RE: [PATCH 3/3] PCI: imx: add compliance tests mode to enable measure signal quality

-----Original Message-----
From: Lucas Stach <l.stach@pengutronix.de>
Sent: Wednesday, September 8, 2021 4:34 PM
To: Richard Zhu <hongxing.zhu@nxp.com>; bhelgaas@google.com;
lorenzo.pieralisi@arm.com
Cc: linux-pci@vger.kernel.org; dl-linux-imx <redacted>;
linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org;
kernel@pengutronix.de
Subject: Re: [PATCH 3/3] PCI: imx: add compliance tests mode to enable
measure signal quality

Hi Richard,

Am Mittwoch, dem 08.09.2021 um 14:59 +0800 schrieb Richard Zhu:

quoted

Refer to the system board signal Quality of PCIe archiecture PHY test
specification. Signal quality tests can be executed with devices in
the polling.compliance state.

To let the device support polling.compliance stat, the clocks and
powers shouldn't be turned off during the compliance tests although
the PHY link might be down.
Add the i.MX PCIe compliance tests mode enable option to keep the and
powers on, and finish the driver probe without error return.

Use the "pcie_cmp_enabled=yes" in kernel command line to enable the
compliance tests mode.

Adding "random" kernel command line options isn't going to fly. If at all, this
should be a module_param so it gets properly namespaced. Also this needs a
more descriptive name, right now this is abbreviating the one thing that would
tell a user what this is about: compliance testing.

[Richard Zhu] Thanks a lot for your review comments.
Okay, I would use the module_param replace the command line option.
And Would add more compliance tests descriptions(what's compliance used for,
 and the simple scope of the tests) later.

quoted

Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
---
 drivers/pci/controller/dwc/pci-imx6.c | 41
+++++++++++++++++++++------
 1 file changed, 33 insertions(+), 8 deletions(-)

diff --git a/drivers/pci/controller/dwc/pci-imx6.c

b/drivers/pci/controller/dwc/pci-imx6.c
index 129928e42f84..3aef0e86f1c2 100644

--- a/drivers/pci/controller/dwc/pci-imx6.c
+++ b/drivers/pci/controller/dwc/pci-imx6.c

@@ -143,6 +143,7 @@ struct imx6_pcie {
 #define PHY_RX_OVRD_IN_LO_RX_DATA_EN		BIT(5)
 #define PHY_RX_OVRD_IN_LO_RX_PLL_EN		BIT(3)

+static int imx6_pcie_cmp_enabled;
 static int imx6_pcie_clk_enable(struct imx6_pcie *imx6_pcie);  static

void imx6_pcie_clk_disable(struct imx6_pcie *imx6_pcie);

@@ -748,10 +749,12 @@ static int imx6_pcie_start_link(struct dw_pcie

*pci)

quoted

 	 * started in Gen2 mode, there is a possibility the devices on the
 	 * bus will not be detected at all.  This happens with PCIe switches.
 	 */
-	tmp = dw_pcie_readl_dbi(pci, offset + PCI_EXP_LNKCAP);
-	tmp &= ~PCI_EXP_LNKCAP_SLS;
-	tmp |= PCI_EXP_LNKCAP_SLS_2_5GB;
-	dw_pcie_writel_dbi(pci, offset + PCI_EXP_LNKCAP, tmp);
+	if (!imx6_pcie_cmp_enabled) {
+		tmp = dw_pcie_readl_dbi(pci, offset + PCI_EXP_LNKCAP);
+		tmp &= ~PCI_EXP_LNKCAP_SLS;
+		tmp |= PCI_EXP_LNKCAP_SLS_2_5GB;
+		dw_pcie_writel_dbi(pci, offset + PCI_EXP_LNKCAP, tmp);
+	}

 	/* Start LTSSM. */
 	imx6_pcie_ltssm_enable(dev);

@@ -812,9 +815,12 @@ static int imx6_pcie_start_link(struct dw_pcie

*pci)

quoted

 		dw_pcie_readl_dbi(pci, PCIE_PORT_DEBUG0),
 		dw_pcie_readl_dbi(pci, PCIE_PORT_DEBUG1));
 	imx6_pcie_reset_phy(imx6_pcie);
-	imx6_pcie_clk_disable(imx6_pcie);
-	if (imx6_pcie->vpcie && regulator_is_enabled(imx6_pcie->vpcie) > 0)
-		regulator_disable(imx6_pcie->vpcie);
+	if (!imx6_pcie_cmp_enabled) {
+		imx6_pcie_clk_disable(imx6_pcie);
+		if (imx6_pcie->vpcie
+		    && regulator_is_enabled(imx6_pcie->vpcie) > 0)
+			regulator_disable(imx6_pcie->vpcie);
+	}
 	return ret;
 }

@@ -1010,6 +1016,17 @@ static const struct dev_pm_ops

imx6_pcie_pm_ops = {

quoted

 				      imx6_pcie_resume_noirq)
 };

+static int __init imx6_pcie_compliance_test_enable(char *str) {
+	if (!strcmp(str, "yes")) {
+		pr_info("Enable the i.MX PCIe TX/CLK compliance tests mode.\n");
+		imx6_pcie_cmp_enabled = 1;
+	}
+	return 1;
+}
+
+__setup("pcie_cmp_enabled=", imx6_pcie_compliance_test_enable);
+
 static int imx6_pcie_probe(struct platform_device *pdev)  {
 	struct device *dev = &pdev->dev;

@@ -1187,8 +1204,16 @@ static int imx6_pcie_probe(struct

platform_device *pdev)

quoted

 		return ret;

 	ret = dw_pcie_host_init(&pci->pp);
-	if (ret < 0)
+	if (ret < 0) {
+		if (imx6_pcie_cmp_enabled) {
+			/* The PCIE clocks and powers wouldn't be turned off */
+			dev_info(dev, "To do the compliance tests.\n");

This needs a better message, like "Driver loaded with compliance test mode
enabled" and the message needs to be shown unconditionally, not only when
the host init fails. We don't want to have the user track down weird issues
when the compliance test option was specified by accident and the link is
almost working due to this.

[Richard Zhu] Thanks. Ok, got that, would update the message in next version.

Best Regards
Richard Zhu

Regards,
Lucas

quoted

+			ret = 0;
+		} else {
+			dev_err(dev, "Unable to add pcie port.\n");
+		}
 		return ret;
+	}

 	if (pci_msi_enabled()) {
 		u8 offset = dw_pcie_find_capability(pci, PCI_CAP_ID_MSI);

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