[PATCH v4 2/2] PCI: amd-mdb: Add support for PCIe RP PERST# signal handling

[Sai Krishna Musham <sai.krishna.musham@amd.com>]

Add support for handling the AMD Versal Gen 2 MDB PCIe Root Port PERST#
signal via a GPIO by parsing the new PCIe bridge node to acquire the
reset GPIO.

As part of this, update the interrupt controller node parsing to use
of_get_child_by_name() instead of of_get_next_child(), since the PCIe
node now has multiple children. This ensures the correct node is
selected during initialization.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202506241020.rPD1a2Vr-lkp@intel.com/
Signed-off-by: Sai Krishna Musham <sai.krishna.musham@amd.com>
---
Changes in v4:
- Resolve kernel test robot warning.
https://lore.kernel.org/oe-kbuild-all/202506241020.rPD1a2Vr-lkp@intel.com/
- Update commit message.

Changes in v3:
- Implement amd_mdb_parse_pcie_port to parse bridge node for reset-gpios property.

Changes in v2:
- Change delay to PCIE_T_PVPERL_MS

v3 https://lore.kernel.org/r/20250618080931.2472366-1-sai.krishna.musham@amd.com/
v2 https://lore.kernel.org/r/20250429090046.1512000-1-sai.krishna.musham@amd.com/
v1 https://lore.kernel.org/r/20250326041507.98232-1-sai.krishna.musham@amd.com/
---
 drivers/pci/controller/dwc/pcie-amd-mdb.c | 46 ++++++++++++++++++++++-
 1 file changed, 45 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/controller/dwc/pcie-amd-mdb.c b/drivers/pci/controller/dwc/pcie-amd-mdb.c
index 9f7251a16d32..f011a83550b9 100644
--- a/drivers/pci/controller/dwc/pcie-amd-mdb.c
+++ b/drivers/pci/controller/dwc/pcie-amd-mdb.c
@@ -18,6 +18,7 @@
 #include <linux/resource.h>
 #include <linux/types.h>
 
+#include "../../pci.h"
 #include "pcie-designware.h"
 
 #define AMD_MDB_TLP_IR_STATUS_MISC		0x4C0
@@ -56,6 +57,7 @@
  * @slcr: MDB System Level Control and Status Register (SLCR) base
  * @intx_domain: INTx IRQ domain pointer
  * @mdb_domain: MDB IRQ domain pointer
+ * @perst_gpio: GPIO descriptor for PERST# signal handling
  * @intx_irq: INTx IRQ interrupt number
  */
 struct amd_mdb_pcie {
@@ -63,6 +65,7 @@ struct amd_mdb_pcie {
 	void __iomem			*slcr;
 	struct irq_domain		*intx_domain;
 	struct irq_domain		*mdb_domain;
+	struct gpio_desc		*perst_gpio;
 	int				intx_irq;
 };
 
@@ -284,7 +287,7 @@ static int amd_mdb_pcie_init_irq_domains(struct amd_mdb_pcie *pcie,
 	struct device_node *pcie_intc_node;
 	int err;
 
-	pcie_intc_node = of_get_next_child(node, NULL);
+	pcie_intc_node = of_get_child_by_name(node, "interrupt-controller");
 	if (!pcie_intc_node) {
 		dev_err(dev, "No PCIe Intc node found\n");
 		return -ENODEV;
@@ -402,6 +405,34 @@ static int amd_mdb_setup_irq(struct amd_mdb_pcie *pcie,
 	return 0;
 }
 
+static int amd_mdb_parse_pcie_port(struct amd_mdb_pcie *pcie)
+{
+	struct device *dev = pcie->pci.dev;
+	struct device_node *pcie_port_node;
+
+	pcie_port_node = of_get_next_child_with_prefix(dev->of_node, NULL, "pcie");
+	if (!pcie_port_node) {
+		dev_err(dev, "No PCIe Bridge node found\n");
+		return -ENODEV;
+	}
+
+	/* Request the GPIO for PCIe reset signal and assert */
+	pcie->perst_gpio = devm_fwnode_gpiod_get(dev, of_fwnode_handle(pcie_port_node),
+						 "reset", GPIOD_OUT_HIGH, NULL);
+	if (IS_ERR(pcie->perst_gpio)) {
+		if (PTR_ERR(pcie->perst_gpio) != -ENOENT) {
+			of_node_put(pcie_port_node);
+			return dev_err_probe(dev, PTR_ERR(pcie->perst_gpio),
+					     "Failed to request reset GPIO\n");
+		}
+		pcie->perst_gpio = NULL;
+	}
+
+	of_node_put(pcie_port_node);
+
+	return 0;
+}
+
 static int amd_mdb_add_pcie_port(struct amd_mdb_pcie *pcie,
 				 struct platform_device *pdev)
 {
@@ -426,6 +457,14 @@ static int amd_mdb_add_pcie_port(struct amd_mdb_pcie *pcie,
 
 	pp->ops = &amd_mdb_pcie_host_ops;
 
+	if (pcie->perst_gpio) {
+		mdelay(PCIE_T_PVPERL_MS);
+
+		/* Deassert the reset signal */
+		gpiod_set_value_cansleep(pcie->perst_gpio, 0);
+		mdelay(PCIE_T_RRS_READY_MS);
+	}
+
 	err = dw_pcie_host_init(pp);
 	if (err) {
 		dev_err(dev, "Failed to initialize host, err=%d\n", err);
@@ -444,6 +483,7 @@ static int amd_mdb_pcie_probe(struct platform_device *pdev)
 	struct device *dev = &pdev->dev;
 	struct amd_mdb_pcie *pcie;
 	struct dw_pcie *pci;
+	int ret;
 
 	pcie = devm_kzalloc(dev, sizeof(*pcie), GFP_KERNEL);
 	if (!pcie)
@@ -454,6 +494,10 @@ static int amd_mdb_pcie_probe(struct platform_device *pdev)
 
 	platform_set_drvdata(pdev, pcie);
 
+	ret = amd_mdb_parse_pcie_port(pcie);
+	if (ret)
+		return ret;
+
 	return amd_mdb_add_pcie_port(pcie, pdev);
 }
 
-- 
2.44.1