Date:   Fri, 18 Mar 2022 20:04:30 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Prasad Malisetty <quic_pmaliset@...cinc.com>
Cc:     agross@...nel.org, bjorn.andersson@...aro.org,
        lorenzo.pieralisi@....com, robh@...nel.org, kw@...ux.com,
        bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        rajatja@...gle.com, refactormyself@...il.com,
        quic_vbadigan@...cinc.com, quic_ramkri@...cinc.com,
        swboyd@...omium.org
Subject: Re: [PATCH v4] PCI: qcom: Add system PM support

On Tue, Mar 08, 2022 at 12:25:06AM +0530, Prasad Malisetty wrote:
> Add suspend_noirq and resume_noirq callbacks to handle
> system suspend and resume in dwc PCIe controller driver.
> 
> When system suspends, send PME turnoff message to enter
> link into L2 state. Along with powerdown the PHY, disable
> pipe clock, switch gcc_pcie_1_pipe_clk_src to XO if mux is
> supported and disable the pcie clocks, regulators.
> 
> When system resumes, PCIe link will be re-established and
> setup rc settings.
> 
> Signed-off-by: Prasad Malisetty <quic_pmaliset@...cinc.com>
> 
> ---
> Changes since v3:
> 	- Replaced noirq hooks with normal suspend/resume hooks.
> 	- Removed local variable and placed in function itself.
> 
> Changes since v2:
> 	- Removed unnecessary variable initializations and comments.
> 	- Removed platform specific variables declarations.
> 	- Added MACRO names for the BIT shiftings.
> 
> Changes since v1:
> 	- Removed unnecessary logs and modified log level suggested by Manivannan.
> 	- Removed platform specific callbacks as PM support is generic.
> ---
>  drivers/pci/controller/dwc/pcie-qcom.c | 97 ++++++++++++++++++++++++++++++++++
>  1 file changed, 97 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> index 6ab9089..4d29c80 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> @@ -48,6 +48,7 @@
>  #define PCIE20_PARF_PHY_REFCLK			0x4C
>  #define PHY_REFCLK_SSP_EN			BIT(16)
>  #define PHY_REFCLK_USE_PAD			BIT(12)
> +#define PHY_POWER_DOWN				0x1

BIT(0)

>  
>  #define PCIE20_PARF_DBI_BASE_ADDR		0x168
>  #define PCIE20_PARF_SLV_ADDR_SPACE_SIZE		0x16C
> @@ -62,6 +63,8 @@
>  
>  #define PCIE20_ELBI_SYS_CTRL			0x04
>  #define PCIE20_ELBI_SYS_CTRL_LT_ENABLE		BIT(0)
> +#define PCIE_PME_TURNOFF_MSG			BIT(4)
> +#define PCIE_PM_LINKST_IN_L2			BIT(5)
>  
>  #define PCIE20_AXI_MSTR_RESP_COMP_CTRL0		0x818
>  #define CFG_REMOTE_RD_REQ_BRIDGE_SIZE_2K	0x4
> @@ -73,6 +76,8 @@
>  
>  #define PCIE20_PARF_Q2A_FLUSH			0x1AC
>  
> +#define PCIE20_PARF_PM_STTS			0x24
> +
>  #define PCIE20_MISC_CONTROL_1_REG		0x8BC
>  #define DBI_RO_WR_EN				1
>  
> @@ -1645,6 +1650,97 @@ static int qcom_pcie_probe(struct platform_device *pdev)
>  	return ret;
>  }
>  
> +static int qcom_pcie_send_pme_turnoff_msg(struct qcom_pcie *pcie)
> +{
> +	int ret;
> +	u32 val, poll_val;
> +	struct dw_pcie *pci = pcie->pci;
> +	struct device *dev = pci->dev;
> +
> +	val = readl(pcie->elbi + PCIE20_ELBI_SYS_CTRL);
> +	val |= PCIE_PME_TURNOFF_MSG;
> +	writel(val, pcie->elbi + PCIE20_ELBI_SYS_CTRL);
> +
> +	ret = readl_poll_timeout((pcie->parf + PCIE20_PARF_PM_STTS), poll_val,
> +			(poll_val & PCIE_PM_LINKST_IN_L2),
> +			10000, 100000);
> +	if (!ret)
> +		dev_dbg(dev, "Device entered L23_Ready state\n");
> +	else
> +		dev_err(dev, "Device failed to enter L23_Ready. PM_STTS 0x%x\n",
> +			readl_relaxed(pcie->parf + PCIE20_PARF_PM_STTS));
> +
> +	return ret;
> +}
> +
> +static void qcom_pcie_host_disable(struct qcom_pcie *pcie)
> +{
> +	qcom_ep_reset_assert(pcie);
> +

