Re: [PATCH 1/1] PCI: qcom: Add support for system suspend and resume

[Manivannan Sadhasivam]

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@xxxxxxxxxxx>
> > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx>
> > ---
> 
> Nice to have another driver added to the list of system suspend
> support!
> 
> Acked-by: Dhruva Gole <d-gole@xxxxxx>
> 
> >   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.

Thanks,
Mani

> -- 
> Thanks and Regards,
> Dhruva Gole

-- 
மணிவண்ணன் சதாசிவம்