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

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Date: Mon, 19 Feb 2024 15:58:34 +0530
From: Viresh Kumar <viresh.kumar@...aro.org>
To: Konrad Dybcio <konrad.dybcio@...aro.org>
Cc: Manivannan Sadhasivam <mani@...nel.org>,
	Krishna chaitanya chundru <quic_krichai@...cinc.com>,
	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 09-02-24, 22:14, 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..

Okay, I leave it up to you guys to decide on how you want to do it. I still
believe getting the information via DT is the right thing, but maybe I still
don't understand the problem fully.

Thanks.

-- 
viresh