In the modem usecase, the endpoint uses the LINK_DOWN event for freeing up the
resources. If PERST# gets asserted before turing off the PHY, the LINK_DOWN
event will be missed in the endpoint. And moreover, modem cannot free up the
resources in PERST# handler as it is a hard IRQ handler and the cleanup action
might sleep. The deferring also doesn't work because, once PERST# event get's
handled, the host will turn off the refclk and the access to DBI region will
not be allowed.

For this reason, I'd prefer to move this PERST# assertion to the end of the
funtion.

> +	/* Put PHY into POWER DOWN state */
> +	phy_power_off(pcie->phy);
> +
> +	writel(PHY_POWER_DOWN, pcie->parf + PCIE20_PARF_PHY_CTRL);
> +
> +	if (pcie->cfg->ops->post_deinit)
> +		pcie->cfg->ops->post_deinit(pcie);
> +
> +	/* Disable PCIe clocks and regulators */
> +	pcie->cfg->ops->deinit(pcie);

It is also required to add a 100ms delay here as PERST# reaches quickly before
LINK_DOWN.


	/*
	 * Allow the LINK_DOWN event to reach the endpoint before PERST# assert.
	 * This is required for resource cleanup in the endpoint for modem usecase.
	 */
	usleep_range(50000, 100000);
	qcom_ep_reset_assert(pcie);

> +}
> +
> +static int __maybe_unused qcom_pcie_pm_suspend(struct device *dev)
> +{
> +	int ret;
> +	struct qcom_pcie *pcie = dev_get_drvdata(dev);
> +	struct dw_pcie *pci = pcie->pci;
> +
> +	if (!dw_pcie_link_up(pci)) {
> +		dev_dbg(dev, "Power has been turned off already\n");

I think this debug message doesn't add any value, so just skip it.

> +		return 0;
> +	}
> +
> +	ret = qcom_pcie_send_pme_turnoff_msg(pcie);
> +	if (ret)
> +		return ret;
> +
> +	/* Power down the PHY, disable clock and regulators */

You are also asserting PERST#.

> +	qcom_pcie_host_disable(pcie);
> +
> +	return 0;
> +}
> +
> +/* Resume the PCIe link */
> +static int __maybe_unused qcom_pcie_pm_resume(struct device *dev)
> +{
> +	int ret;
> +	struct qcom_pcie *pcie = dev_get_drvdata(dev);
> +	struct dw_pcie *pci = pcie->pci;
> +	struct pcie_port *pp = &pci->pp;
> +
> +	ret = qcom_pcie_host_init(pp);
> +	if (ret) {
> +		dev_err(dev, "cannot initialize host\n");
> +		return ret;
> +	}
> +
> +	dw_pcie_setup_rc(pp);
> +
> +	qcom_pcie_start_link(pci);
> +
> +	ret = dw_pcie_wait_for_link(pci);
> +	if (ret) {
> +		dev_err(dev, "Link never came up, Resume failed\n");

dw_pcie_wait_for_link() itself prints the error in failure case. So just return
directly.

	return dw_pcie_wait_for_link(pci);

Thanks,
Mani

> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +static const struct dev_pm_ops qcom_pcie_pm_ops = {
> +	SET_SYSTEM_SLEEP_PM_OPS(qcom_pcie_pm_suspend, qcom_pcie_pm_resume)
> +};
> +
>  static const struct of_device_id qcom_pcie_match[] = {
>  	{ .compatible = "qcom,pcie-apq8084", .data = &apq8084_cfg },
>  	{ .compatible = "qcom,pcie-ipq8064", .data = &ipq8064_cfg },
> @@ -1679,6 +1775,7 @@ static struct platform_driver qcom_pcie_driver = {
>  	.probe = qcom_pcie_probe,
>  	.driver = {
>  		.name = "qcom-pcie",
> +		.pm = &qcom_pcie_pm_ops,
>  		.suppress_bind_attrs = true,
>  		.of_match_table = qcom_pcie_match,
>  	},
> -- 
> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member 
> of Code Aurora Forum, hosted by The Linux Foundation
> 

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