Message-Id: <20250912-pci-pwrctrl-perst-v3-3-3c0ac62b032c@oss.qualcomm.com>
Date: Fri, 12 Sep 2025 14:05:03 +0530
From: Manivannan Sadhasivam via B4 Relay <devnull+manivannan.sadhasivam.oss.qualcomm.com@...nel.org>
To: Manivannan Sadhasivam <mani@...nel.org>, 
 Lorenzo Pieralisi <lpieralisi@...nel.org>, 
 Krzysztof Wilczyński <kwilczynski@...nel.org>, 
 Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>, 
 Bartosz Golaszewski <brgl@...ev.pl>, Saravana Kannan <saravanak@...gle.com>
Cc: linux-pci@...r.kernel.org, linux-arm-msm@...r.kernel.org, 
 linux-kernel@...r.kernel.org, devicetree@...r.kernel.org, 
 Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>, 
 Brian Norris <briannorris@...omium.org>, 
 Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>
Subject: [PATCH v3 3/4] PCI: qcom: Parse PERST# from all PCIe bridge nodes

From: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>

Devicetree schema allows the PERST# GPIO to be present in all PCIe bridge
nodes, not just in Root Port node. But the current logic parses PERST# only
from the Root Port nodes. Though it is not causing any issue on the current
platforms, the upcoming platforms will have PERST# in PCIe switch
downstream ports also. So this requires parsing all the PCIe bridge nodes
for the PERST# GPIO.

Hence, rework the parsing logic to extend to all PCIe bridge nodes starting
from the Root Port node. If the 'reset-gpios' property is found for a PCI
bridge node, the GPIO descriptor will be stored in qcom_pcie_perst::desc
and added to the qcom_pcie_port::perst list.

It should be noted that if more than one bridge node has the same GPIO for
PERST# (shared PERST#), the driver will error out. This is due to the
limitation in the GPIOLIB subsystem that allows only exclusive (non-shared)
access to GPIOs from consumers. But this is soon going to get fixed. Once
that happens, it will get incorporated in this driver.

So for now, PERST# sharing is not supported.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>
---
 drivers/pci/controller/dwc/pcie-qcom.c | 102 +++++++++++++++++++++++++++------
 1 file changed, 85 insertions(+), 17 deletions(-)

diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
index 6170c86f465f43f980f5b2f88bd8799c3c152e68..ccff01c31898cdbc5634221e7f8ef7e86469f5fd 100644
--- a/drivers/pci/controller/dwc/pcie-qcom.c
+++ b/drivers/pci/controller/dwc/pcie-qcom.c
@@ -267,10 +267,15 @@ struct qcom_pcie_cfg {
 	bool no_l0s;
 };
 
+struct qcom_pcie_perst {
+	struct list_head list;
+	struct gpio_desc *desc;
+};
+
 struct qcom_pcie_port {
 	struct list_head list;
-	struct gpio_desc *reset;
 	struct phy *phy;
+	struct list_head perst;
 };
 
 struct qcom_pcie {
@@ -292,11 +297,14 @@ struct qcom_pcie {
 
 static void qcom_perst_assert(struct qcom_pcie *pcie, bool assert)
 {
+	struct qcom_pcie_perst *perst;
 	struct qcom_pcie_port *port;
 	int val = assert ? 1 : 0;
 
-	list_for_each_entry(port, &pcie->ports, list)
-		gpiod_set_value_cansleep(port->reset, val);
+	list_for_each_entry(port, &pcie->ports, list) {
+		list_for_each_entry(perst, &port->perst, list)
+			gpiod_set_value_cansleep(perst->desc, val);
+	}
 
 	usleep_range(PERST_DELAY_US, PERST_DELAY_US + 500);
 }
@@ -1670,18 +1678,58 @@ static const struct pci_ecam_ops pci_qcom_ecam_ops = {
 	}
 };
 
-static int qcom_pcie_parse_port(struct qcom_pcie *pcie, struct device_node *node)
+/* Parse PERST# from all nodes in depth first manner starting from @np */
+static int qcom_pcie_parse_perst(struct qcom_pcie *pcie,
+				 struct qcom_pcie_port *port,
+				 struct device_node *np)
 {
 	struct device *dev = pcie->pci->dev;
-	struct qcom_pcie_port *port;
+	struct qcom_pcie_perst *perst;
 	struct gpio_desc *reset;
-	struct phy *phy;
 	int ret;
 
-	reset = devm_fwnode_gpiod_get(dev, of_fwnode_handle(node),
-				      "reset", GPIOD_OUT_HIGH, "PERST#");
-	if (IS_ERR(reset))
+	if (!of_find_property(np, "reset-gpios", NULL))
+		goto parse_child_node;
+
+	reset = devm_fwnode_gpiod_get(dev, of_fwnode_handle(np), "reset",
+				      GPIOD_OUT_HIGH, "PERST#");
+	if (IS_ERR(reset)) {
+		/*
+		 * FIXME: GPIOLIB currently supports exclusive GPIO access only.
+		 * Non exclusive access is broken. But shared PERST# requires
+		 * non-exclusive access. So once GPIOLIB properly supports it,
+		 * implement it here.
+		 */
+		if (PTR_ERR(reset) == -EBUSY)
+			dev_err(dev, "Shared PERST# is not supported\n");
+
 		return PTR_ERR(reset);
+	}
+
+	perst = devm_kzalloc(dev, sizeof(*perst), GFP_KERNEL);
+	if (!perst)
+		return -ENOMEM;
+
+	INIT_LIST_HEAD(&perst->list);
+	perst->desc = reset;
+	list_add_tail(&perst->list, &port->perst);
+
+parse_child_node:
+	for_each_available_child_of_node_scoped(np, child) {
+		ret = qcom_pcie_parse_perst(pcie, port, child);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+static int qcom_pcie_parse_port(struct qcom_pcie *pcie, struct device_node *node)
+{
+	struct device *dev = pcie->pci->dev;
+	struct qcom_pcie_port *port;
+	struct phy *phy;
+	int ret;
 
