[PATCH v7 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. If the bridge node is not found, fall back to acquiring it
from the PCIe host bridge node.

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
host bridge node now has multiple children. This ensures the correct
node is selected during initialization.

Signed-off-by: Sai Krishna Musham <sai.krishna.musham@amd.com>
---
Changes in v7:
- Use for_each_child_of_node_with_prefix() to iterate through PCIe
  Bridge nodes.

Changes in v6:
- Simplified error checking condition logic.
- Removed unnecessary fallback message.

Changes in v5:
- Add fall back mechanism to acquire reset GPIO from PCIe node when PCIe Bridge
node is not present.

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

v6 https://lore.kernel.org/all/20250719030951.3616385-1-sai.krishna.musham@amd.com/
v5 https://lore.kernel.org/all/20250711052357.3859719-1-sai.krishna.musham@amd.com/
v4 https://lore.kernel.org/all/20250626054906.3277029-1-sai.krishna.musham@amd.com/
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 | 52 ++++++++++++++++++++++-
 1 file changed, 51 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..3c6e837465bb 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 +405,28 @@ 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 __maybe_unused;
+
+	/*
+	 * This platform currently supports only one Root Port, so the loop
+	 * will execute only once.
+	 * TODO: Enhance the driver to handle multiple Root Ports in the future.
+	 */
+	for_each_child_of_node_with_prefix(dev->of_node, pcie_port_node, "pcie") {
+		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))
+			return dev_err_probe(dev, PTR_ERR(pcie->perst_gpio),
+					     "Failed to request reset GPIO\n");
+		return 0;
+	}
+
+	return -ENODEV;
+}
+
 static int amd_mdb_add_pcie_port(struct amd_mdb_pcie *pcie,
 				 struct platform_device *pdev)
 {
@@ -426,6 +451,12 @@ 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);
+		gpiod_set_value_cansleep(pcie->perst_gpio, 0);
+		mdelay(PCIE_RESET_CONFIG_WAIT_MS);
+	}
+
 	err = dw_pcie_host_init(pp);
 	if (err) {
 		dev_err(dev, "Failed to initialize host, err=%d\n", err);
@@ -444,6 +475,7 @@ 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 +486,24 @@ static int amd_mdb_pcie_probe(struct platform_device *pdev)
 
 	platform_set_drvdata(pdev, pcie);
 
+	ret = amd_mdb_parse_pcie_port(pcie);
+	/*
+	 * If amd_mdb_parse_pcie_port returns -ENODEV, it indicates that the
+	 * PCIe Bridge node was not found in the device tree. This is not
+	 * considered a fatal error and will trigger a fallback where the
+	 * reset GPIO is acquired directly from the PCIe Host Bridge node.
+	 */
+	if (ret) {
+		if (ret != -ENODEV)
+			return ret;
+
+		pcie->perst_gpio = devm_gpiod_get_optional(dev, "reset",
+							   GPIOD_OUT_HIGH);
+		if (IS_ERR(pcie->perst_gpio))
+			return dev_err_probe(dev, PTR_ERR(pcie->perst_gpio),
+					     "Failed to request reset GPIO\n");
+	}
+
 	return amd_mdb_add_pcie_port(pcie, pdev);
 }
 
-- 
2.43.0