: Qualcomm Adreno compatible OPP supply
>>>> +
>>>> +description:
>>>> +  Adreno GPUs present in Qualcomm's Snapdragon chipsets uses an OPP specific
>>>> +  ACD related information tailored for the specific chipset. This binding
>>>> +  provides the information needed to describe such a hardware value.
>>>> +
>>>> +maintainers:
>>>> +  - Rob Clark <robdclark@...il.com>
>>>> +
>>>> +allOf:
>>>> +  - $ref: opp-v2-base.yaml#
>>>> +
>>>> +properties:
>>>> +  compatible:
>>>> +    items:
>>>> +      - const: operating-points-v2-adreno
>>>> +      - const: operating-points-v2
>>>> +
>>>> +patternProperties:
>>>> +  '^opp-?[0-9]+$':
>>>
>>> '-' should not be optional. opp1 is not expected name.
>>
>> Agree. Will change this to '^opp-[0-9]+$'
>>
>>>
>>>> +    type: object
>>>> +    additionalProperties: false
>>>> +
>>>> +    properties:
>>>> +      opp-hz: true
>>>> +
>>>> +      opp-level: true
>>>> +
>>>> +      opp-peak-kBps: true
>>>> +
>>>> +      opp-supported-hw: true
>>>> +
>>>> +      qcom,opp-acd-level:
>>>> +        description: |
>>>> +          A positive value representing the ACD (Adaptive Clock Distribution,
>>>> +          a fancy name for clk throttling during voltage droop) level associated
>>>> +          with this OPP node. This value is shared to a co-processor inside GPU
>>>> +          (called Graphics Management Unit a.k.a GMU) during wake up. It may not
>>>> +          be present for some OPPs and GMU will disable ACD while transitioning
>>>> +          to that OPP. This value encodes a voltage threshold and few other knobs
>>>> +          which are identified by characterization of the SoC. So, it doesn't have
>>>> +          any unit.
>>>
>>> Thanks for explanation and other updates. I am still not happy with this
>>> property. I do not see reason why DT should encode magic values in a
>>> quite generic piece of code. This creates poor ABI, difficult to
>>> maintain or understand.
>>>
>>
>> Configuring GPU ACD block with its respective value is a requirement for each OPP.
>> So OPP node seems like the natural place for this data.
>>
>> If it helps to resolve your concerns, I can elaborate the documentation with
>> details on the GMU HFI interface where this value should be passed on to the
>> hardware. Also replace "few other knobs" with "Delay cycles & Calibration margin"
>> in the above doc.
> 
> Usually the preference for DT is to specify data in a sensible way
> rather than just the values being programmed to the register. Is it
> possible to implement this approach for ACD values?

I am still checking about this. Will get back.

-Akhil

> 
>>  
>>>
>