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

[Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>]

On 4.12.2024 7:18 PM, Akhil P Oommen wrote:
> On 11/16/2024 1:17 AM, Dmitry Baryshkov wrote:
>> On Fri, 15 Nov 2024 at 19:54, Akhil P Oommen <quic_akhilpo@quicinc.com> wrote:
>>>
>>> On 11/15/2024 3:54 AM, Dmitry Baryshkov wrote:
>>>> Hello Akhil,
>>>>
>>>> On Thu, 14 Nov 2024 at 20:50, Akhil P Oommen <quic_akhilpo@quicinc.com> wrote:
>>>>>
>>>>> On 11/1/2024 9:54 PM, Akhil P Oommen wrote:
>>>>>> 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@gmail.com>
>>>>>>>>>> Signed-off-by: Akhil P Oommen <quic_akhilpo@quicinc.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@gmail.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?
>>>>>
>>>>> Krzysztof/Dmitry,
>>>>>
>>>>> BIT(0)-BIT(15) are static configurations which doesn't change between
>>>>> OPPs. We can move it to driver.
>>>>>
>>>>> BIT(16)-BIT(31) indicates a threshold margin which triggers ACD. We can
>>>>> keep this in the devicetree. And the driver can construct the final
>>>>> value from both data and send it to GMU.
>>>>>
>>>>> If this is acceptable, I will send the v3 revision.
>>>>
>>>> Can the upper bitfield have a sensible representation in DT (like uV
>>>> or something similar)?
>>>
>>> Closest approximation is quantized voltage steps. So, unit-less.
>>> Converting it to the exact voltage requires identifying the pmic voltage
>>> steps and other stuffs which are outside of my expertise.
>>>
>>> It is convenient if we can abstract it as an integer which correlates
>>> with the voltage margin that should be maintained for each regulator corner.
> 
> Krzysztof,
> 
> Could you please confirm if this approach would be acceptable?
> 
> To reiterate, move the lower 16 bits which is same across OPPs to the
> driver. Abstract the higher 16 bits as number of quantized voltage
> margin when ACD mitigation gets triggered.

I know I'm not Krzysztof, but given this is ultimately a magic value
passed to the firmware, I'm a bit lukewarm on decomposing it and would
rather see the entire 32b passed in a property, so that if a future
target needs a different constant in the lower word, we don't have to
pull our hair out again, trying to add more spaghetti logic to account
for that.

Konrad