 	phy = devm_of_phy_get(dev, node, NULL);
 	if (IS_ERR(phy))
@@ -1695,7 +1743,12 @@ static int qcom_pcie_parse_port(struct qcom_pcie *pcie, struct device_node *node
 	if (ret)
 		return ret;
 
-	port->reset = reset;
+	INIT_LIST_HEAD(&port->perst);
+
+	ret = qcom_pcie_parse_perst(pcie, port, node);
+	if (ret)
+		return ret;
+
 	port->phy = phy;
 	INIT_LIST_HEAD(&port->list);
 	list_add_tail(&port->list, &pcie->ports);
@@ -1705,9 +1758,10 @@ static int qcom_pcie_parse_port(struct qcom_pcie *pcie, struct device_node *node
 
 static int qcom_pcie_parse_ports(struct qcom_pcie *pcie)
 {
+	struct qcom_pcie_perst *perst, *tmp_perst;
+	struct qcom_pcie_port *port, *tmp_port;
 	struct device *dev = pcie->pci->dev;
-	struct qcom_pcie_port *port, *tmp;
-	int ret = -ENOENT;
+	int ret = -ENODEV;
 
 	for_each_available_child_of_node_scoped(dev->of_node, of_port) {
 		ret = qcom_pcie_parse_port(pcie, of_port);
@@ -1718,7 +1772,9 @@ static int qcom_pcie_parse_ports(struct qcom_pcie *pcie)
 	return ret;
 
 err_port_del:
-	list_for_each_entry_safe(port, tmp, &pcie->ports, list) {
+	list_for_each_entry_safe(port, tmp_port, &pcie->ports, list) {
+		list_for_each_entry_safe(perst, tmp_perst, &port->perst, list)
+			list_del(&perst->list);
 		phy_exit(port->phy);
 		list_del(&port->list);
 	}
@@ -1729,6 +1785,7 @@ static int qcom_pcie_parse_ports(struct qcom_pcie *pcie)
 static int qcom_pcie_parse_legacy_binding(struct qcom_pcie *pcie)
 {
 	struct device *dev = pcie->pci->dev;
+	struct qcom_pcie_perst *perst;
 	struct qcom_pcie_port *port;
 	struct gpio_desc *reset;
 	struct phy *phy;
@@ -1750,19 +1807,28 @@ static int qcom_pcie_parse_legacy_binding(struct qcom_pcie *pcie)
 	if (!port)
 		return -ENOMEM;
 
-	port->reset = reset;
+	perst = devm_kzalloc(dev, sizeof(*perst), GFP_KERNEL);
+	if (!perst)
+		return -ENOMEM;
+
 	port->phy = phy;
 	INIT_LIST_HEAD(&port->list);
 	list_add_tail(&port->list, &pcie->ports);
 
+	perst->desc = reset;
+	INIT_LIST_HEAD(&port->perst);
+	INIT_LIST_HEAD(&perst->list);
+	list_add_tail(&perst->list, &port->perst);
+
 	return 0;
 }
 
 static int qcom_pcie_probe(struct platform_device *pdev)
 {
+	struct qcom_pcie_perst *perst, *tmp_perst;
+	struct qcom_pcie_port *port, *tmp_port;
 	const struct qcom_pcie_cfg *pcie_cfg;
 	unsigned long max_freq = ULONG_MAX;
-	struct qcom_pcie_port *port, *tmp;
 	struct device *dev = &pdev->dev;
 	struct dev_pm_opp *opp;
 	struct qcom_pcie *pcie;
@@ -1909,7 +1975,7 @@ static int qcom_pcie_probe(struct platform_device *pdev)
 
 	ret = qcom_pcie_parse_ports(pcie);
 	if (ret) {
-		if (ret != -ENOENT) {
+		if (ret != -ENODEV) {
 			dev_err_probe(pci->dev, ret,
 				      "Failed to parse Root Port: %d\n", ret);
 			goto err_pm_runtime_put;
@@ -1968,7 +2034,9 @@ static int qcom_pcie_probe(struct platform_device *pdev)
 err_host_deinit:
 	dw_pcie_host_deinit(pp);
 err_phy_exit:
-	list_for_each_entry_safe(port, tmp, &pcie->ports, list) {
+	list_for_each_entry_safe(port, tmp_port, &pcie->ports, list) {
+		list_for_each_entry_safe(perst, tmp_perst, &port->perst, list)
+			list_del(&perst->list);
 		phy_exit(port->phy);
 		list_del(&port->list);
 	}

-- 
2.45.2

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