PCI: dw-rockchip: Implement .reset_root_port() and use for link down

The PCIe link may go down in cases like firmware crashes or unstable
connections. When this occurs, the Root Port must be reset to restore the
functionality. However, the current driver lacks link down handling,
forcing users to reboot the system to recover.

Implement the .reset_root_port() callback for link down handling for the
Rockchip DWC PCIe host controller. The RC is reset, reconfigured, and link
training initiated to recover from the link down event.

This also by extension fixes issues with sysfs-initiated bus resets.
Currently, the endpoint device is non-functional after a sysfs initiated
bus reset (it may link up with downgraded link status).  With the link down
handling support, a sysfs initiated bus reset works as intended. Testing
conducted on a ROCK5B board with an M.2 NVMe drive.

Signed-off-by: Wilfred Mallawa <wilfred.mallawa@wdc.com>
Signed-off-by: Niklas Cassel <cassel@kernel.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@oss.qualcomm.com>
[bhelgaas: subject]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://patch.msgid.link/20260727172654.605988-4-cassel@kernel.org

drivers/pci/controller/dwc/Kconfig

@@ -374,6 +374,7 @@ config PCIE_ROCKCHIP_DW_HOST
 	depends on OF
 	select PCIE_DW_HOST
 	select PCIE_ROCKCHIP_DW
+	select PCI_HOST_COMMON
 	help
 	  Enables support for the DesignWare PCIe controller in the
 	  Rockchip SoC (except RK3399) to work in host mode.

drivers/pci/controller/dwc/pcie-dw-rockchip.c

@@ -26,6 +26,7 @@
 #include <trace/events/pci_controller.h>
 
 #include "../../pci.h"
+#include "../pci-host-common.h"
 #include "pcie-designware.h"
 
 /*
@@ -122,6 +123,9 @@ struct rockchip_pcie_of_data {
 	const struct pci_epc_features *epc_features;
 };
 
+static int rockchip_pcie_rc_reset_root_port(struct pci_host_bridge *bridge,
+				       struct pci_dev *pdev);
+
 static int rockchip_pcie_readl_apb(struct rockchip_pcie *rockchip, u32 reg)
 {
 	return readl_relaxed(rockchip->apb_base + reg);
@@ -436,6 +440,7 @@ static int rockchip_pcie_host_init(struct dw_pcie_rp *pp)
 
 	rockchip_pcie_configure_l1ss(pci);
 	rockchip_pcie_enable_l0s(pci);
+	pp->bridge->reset_root_port = rockchip_pcie_rc_reset_root_port;
 
 	/* Disable Root Ports BAR0 and BAR1 as they report bogus size */
 	dw_pcie_writel_dbi2(pci, PCI_BASE_ADDRESS_0, 0x0);
@@ -634,6 +639,32 @@ static const struct dw_pcie_ops dw_pcie_ops = {
 	.get_ltssm = rockchip_pcie_get_ltssm,
 };
 
+static irqreturn_t rockchip_pcie_rc_sys_irq_thread(int irq, void *arg)
+{
+	struct rockchip_pcie *rockchip = arg;
+	struct dw_pcie *pci = &rockchip->pci;
+	struct dw_pcie_rp *pp = &pci->pp;
+	struct device *dev = pci->dev;
+	struct pci_dev *port;
+	u32 reg;
+
+	reg = rockchip_pcie_readl_apb(rockchip, PCIE_CLIENT_INTR_STATUS_MISC);
+	rockchip_pcie_writel_apb(rockchip, reg, PCIE_CLIENT_INTR_STATUS_MISC);
+
+	dev_dbg(dev, "PCIE_CLIENT_INTR_STATUS_MISC: %#x\n", reg);
+	dev_dbg(dev, "LTSSM_STATUS: %#x\n", rockchip_pcie_get_ltssm_reg(rockchip));
+
+	if (reg & PCIE_LINK_REQ_RST_NOT_INT) {
+		dev_dbg(dev, "hot reset or link-down reset\n");
+		for_each_pci_bridge(port, pp->bridge->bus) {
+			if (pci_pcie_type(port) == PCI_EXP_TYPE_ROOT_PORT)
+				pci_host_handle_link_down(port);
+		}
+	}
+
+	return IRQ_HANDLED;
+}
+
 static irqreturn_t rockchip_pcie_ep_sys_irq_thread(int irq, void *arg)
 {
 	struct rockchip_pcie *rockchip = arg;
@@ -666,14 +697,29 @@ static irqreturn_t rockchip_pcie_ep_sys_irq_thread(int irq, void *arg)
 	return IRQ_HANDLED;
 }
 
-static int rockchip_pcie_configure_rc(struct rockchip_pcie *rockchip)
+static int rockchip_pcie_configure_rc(struct platform_device *pdev,
+				      struct rockchip_pcie *rockchip)
 {
+	struct device *dev = &pdev->dev;
 	struct dw_pcie_rp *pp;
+	int irq, ret;
 	u32 val;
 
 	if (!IS_ENABLED(CONFIG_PCIE_ROCKCHIP_DW_HOST))
 		return -ENODEV;
 
