linux-kernel - Re: [PATCH v8 7/7] PCI: qcom: Add OPP support to scale performance state of power domain

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Message-ID: <20240405082306.GD2953@thinkpad>
Date: Fri, 5 Apr 2024 13:53:06 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
Cc: Manivannan Sadhasivam <mani@...nel.org>,
	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>,
	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 v8 7/7] PCI: qcom: Add OPP support to scale performance
 state of power domain

On Tue, Mar 05, 2024 at 04:44:20PM +0530, Krishna Chaitanya Chundru wrote:
> 
> 
> On 3/4/2024 11:35 PM, Manivannan Sadhasivam wrote:
> > On Sat, Mar 02, 2024 at 09:30:01AM +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.
> > > 
> > > PCIe controller can operate on different RPMh performance state of power
> > > domain based on the speed of the link. And this performance state varies
> > > from target to target, like some controllers support GEN3 in NOM (Nominal)
> > > voltage corner, while some other supports GEN3 in low SVS (static voltage
> > > scaling).
> > > 
> > > The SoC can be more power efficient if we scale the performance state
> > > based on the aggregate PCIe link bandwidth.
> > > 
> > > Add Operating Performance Points (OPP) support to vote for RPMh state based
> > > on the aggregate link bandwidth.
> > > 
> > > OPP can handle ICC bw voting also, so move ICC bw voting through OPP
> > > framework if OPP entries are present.
> > > 
> > > 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.
> > > 
> > > As we are moving ICC voting as part of OPP, don't initialize ICC if OPP
> > > is supported.
> > > 
> > > Signed-off-by: Krishna chaitanya chundru <quic_krichai@...cinc.com>
> > > ---
> > >   drivers/pci/controller/dwc/pcie-qcom.c | 81 +++++++++++++++++++++++++++-------
> > >   1 file changed, 66 insertions(+), 15 deletions(-)
> > > 
> > > diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> > > index a0266bfe71f1..2ec14bfafcfc 100644
> > > --- a/drivers/pci/controller/dwc/pcie-qcom.c
> > > +++ b/drivers/pci/controller/dwc/pcie-qcom.c

[...]

> > >   static int qcom_pcie_link_transition_count(struct seq_file *s, void *data)
> > > @@ -1472,8 +1491,10 @@ static void qcom_pcie_init_debugfs(struct qcom_pcie *pcie)
> > >   static int qcom_pcie_probe(struct platform_device *pdev)
> > >   {
> > >   	const struct qcom_pcie_cfg *pcie_cfg;
> > > +	unsigned long max_freq = INT_MAX;
> > >   	struct device *dev = &pdev->dev;
> > >   	struct qcom_pcie *pcie;
> > > +	struct dev_pm_opp *opp;
> > >   	struct dw_pcie_rp *pp;
> > >   	struct resource *res;
> > >   	struct dw_pcie *pci;
> > > @@ -1540,9 +1561,36 @@ static int qcom_pcie_probe(struct platform_device *pdev)
> > >   		goto err_pm_runtime_put;
> > >   	}
> > > -	ret = qcom_pcie_icc_init(pcie);
> > > -	if (ret)
> > > +	 /* OPP table is optional */
> > > +	ret = devm_pm_opp_of_add_table(dev);
> > > +	if (ret && ret != -ENODEV) {
> > > +		dev_err_probe(dev, ret, "Failed to add OPP table\n");
> > >   		goto err_pm_runtime_put;
> > > +	}
> > > +
> > > +	/*
> > > +	 * Use highest OPP here if the OPP table is present. At the end of
> > 
> > Why highest opp? For ICC, we set minimal bandwidth before.
> > 
> In OPP we are voting for both ICC and voltage corner also, if we didn't vote
> for maximum voltage core the PCIe link may not come in maximum supported
> speed. Due to that we are voting for Maximum value.
> 

Okay, then this information should be part of the comment.

- Mani

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