linux-kernel - Re: [PATCH 1/7] dt-bindings: PCI: qcom: Add IPQ9574 specific compatible

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Message-ID: <dd48782f-e5ff-2bbe-93d0-cfdd491d5292@quicinc.com>
Date:   Wed, 8 Mar 2023 14:19:58 +0530
From:   Devi Priya <quic_devipriy@...cinc.com>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
CC:     Manivannan Sadhasivam <mani@...nel.org>, <agross@...nel.org>,
        <andersson@...nel.org>, <konrad.dybcio@...aro.org>,
        <lpieralisi@...nel.org>, <kw@...ux.com>, <robh@...nel.org>,
        <bhelgaas@...gle.com>, <krzysztof.kozlowski+dt@...aro.org>,
        <vkoul@...nel.org>, <kishon@...nel.org>, <mturquette@...libre.com>,
        <sboyd@...nel.org>, <p.zabel@...gutronix.de>,
        <linux-arm-msm@...r.kernel.org>, <linux-pci@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-phy@...ts.infradead.org>, <linux-clk@...r.kernel.org>,
        <quic_srichara@...cinc.com>, <quic_gokulsri@...cinc.com>,
        <quic_sjaganat@...cinc.com>, <quic_kathirav@...cinc.com>,
        <quic_arajkuma@...cinc.com>, <quic_anusha@...cinc.com>
Subject: Re: [PATCH 1/7] dt-bindings: PCI: qcom: Add IPQ9574 specific
 compatible



