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

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Date:   Tue, 3 Jan 2023 16:46:11 +0530
From:   Dhruva Gole <d-gole@...com>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        <lpieralisi@...nel.org>, <robh@...nel.org>
CC:     <andersson@...nel.org>, <konrad.dybcio@...aro.org>, <kw@...ux.com>,
        <bhelgaas@...gle.com>, <linux-pci@...r.kernel.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <quic_krichai@...cinc.com>, <johan+linaro@...nel.org>,
        <steev@...i.org>
Subject: Re: [PATCH 1/1] PCI: qcom: Add support for system suspend and resume



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@...cinc.com>
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> ---

Nice to have another driver added to the list of system suspend
support!

Acked-by: Dhruva Gole <d-gole@...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