linux-kernel - Re: [PATCH 0/3] opp: Add bw_factor support to adjust bandwidth dynamically

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Message-ID: <7f1393ab-5ae2-428a-92f8-3c8a5df02058@oss.qualcomm.com>
Date: Fri, 1 Aug 2025 15:05:31 +0530
From: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
To: Viresh Kumar <viresh.kumar@...aro.org>
Cc: Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kwilczynski@...nel.org>,
        Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley
 <conor+dt@...nel.org>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH 0/3] opp: Add bw_factor support to adjust bandwidth
 dynamically



On 8/1/2025 2:26 PM, Viresh Kumar wrote:
> On 01-08-25, 13:58, Krishna Chaitanya Chundru wrote:
>> When ever PCIe link speed/width changes we need to update the OPP votes,
>> If we use named properties approach we might not be able to change it
>> dynamically without removing the OPP table first. For that reason only
>> we haven't used that approach.
> 
> I am not sure I understand it fully. I thought this was a one time configuration
> you were required to do at boot time based on platform's configuration.
>
I am not fully familiar with OPP here.

> If you need to change the performance at runtime, won't you switch to a
> different OPP ?
> 
yes we do set different OPP when we change it.

Currently we are fetching the OPP based on the frequency and setting
that OPP using dev_pm_opp_set_opp().

As you are suggesting to use dev_pm_opp_set_prop_name() here.
This what I understood

First set prop name using dev_pm_opp_set_prop_name then
set opp dev_pm_opp_set_opp()

if you want to change above one we need to first clear using
dev_pm_opp_put_prop_name() then again call dev_pm_opp_set_prop_name
& dev_pm_opp_set_opp()

I was in a impression that once you call dev_pm_opp_put_prop_name()
the previous votes will be removed. we don't want that to happen.
if this is not correct we can use this approach.

If this is not correct assumption can you point me any reference to this
I was not able to find any reference on this.

- Krishna Chaitanya.

> I don't have much knowledge of how PCIe works, maybe that's why the confusion.
>