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

Dhruva Gole
2023-01-03T11:16:37Z

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.

--
Thanks and Regards,
Dhruva Gole