linux-kernel - Re: [PATCH v6 5/6] arm64: dts: qcom: sm8450: Add opp table support to PCIe

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Message-ID: <f3f3329b-0dc9-4652-9f23-d55852f046d8@quicinc.com>
Date: Mon, 19 Feb 2024 12:32:52 +0530
From: Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
To: Konrad Dybcio <konrad.dybcio@...aro.org>,
        Viresh Kumar
	<viresh.kumar@...aro.org>
CC: Manivannan Sadhasivam <mani@...nel.org>,
        Bjorn Andersson
	<andersson@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Lorenzo
 Pieralisi" <lpieralisi@...nel.org>,
        Krzysztof Wilczyński
	<kw@...ux.com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski
	<krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        "Rob
 Herring" <robh+dt@...nel.org>,
        Johan Hovold <johan+linaro@...nel.org>,
        "Brian
 Masney" <bmasney@...hat.com>,
        Georgi Djakov <djakov@...nel.org>, <linux-arm-msm@...r.kernel.org>,
        <vireshk@...nel.org>, <quic_vbadigan@...cinc.com>,
        <quic_skananth@...cinc.com>, <quic_nitegupt@...cinc.com>,
        <linux-pci@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 5/6] arm64: dts: qcom: sm8450: Add opp table support to
 PCIe



On 2/10/2024 2:44 AM, Konrad Dybcio wrote:
> On 2.02.2024 08:33, Viresh Kumar wrote:
>> On 01-02-24, 15:45, Konrad Dybcio wrote:
>>> I'm lukewarm on this.
>>>
>>> A *lot* of hardware has more complex requirements than "x MBps at y MHz",
>>> especially when performance counters come into the picture for dynamic
>>> bw management.
>>>
>>> OPP tables can't really handle this properly.
>>
>> There was a similar concern for voltages earlier on and we added the capability
>> of adjusting the voltage for OPPs in the OPP core. Maybe something similar can
>> be done here ?
>>
> I really don't think it's fitting.. At any moment the device may require any
> bandwidth value between 0 and MAX_BW_PER_LINK_GEN * LINK_WIDTH..
> 
> Konrad
Viresh & konrad can you both come to conclusion on this.

- Krishna Chaitanya.