+	irq = platform_get_irq_byname(pdev, "sys");
+	if (irq < 0)
+		return irq;
+
+	ret = devm_request_threaded_irq(dev, irq, NULL,
+					rockchip_pcie_rc_sys_irq_thread,
+					IRQF_ONESHOT, "pcie-sys-rc", rockchip);
+	if (ret) {
+		dev_err(dev, "failed to request PCIe sys IRQ\n");
+		return ret;
+	}
+
 	/* LTSSM enable control mode */
 	val = FIELD_PREP_WM16(PCIE_LTSSM_ENABLE_ENHANCE, 1);
 	rockchip_pcie_writel_apb(rockchip, val, PCIE_CLIENT_HOT_RESET_CTRL);
@@ -685,7 +731,17 @@ static int rockchip_pcie_configure_rc(struct rockchip_pcie *rockchip)
 	pp = &rockchip->pci.pp;
 	pp->ops = &rockchip_pcie_host_ops;
 
-	return dw_pcie_host_init(pp);
+	ret = dw_pcie_host_init(pp);
+	if (ret) {
+		dev_err(dev, "failed to initialize host\n");
+		return ret;
+	}
+
+	/* unmask hot reset/link-down reset */
+	val = FIELD_PREP_WM16(PCIE_LINK_REQ_RST_NOT_INT, 0);
+	rockchip_pcie_writel_apb(rockchip, val, PCIE_CLIENT_INTR_MASK_MISC);
+
+	return ret;
 }
 
 static int rockchip_pcie_configure_ep(struct platform_device *pdev,
@@ -804,7 +860,7 @@ static int rockchip_pcie_probe(struct platform_device *pdev)
 
 	switch (data->mode) {
 	case DW_PCIE_RC_TYPE:
-		ret = rockchip_pcie_configure_rc(rockchip);
+		ret = rockchip_pcie_configure_rc(pdev, rockchip);
 		if (ret)
 			goto deinit_clk;
 		break;
@@ -829,6 +885,78 @@ static int rockchip_pcie_probe(struct platform_device *pdev)
 	return ret;
 }
 
+static int rockchip_pcie_rc_reset_root_port(struct pci_host_bridge *bridge,
+					    struct pci_dev *pdev)
+{
+	struct pci_bus *bus = bridge->bus;
+	struct dw_pcie_rp *pp = bus->sysdata;
+	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
+	struct rockchip_pcie *rockchip = to_rockchip_pcie(pci);
+	struct device *dev = rockchip->pci.dev;
+	u32 val;
+	int ret;
+
+	dw_pcie_stop_link(pci);
+	clk_bulk_disable_unprepare(rockchip->clk_cnt, rockchip->clks);
+	rockchip_pcie_phy_deinit(rockchip);
+
+	ret = reset_control_assert(rockchip->rst);
+	if (ret)
+		return ret;
+
+	ret = rockchip_pcie_phy_init(rockchip);
+	if (ret)
+		return ret;
+
+	ret = reset_control_deassert(rockchip->rst);
+	if (ret)
+		goto deinit_phy;
+
+	ret = rockchip_pcie_clk_init(rockchip);
+	if (ret)
+		goto deinit_phy;
+
+	ret = pp->ops->init(pp);
+	if (ret) {
+		dev_err(dev, "Host init failed: %d\n", ret);
+		goto deinit_clk;
+	}
+
+	/* LTSSM enable control mode */
+	val = FIELD_PREP_WM16(PCIE_LTSSM_ENABLE_ENHANCE, 1);
+	rockchip_pcie_writel_apb(rockchip, val, PCIE_CLIENT_HOT_RESET_CTRL);
+
+	rockchip_pcie_writel_apb(rockchip,
+				 PCIE_CLIENT_SET_MODE(PCIE_CLIENT_MODE_RC),
+				 PCIE_CLIENT_GENERAL_CON);
+
+	ret = dw_pcie_setup_rc(pp);
+	if (ret) {
+		dev_err(dev, "Failed to setup RC: %d\n", ret);
+		goto deinit_clk;
+	}
+
+	/* unmask hot reset/link-down reset */
+	val = FIELD_PREP_WM16(PCIE_LINK_REQ_RST_NOT_INT, 0);
+	rockchip_pcie_writel_apb(rockchip, val, PCIE_CLIENT_INTR_MASK_MISC);
+
+	ret = dw_pcie_start_link(pci);
+	if (ret)
+		goto deinit_clk;
+
+	/* Ignore errors, the link may come up later */
+	dw_pcie_wait_for_link(pci);
+	dev_dbg(dev, "Root Port reset completed\n");
+	return ret;
+
+deinit_clk:
+	clk_bulk_disable_unprepare(rockchip->clk_cnt, rockchip->clks);
+deinit_phy:
+	rockchip_pcie_phy_deinit(rockchip);
+
+	return ret;
+}
+
 static const struct rockchip_pcie_of_data rockchip_pcie_rc_of_data_rk3568 = {
 	.mode = DW_PCIE_RC_TYPE,
 };