On 3/7/2023 8:26 PM, Dmitry Baryshkov wrote:
> On Tue, 7 Mar 2023 at 16:40, Devi Priya <quic_devipriy@...cinc.com> wrote:
>>
>>
>>
>> On 3/7/2023 6:26 PM, Manivannan Sadhasivam wrote:
>>> On Tue, Mar 07, 2023 at 03:15:08PM +0530, Devi Priya wrote:
>>>>
>>>>
>>>> On 3/3/2023 11:10 PM, Manivannan Sadhasivam wrote:
>>>>> On Fri, Mar 03, 2023 at 05:16:58PM +0200, Dmitry Baryshkov wrote:
>>>>>> 28 февраля 2023 г. 08:33:58 GMT+02:00, Manivannan Sadhasivam <mani@...nel.org> пишет:
>>>>>>> On Tue, Feb 28, 2023 at 10:56:53AM +0530, Devi Priya wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>> On 2/24/2023 1:53 PM, Manivannan Sadhasivam wrote:
>>>>>>>>> On Tue, Feb 14, 2023 at 10:11:29PM +0530, Devi Priya wrote:
>>>>>>>>>> Document the compatible for IPQ9574
>>>>>>>>>>
>>>>>>>> Hi Mani, Thanks for taking time to review the patch.
>>>>>>>>>
>>>>>>>>> You didn't mention about the "msi-parent" property that is being added
>>>>>>>>> by this patch
>>>>>>>> Sure, will update the commit message in the next spin
>>>>>>>>>
>>>>>>>>>> Signed-off-by: Devi Priya <quic_devipriy@...cinc.com>
>>>>>>>>>> ---
>>>>>>>>>>      .../devicetree/bindings/pci/qcom,pcie.yaml    | 72 ++++++++++++++++++-
>>>>>>>>>>      1 file changed, 70 insertions(+), 2 deletions(-)
>>>>>>>>>>
>>>>>>>>>> diff --git a/Documentation/devicetree/bindings/pci/qcom,pcie.yaml b/Documentation/devicetree/bindings/pci/qcom,pcie.yaml
>>>>>>>>>> index 872817d6d2bd..dabdf2684e2d 100644
>>>>>>>>>> --- a/Documentation/devicetree/bindings/pci/qcom,pcie.yaml
>>>>>>>>>> +++ b/Documentation/devicetree/bindings/pci/qcom,pcie.yaml
>>>>>>>>>> @@ -26,6 +26,7 @@ properties:
>>>>>>>>>>                - qcom,pcie-ipq8064-v2
>>>>>>>>>>                - qcom,pcie-ipq8074
>>>>>>>>>>                - qcom,pcie-ipq8074-gen3
>>>>>>>>>> +          - qcom,pcie-ipq9574
>>>>>>>>>>                - qcom,pcie-msm8996
>>>>>>>>>>                - qcom,pcie-qcs404
>>>>>>>>>>                - qcom,pcie-sa8540p
>>>>>>>>>> @@ -44,11 +45,11 @@ properties:
>>>>>>>>>>        reg:
>>>>>>>>>>          minItems: 4
>>>>>>>>>> -    maxItems: 5
>>>>>>>>>> +    maxItems: 6
>>>>>>>>>>        reg-names:
>>>>>>>>>>          minItems: 4
>>>>>>>>>> -    maxItems: 5
>>>>>>>>>> +    maxItems: 6
>>>>>>>>>>        interrupts:
>>>>>>>>>>          minItems: 1
>>>>>>>>>> @@ -105,6 +106,8 @@ properties:
>>>>>>>>>>          items:
>>>>>>>>>>            - const: pciephy
>>>>>>>>>> +  msi-parent: true
>>>>>>>>>> +
>>>>>>>>>>        power-domains:
>>>>>>>>>>          maxItems: 1
>>>>>>>>>> @@ -173,6 +176,27 @@ allOf:
>>>>>>>>>>                  - const: parf # Qualcomm specific registers
>>>>>>>>>>                  - const: config # PCIe configuration space
>>>>>>>>>> +  - if:
>>>>>>>>>> +      properties:
>>>>>>>>>> +        compatible:
>>>>>>>>>> +          contains:
>>>>>>>>>> +            enum:
>>>>>>>>>> +              - qcom,pcie-ipq9574
>>>>>>>>>> +    then:
>>>>>>>>>> +      properties:
>>>>>>>>>> +        reg:
>>>>>>>>>> +          minItems: 5
>>>>>>>>>> +          maxItems: 6
>>>>>>>>>> +        reg-names:
>>>>>>>>>> +          minItems: 5
>>>>>>>>>> +          items:
>>>>>>>>>> +            - const: dbi # DesignWare PCIe registers
>>>>>>>>>> +            - const: elbi # External local bus interface registers
>>>>>>>>>> +            - const: atu # ATU address space
>>>>>>>>>> +            - const: parf # Qualcomm specific registers
>>>>>>>>>> +            - const: config # PCIe configuration space
>>>>>>>>>> +            - const: aggr_noc #PCIe aggr_noc
>>>>>>>>>
>>>>>>>>> Why do you need this region unlike other SoCs? Is the driver making use of it?
>>>>>>>> We have the aggr_noc region in ipq9574 to achieve higher throughput & to
>>>>>>>> handle multiple PCIe instances. The driver uses it to rate adapt 1-lane PCIe
>>>>>>>> clocks. My bad, missed it. Will add the driver changes in V2.
>>>>>>>
>>>>>>> Hmm, this is something new. How can you achieve higher throughput with this
>>>>>>> region? Can you explain more on how it is used?
>>>>>>
>>>>>> Based on the name of the region, it looks like it is an interconnect region.
>>>>>>
>>>>>
>>>>> Well, we only have BCM based interconnects so far. That's why I was curious
>>>>> about this region and its purpose.
>>>> For connected PCIe slave devices that are running at frequency lesser
>>>> than the ANOC frequency (342MHz), the rate adapter of ANOC needs to be
>>>> configured
>>>>>
>>>>>> Devi, if this is the case, then you have to handle it through the interconnect driver, rather than poking directly into these registers.
>>>>>
>>>>> If that so, it doesn't need to be added in this series itself. I believe that
>>>>> without aggr_noc region, the PCIe controller can still function properly with
>>>>> reduced performance. But you can add the interconnect support later as a
>>>>> separate series.
>>>> Sure, okay. The ANOC runs at a fixed frequency of 342MHz and the
>>>> interconnect clocks are not scaled. The aggr_noc register is just a magic
>>>> register for configuring it's rate adapter to ensure no wait cycles are
>>>> inserted.
>>>>
>>>
>>> If the purpose of the aggr_noc region is to configure the interconnect clock,
>>> then it should be modeled as an interconnect driver.
>> Can we use 'syscon' here, as we are not scaling the interconnect
>> frequency and this is just a single register write for setting
>> the rate adapter?
> 
> It should be done outside of the PCIe driver.
> It is not "just a single register". It is also setting the anoc/snoc
> clocks for USB. And maybe something else, which we haven't seen at
> this moment. You are still setting up the NoC, even if the icc
> frequency is not scaled.
> 
Sure Dmitry, Got it

Regards,
Devi Priya