[PATCH v4 2/2] PCI: layerscape: Add the workaround for lost link capabilities during reset.

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From: Xiaowei Bao <xiaowei.bao@xxxxxxx>

A workaround for the issue where the PCI Express Endpoint (EP) controller
loses the values of the Maximum Link Width and Supported Link Speed from
the Link Capabilities Register, which initially configured by the Reset
Configuration Word (RCW) during a link-down or hot reset event.

Fixes: a805770d8a22 ("PCI: layerscape: Add EP mode support")
Acked-by: Manivannan Sadhasivam <mani@xxxxxxxxxx>
Signed-off-by: Xiaowei Bao <xiaowei.bao@xxxxxxx>
Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@xxxxxxx>
Signed-off-by: Frank Li <Frank.Li@xxxxxxx>
change from v3 to v4
 - fix wrong commit a debug code, change pr_err to pr_dbg
change from v2 to v3
 - fix subject typo capabilities
change from v1 to v2:
 - add comments at restore register
 - add fixes tag
 - dw_pcie_writew_dbi to dw_pcie_writel_dbi

 .../pci/controller/dwc/pci-layerscape-ep.c    | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/pci/controller/dwc/pci-layerscape-ep.c b/drivers/pci/controller/dwc/pci-layerscape-ep.c
index e0969ff2ddf7..b1faf41a2fae 100644
--- a/drivers/pci/controller/dwc/pci-layerscape-ep.c
+++ b/drivers/pci/controller/dwc/pci-layerscape-ep.c
@@ -45,6 +45,7 @@ struct ls_pcie_ep {
 	struct pci_epc_features		*ls_epc;
 	const struct ls_pcie_ep_drvdata *drvdata;
 	int				irq;
+	u32				lnkcap;
 	bool				big_endian;
@@ -73,6 +74,7 @@ static irqreturn_t ls_pcie_ep_event_handler(int irq, void *dev_id)
 	struct ls_pcie_ep *pcie = dev_id;
 	struct dw_pcie *pci = pcie->pci;
 	u32 val, cfg;
+	u8 offset;
 	val = ls_lut_readl(pcie, PEX_PF0_PME_MES_DR);
 	ls_lut_writel(pcie, PEX_PF0_PME_MES_DR, val);
@@ -81,6 +83,19 @@ static irqreturn_t ls_pcie_ep_event_handler(int irq, void *dev_id)
 		return IRQ_NONE;
 	if (val & PEX_PF0_PME_MES_DR_LUD) {
+		offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
+		/*
+		 * The values of the Maximum Link Width and Supported Link
+		 * Speed from the Link Capabilities Register will be lost
+		 * during link down or hot reset. Restore initial value
+		 * that configured by the Reset Configuration Word (RCW).
+		 */
+		dw_pcie_dbi_ro_wr_en(pci);
+		dw_pcie_writel_dbi(pci, offset + PCI_EXP_LNKCAP, pcie->lnkcap);
+		dw_pcie_dbi_ro_wr_dis(pci);
 		cfg = ls_lut_readl(pcie, PEX_PF0_CONFIG);
 		cfg |= PEX_PF0_CFG_READY;
 		ls_lut_writel(pcie, PEX_PF0_CONFIG, cfg);
@@ -216,6 +231,7 @@ static int __init ls_pcie_ep_probe(struct platform_device *pdev)
 	struct ls_pcie_ep *pcie;
 	struct pci_epc_features *ls_epc;
 	struct resource *dbi_base;
+	u8 offset;
 	int ret;
 	pcie = devm_kzalloc(dev, sizeof(*pcie), GFP_KERNEL);
@@ -252,6 +268,9 @@ static int __init ls_pcie_ep_probe(struct platform_device *pdev)
 	platform_set_drvdata(pdev, pcie);
+	offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
+	pcie->lnkcap = dw_pcie_readl_dbi(pci, offset + PCI_EXP_LNKCAP);
 	ret = dw_pcie_ep_init(&pci->ep);
 	if (ret)
 		return ret;

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