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Date:   Mon, 9 Jan 2023 22:41:59 +0000
From:   Matthias Kaehlcke <mka@chromium.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Cc:     Dhruva Gole <d-gole@ti.com>, lpieralisi@kernel.org,
        robh@kernel.org, andersson@kernel.org, konrad.dybcio@linaro.org,
        kw@linux.com, bhelgaas@google.com, linux-pci@vger.kernel.org,
        linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org,
        quic_krichai@quicinc.com, johan+linaro@kernel.org, steev@kali.org
Subject: Re: [PATCH 1/1] PCI: qcom: Add support for system suspend and resume
Message-ID: <Y7yYN1yGxqquR1FI@google.com>
References: <20230103074907.12784-1-manivannan.sadhasivam@linaro.org>
 <20230103074907.12784-2-manivannan.sadhasivam@linaro.org>
 <dad3aba3-a40b-8b76-c689-3dc877800263@ti.com>
 <20230105133639.GC4463@thinkpad>
 <Y7hlr3x9IrT/Kg82@google.com>
 <20230106190252.GA485076@thinkpad>
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On Sat, Jan 07, 2023 at 12:32:52AM +0530, Manivannan Sadhasivam wrote:
> On Fri, Jan 06, 2023 at 06:17:19PM +0000, Matthias Kaehlcke wrote:
> > On Thu, Jan 05, 2023 at 07:06:39PM +0530, Manivannan Sadhasivam wrote:
> > > On Tue, Jan 03, 2023 at 04:46:11PM +0530, Dhruva Gole wrote:
> > > > 
> > > > 
> > > > On 03/01/23 13:19, Manivannan Sadhasivam wrote:
> > > > > During the system suspend, vote for minimal interconnect bandwidth and
> > > > > also turn OFF the resources like clock and PHY if there are no active
> > > > > devices connected to the controller. For the controllers with active
> > > > > devices, the resources are kept ON as removing the resources will
> > > > > trigger access violation during the late end of suspend cycle as kernel
> > > > > tries to access the config space of PCIe devices to mask the MSIs.
> > > > > 
> > > > > Also, it is not desirable to put the link into L2/L3 state as that
> > > > > implies VDD supply will be removed and the devices may go into powerdown
> > > > > state. This will affect the lifetime of storage devices like NVMe.
> > > > > 
> > > > > And finally, during resume, turn ON the resources if the controller was
> > > > > truly suspended (resources OFF) and update the interconnect bandwidth
> > > > > based on PCIe Gen speed.
> > > > > 
> > > > > Suggested-by: Krishna chaitanya chundru <quic_krichai@quicinc.com>
> > > > > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> > > > > ---
> > > > 
> > > > Nice to have another driver added to the list of system suspend
> > > > support!
> > > > 
> > > > Acked-by: Dhruva Gole <d-gole@ti.com>
> > > > 
> > > > >   drivers/pci/controller/dwc/pcie-qcom.c | 52 ++++++++++++++++++++++++++
> > > > >   1 file changed, 52 insertions(+)
> > > > > 
> > > > > diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> > > > > index 5696e327795b..48810f1f2dba 100644
> > > > > --- a/drivers/pci/controller/dwc/pcie-qcom.c
> > > > > +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> > > > > @@ -227,6 +227,7 @@ struct qcom_pcie {
> > > > >   	struct gpio_desc *reset;
> > > > >   	struct icc_path *icc_mem;
> > > > >   	const struct qcom_pcie_cfg *cfg;qcom_pcie_icc_update
> > > > > +	bool suspended;
> > > > >   };
> > > > >   #define to_qcom_pcie(x)		dev_get_drvdata((x)->dev)
> > > > > @@ -1835,6 +1836,52 @@ static int qcom_pcie_remove(struct platform_device *pdev)
> > > > >   	return 0;
> > > > >   }
> > > > > +static int qcom_pcie_suspend_noirq(struct device *dev)
> > > > > +{
> > > > > +	struct qcom_pcie *pcie = dev_get_drvdata(dev);
> > > > > +	int ret;
> > > > > +
> > > > > +	ret = icc_set_bw(pcie->icc_mem, 0, 0);
> > > > > +	if (ret) {
> > > > > +		dev_err(pcie->pci->dev, "Failed to set interconnect bandwidth: %d\n", ret);
> > > > > +		return ret;
> > > > > +	}
> > > > > +
> > > > > +	/*
> > > > > +	 * Turn OFF the resources only for controllers without active PCIe devices. For controllers
> > > > > +	 * with active devices, the resources are kept ON and the link is expected to be in L0/L1
> > > > > +	 * (sub)states.
