linux-kernel - Re: [PATCH v7 7/7] PCI: qcom: Add OPP support to scale performance state of power domain

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Message-ID: <c9369d12-c31c-50cd-7b2c-974839388d72@quicinc.com>
Date: Wed, 28 Feb 2024 12:18:06 +0530
From: Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
To: Bjorn Helgaas <helgaas@...nel.org>
CC: Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio
	<konrad.dybcio@...aro.org>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Rob Herring
	<robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
        Krzysztof Kozlowski
	<krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.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>, <linux-pci@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <vireshk@...nel.org>, <quic_vbadigan@...cinc.com>,
        <quic_skananth@...cinc.com>, <quic_nitegupt@...cinc.com>,
        <quic_parass@...cinc.com>
Subject: Re: [PATCH v7 7/7] PCI: qcom: Add OPP support to scale performance
 state of power domain



On 2/28/2024 5:15 AM, Bjorn Helgaas wrote:
> On Tue, Feb 27, 2024 at 05:36:38PM -0600, Bjorn Helgaas wrote:
>> On Fri, Feb 23, 2024 at 08:18:04PM +0530, Krishna chaitanya chundru wrote:
>>> QCOM Resource Power Manager-hardened (RPMh) is a hardware block which
>>> maintains hardware state of a regulator by performing max aggregation of
>>> the requests made by all of the clients.
> 
>>> It is manadate to scale the performance state based up on the PCIe speed
>>> link operates so that SoC can run under optimum power conditions.
>>
>> It sounds like it's more power efficient, but not actually
>> *mandatory*.  Maybe something like this?
>>
>>    The SoC can be more power efficient if we scale the performance
>>    state based on the aggregate PCIe link speed.
> 
> Actually, maybe it would be better to say "aggregate PCIe link
> bandwidth", because we use "speed" elsewhere (PCIE_SPEED2MBS_ENC(),
> etc) to refer specifically to the data rate independent of the width.
> 
>>> Add Operating Performance Points(OPP) support to vote for RPMh state based
>>> upon the speed link is operating.
>>
>> "... based on the link speed."
> 
> "... based on the aggregate link bandwidth."
> 
>>> In PCIe certain speeds like GEN1x2 & GEN2x1 or GEN3x2 & GEN4x1 use
>>> same bw and frequency and thus the OPP entry, so use frequency based
>>> search to reduce number of entries in the OPP table.
>>
>> GEN1x2, GEN2x1, etc are not "speeds".  I would say:
>>
>>    Different link configurations may share the same aggregate speed,
>>    e.g., a 2.5 GT/s x2 link and a 5.0 GT/s x1 link have the same speed
>>    and share the same OPP entry.
> 
>    Different link configurations may share the same aggregate
>    bandwidth, e.g., a 2.5 GT/s x2 link and a 5.0 GT/s x1 link
>    have the same bandwidth and share the same OPP entry.
- I will update the commit message as suggested in my next series.

- Krishna Chaitanya.