linux-kernel - Re: [PATCH v6 6/6] PCI: qcom: Add OPP support to scale performance state of power domain

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Date: Thu, 1 Feb 2024 13:58:58 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Manivannan Sadhasivam <mani@...nel.org>
Cc: Krishna Chaitanya Chundru <quic_krichai@...cinc.com>, Bjorn Andersson <andersson@...nel.org>, 
	Konrad Dybcio <konrad.dybcio@...aro.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 6/6] PCI: qcom: Add OPP support to scale performance
 state of power domain

On Thu, 1 Feb 2024 at 13:54, Manivannan Sadhasivam <mani@...nel.org> wrote:
>
> On Tue, Jan 16, 2024 at 11:55:17AM +0200, Dmitry Baryshkov wrote:
> > On Tue, 16 Jan 2024 at 07:17, Krishna Chaitanya Chundru
> > <quic_krichai@...cinc.com> wrote:
> > >
> > >
> > >
> > > On 1/12/2024 9:03 PM, Dmitry Baryshkov wrote:
> > > > On Fri, 12 Jan 2024 at 16:25, Krishna chaitanya chundru
> > > > <quic_krichai@...cinc.com> 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 processors.
> > > >>
> > > >> PCIe controller can operate on different RPMh performance state of power
> > > >> domain based up on the speed of the link. And this performance state varies
> > > >> from target to target.
> > > >>
> > > >> 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.
> > > >>
> > > >> Add Operating Performance Points(OPP) support to vote for RPMh state based
> > > >> upon GEN speed link is operating.
> > > >>
> > > >> OPP can handle ICC bw voting also, so move icc bw voting through opp
> > > >> framework if opp entries are present.
> > > >>
> > > >> In PCIe certain gen speeds like GEN1x2 & GEN2X1 or GEN3x2 & GEN4x1 use
> > > >> same icc bw and has frequency, so use frequency based search to reduce
> > > >> number of entries in the opp table.
> > > >>
> > > >> 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 | 83 ++++++++++++++++++++++++++++------
> > > >>   1 file changed, 70 insertions(+), 13 deletions(-)
> > > >>
> > > >> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> > > >> index 035953f0b6d8..31512dc9d6ff 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)
> > > >> @@ -1471,8 +1502,10 @@ 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;
> > > >> @@ -1539,9 +1572,33 @@ 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;
> > > >> +       }
> > > >
> > > > Can we initialise the table from the driver if it is not found? This
> > > > will help us by having the common code later on.
> > > >
> > > we already icc voting if there is no opp table present in the dts.
> >
> > Yes. So later we have two different code paths: one for the OPP table
> > being present and another one for the absent OPP table. My suggestion
> > is to initialise minimal OPP table by hand and then have a common code
> > path in qcom_pcie_icc_update().
> >
>
> Are you suggesting to duplicate DT in the driver?

As a fallback for the cases when there is no OPP table in the driver
it might make sense. See
Otherwise the DT is still somewhat duplicated in the form of calling
icc functions directly.

-- 
With best wishes
Dmitry