> > > > > +	 *
> > > > > +	 * Turning OFF the resources for controllers with active PCIe devices will trigger access
> > > > > +	 * violation during the end of the suspend cycle, as kernel tries to access the PCIe devices
> > > > > +	 * config space for masking MSIs.
> > > > > +	 *
> > > > > +	 * Also, it is not desirable to put the link into L2/L3 state as that implies VDD supply
> > > > > +	 * will be removed and the devices may go into powerdown state. This will affect the
> > > > > +	 * lifetime of the storage devices like NVMe.
> > > > > +	 */
> > > > > +	if (!dw_pcie_link_up(pcie->pci)) {
> > > > > +		qcom_pcie_host_deinit(&pcie->pci->pp);
> > > > > +		pcie->suspended = true;
> > > > > +	}
> > > > > +
> > > > > +	return 0;
> > > > > +}
> > > > > +
> > > > > +static int qcom_pcie_resume_noirq(struct device *dev)
> > > > > +{
> > > > > +	struct qcom_pcie *pcie = dev_get_drvdata(dev);
> > > > > +
> > > > > +	if (pcie->suspended) {
> > > > > +		qcom_pcie_host_init(&pcie->pci->pp);
> > > > > +		pcie->suspended = false;
> > > > > +	}
> > > > > +
> > > > > +	qcom_pcie_icc_update(pcie);
> > > > > +
> > > > > +	return 0;
> > > > > +}
> > > > > +
> > > > >   static const struct of_device_id qcom_pcie_match[] = {
> > > > >   	{ .compatible = "qcom,pcie-apq8064", .data = &cfg_2_1_0 },
> > > > >   	{ .compatible = "qcom,pcie-apq8084", .data = &cfg_1_0_0 },
> > > > > @@ -1870,12 +1917,17 @@ DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_QCOM, 0x0302, qcom_fixup_class);
> > > > >   DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_QCOM, 0x1000, qcom_fixup_class);
> > > > >   DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_QCOM, 0x1001, qcom_fixup_class);
> > > > > +static const struct dev_pm_ops qcom_pcie_pm_ops = {
> > > > > +	NOIRQ_SYSTEM_SLEEP_PM_OPS(qcom_pcie_suspend_noirq, qcom_pcie_resume_noirq)
> > > > > +};
> > > > > +
> > > > >   static struct platform_driver qcom_pcie_driver = {
> > > > >   	.probe = qcom_pcie_probe,
> > > > >   	.remove = qcom_pcie_remove,
> > > > >   	.driver = {
> > > > >   		.name = "qcom-pcie",
> > > > >   		.of_match_table = qcom_pcie_match,
> > > > > +		.pm = &qcom_pcie_pm_ops,
> > > > >   	},
> > > > >   };
> > > > >   module_platform_driver(qcom_pcie_driver);
> > > > 
> > > > Out of curiosity, were you able to measure how much power you were able
> > > > to save after adding suspend support for PCIe? I don't know if clock
> > > > gating really saves much amount of power, but yeah its true that we
> > > > can't really cut off the power domain entirely in this case.
> > > > 
> > > 
> > > I did not measure the power consumption and I agree that we won't save much
> > > power with setting icc bandwidth to 0. But it is better to have something
> > > than nothing. And in the coming days, I have plans to look into other power
> > > saving measures also.
> > 
> > On a sc7280 system I see a reduction of ~30mW with this patch when no PCI
> > card is plugged in. The reduction seems to come from powering the PHY down.
> > 
> 
> Thanks a lot for testing!
> 
> > Interestingly on that system power consumption during suspend (without this
> > patch) is ~30mW higher *without* a PCI card vs. with a card. Maybe the PHY
> > doesn't enter a low power mode when no card is plugged in?
> 
> Yeah, both PHY and controllers are never put into low power mode even if there
> are no devices connected. I don't know if the low power mode is possible at
> all with PHY.

It's still interesting that the PHY apparently at least enters a *lower* power
mode when a card is plugged in, the extra 30mW are only seen without a card.