linux-kernel - Re: [PATCH v2] PCI: dwc: Wait for link up only if link is started

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Message-ID: <ZC6Mov/wX4cbIiNG@google.com>
Date:   Thu, 6 Apr 2023 14:40:58 +0530
From:   Ajay Agarwal <ajayagarwal@...gle.com>
To:     William McVicker <willmcvicker@...gle.com>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Sajid Dalvi <sdalvi@...gle.com>,
        Han Jingoo <jingoohan1@...il.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Rob Herring <robh@...nel.org>, kernel-team@...roid.com,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Subject: Re: [PATCH v2] PCI: dwc: Wait for link up only if link is started

Here is my attempt at a patch which can satisfy all the requirements
(Ideally, I did not want to use `pci->ops` in the host driver but I
could not figure out any other way):

diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c
b/drivers/pci/controller/dwc/pcie-designware-host.c
index 9952057c8819..39c7219ec7c9 100644
--- a/drivers/pci/controller/dwc/pcie-designware-host.c
+++ b/drivers/pci/controller/dwc/pcie-designware-host.c
@@ -485,15 +485,18 @@ int dw_pcie_host_init(struct dw_pcie_rp *pp)
 	if (ret)
 		goto err_remove_edma;
 
-	if (!dw_pcie_link_up(pci)) {
-		ret = dw_pcie_start_link(pci);
+	ret = dw_pcie_start_link(pci);
+	if (ret)
+		goto err_remove_edma;
+
+	if (dw_pcie_link_up(pci)) {
+		dw_pcie_print_link_status(pci);
+	} else if (pci->ops && pci->ops->start_link) {
+		ret = dw_pcie_wait_for_link(pci);
 		if (ret)
-			goto err_remove_edma;
+			goto err_stop_link;
 	}
 
-	/* Ignore errors, the link may come up later */
-	dw_pcie_wait_for_link(pci);
-
 	bridge->sysdata = pp;
 
 	ret = pci_host_probe(bridge);
diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
index 53a16b8b6ac2..03748a8dffd3 100644
--- a/drivers/pci/controller/dwc/pcie-designware.c
+++ b/drivers/pci/controller/dwc/pcie-designware.c
@@ -644,9 +644,20 @@ void dw_pcie_disable_atu(struct dw_pcie *pci, u32 dir, int index)
 	dw_pcie_writel_atu(pci, dir, index, PCIE_ATU_REGION_CTRL2, 0);
 }
 
-int dw_pcie_wait_for_link(struct dw_pcie *pci)
+void dw_pcie_print_link_status(struct dw_pcie *pci)
 {
 	u32 offset, val;
+
+	offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
+	val = dw_pcie_readw_dbi(pci, offset + PCI_EXP_LNKSTA);
+
+	dev_info(pci->dev, "PCIe Gen.%u x%u link up\n",
+		 FIELD_GET(PCI_EXP_LNKSTA_CLS, val),
+		 FIELD_GET(PCI_EXP_LNKSTA_NLW, val));
+}
+
+int dw_pcie_wait_for_link(struct dw_pcie *pci)
+{
 	int retries;
 
 	/* Check if the link is up or not */
@@ -662,12 +673,7 @@ int dw_pcie_wait_for_link(struct dw_pcie *pci)
 		return -ETIMEDOUT;
 	}
 
-	offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
-	val = dw_pcie_readw_dbi(pci, offset + PCI_EXP_LNKSTA);
-
-	dev_info(pci->dev, "PCIe Gen.%u x%u link up\n",
-		 FIELD_GET(PCI_EXP_LNKSTA_CLS, val),
-		 FIELD_GET(PCI_EXP_LNKSTA_NLW, val));
+	dw_pcie_print_link_status(pci);
 
 	return 0;
 }
diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
index 79713ce075cc..615660640801 100644
--- a/drivers/pci/controller/dwc/pcie-designware.h
+++ b/drivers/pci/controller/dwc/pcie-designware.h
@@ -429,6 +429,7 @@ void dw_pcie_setup(struct dw_pcie *pci);
 void dw_pcie_iatu_detect(struct dw_pcie *pci);
 int dw_pcie_edma_detect(struct dw_pcie *pci);
 void dw_pcie_edma_remove(struct dw_pcie *pci);
+void dw_pcie_print_link_status(struct dw_pcie *pci);
 
 static inline void dw_pcie_writel_dbi(struct dw_pcie *pci, u32 reg, u32 val)
 {