[PATCH v4 3/3] PCI: Add support for PCIe WAKE# interrupt

[Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>]

According to the PCIe specification 6, sec 5.3.3.2, there are two defined
wakeup mechanisms: Beacon and WAKE# for the Link wakeup mechanisms to
provide a means of signaling the platform to re-establish power and
reference clocks to the components within its domain. Adding WAKE#
support in PCI framework.

According to the PCIe specification, multiple WAKE# signals can exist in a
system. In configurations involving a PCIe switch, each downstream port
(DSP) of the switch may be connected to a separate WAKE# line, allowing
each endpoint to signal WAKE# independently. To support this, the WAKE#
should be described in the device tree node of the upstream bridge to which
the endpoint is connected. For example, in a switch-based topology, the
WAKE# can be defined in the DSP of the switch. In a direct connection
scenario, the WAKE# can be defined in the root port. If all endpoints share
a single WAKE# line, the GPIO should be defined in the root port.

During endpoint probe, the driver searches for the WAKE# in its immediate
upstream bridge. If not found, it continues walking up the hierarchy until
it either finds a WAKE# or reaches the root port. Once found, the driver
registers the wake IRQ in shared mode, as the WAKE# may be shared among
multiple endpoints.

When the IRQ is asserted, the wake handler triggers a pm_runtime_resume().
The PM framework ensures that the parent device is resumed before the
child i.e controller driver which can bring back link to D0.

WAKE# is added in dts schema and merged based on this link.

Link: https://lore.kernel.org/all/20250515090517.3506772-1-krishna.chundru@oss.qualcomm.com/
Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
---
 drivers/pci/of.c         | 66 ++++++++++++++++++++++++++++++++++++++++++++++++
 drivers/pci/pci-driver.c | 10 ++++++++
 drivers/pci/pci.h        | 10 ++++++++
 drivers/pci/probe.c      |  2 ++
 drivers/pci/remove.c     |  1 +
 include/linux/pci.h      |  2 ++
 6 files changed, 91 insertions(+)

diff --git a/drivers/pci/of.c b/drivers/pci/of.c
index 3579265f119845637e163d9051437c89662762f8..5a832bbf2dd5da728080f83220f47c3578cb6b5a 100644
--- a/drivers/pci/of.c
+++ b/drivers/pci/of.c
@@ -7,6 +7,7 @@
 #define pr_fmt(fmt)	"PCI: OF: " fmt
 
 #include <linux/cleanup.h>
+#include <linux/gpio/consumer.h>
 #include <linux/irqdomain.h>
 #include <linux/kernel.h>
 #include <linux/pci.h>
@@ -15,6 +16,7 @@
 #include <linux/of_address.h>
 #include <linux/of_pci.h>
 #include <linux/platform_device.h>
+#include <linux/pm_wakeirq.h>
 #include "pci.h"
 
 #ifdef CONFIG_PCI
@@ -586,6 +588,29 @@ int of_irq_parse_and_map_pci(const struct pci_dev *dev, u8 slot, u8 pin)
 	return irq_create_of_mapping(&oirq);
 }
 EXPORT_SYMBOL_GPL(of_irq_parse_and_map_pci);
+
+void pci_parse_of_wake_gpio(struct pci_dev *dev)
+{
+	struct device_node *dn __free(device_node) = pci_device_to_OF_node(dev);
+	struct gpio_desc *gpio;
+
+	if (!dn)
+		return;
+
+	gpio = fwnode_gpiod_get_index(of_fwnode_handle(no_free_ptr(dn)),
+				      "wake", 0, GPIOD_IN, NULL);
+	if (!IS_ERR(gpio))
+		dev->wake = gpio;
+}
+
+void pci_remove_of_wake_gpio(struct pci_dev *dev)
+{
+	if (!dev->wake)
+		return;
+
+	gpiod_put(dev->wake);
+	dev->wake = NULL;
+}
 #endif	/* CONFIG_OF_IRQ */
 
 static int pci_parse_request_of_pci_ranges(struct device *dev,
@@ -1010,3 +1035,44 @@ int of_pci_get_equalization_presets(struct device *dev,
 	return 0;
 }
 EXPORT_SYMBOL_GPL(of_pci_get_equalization_presets);
+
+int pci_configure_wake_irq(struct pci_dev *pdev)
+{
+	struct pci_dev *bridge = pdev;
+	struct gpio_desc *wake;
+	int ret, wake_irq;
+
+	while (bridge) {
+		wake = bridge->wake;
+		if (wake)
+			break;
+		bridge = pci_upstream_bridge(bridge);  // Move to upstream bridge
+	}
+
+	if (!wake)
+		return 0;
+
+	wake_irq = gpiod_to_irq(wake);
+	if (wake_irq < 0) {
+		dev_err(&pdev->dev, "Failed to get wake irq: %d\n", wake_irq);
+		return wake_irq;
+	}
+
+	device_init_wakeup(&pdev->dev, true);
+
+	ret = dev_pm_set_dedicated_wake_irq_flags(&pdev->dev, wake_irq,
+						  IRQF_SHARED | IRQ_TYPE_EDGE_FALLING);
+	if (ret < 0) {
+		dev_err(&pdev->dev, "Failed to set wake IRQ: %d\n", ret);
+		device_init_wakeup(&pdev->dev, false);
+		return ret;
+	}
+
+	return 0;
+}
+
+void pci_remove_wake_irq(struct pci_dev *pdev)
+{
+	dev_pm_clear_wake_irq(&pdev->dev);
+	device_init_wakeup(&pdev->dev, false);
+}
diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
index b853585cb1f87216981bde2a7782b8ed9c337636..2a1dca1d19b914d21b300ea78be0e0dce418cc88 100644
--- a/drivers/pci/pci-driver.c
+++ b/drivers/pci/pci-driver.c
@@ -447,10 +447,19 @@ static int pci_device_probe(struct device *dev)
 	if (error < 0)
 		return error;
 
+	if (pci_pcie_type(pci_dev) == PCI_EXP_TYPE_ENDPOINT) {
+		error =  pci_configure_wake_irq(pci_dev);
+		if (error) {
+			pcibios_free_irq(pci_dev);
+			return error;
+		}
+	}
+
 	pci_dev_get(pci_dev);
 	error = __pci_device_probe(drv, pci_dev);
 	if (error) {
 		pcibios_free_irq(pci_dev);
+		pci_remove_wake_irq(pci_dev);
 		pci_dev_put(pci_dev);
 	}
 
@@ -475,6 +484,7 @@ static void pci_device_remove(struct device *dev)
 		pm_runtime_put_noidle(dev);
 	}
 	pcibios_free_irq(pci_dev);
+	pci_remove_wake_irq(pci_dev);
 	pci_dev->driver = NULL;
 	pci_iov_remove(pci_dev);
 
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 12215ee72afb682b669c0e3a582b5379828e70c4..c8cf0b404a4f31b271f187dddd75a007c7566982 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -920,6 +920,11 @@ void pci_release_of_node(struct pci_dev *dev);
 void pci_set_bus_of_node(struct pci_bus *bus);
 void pci_release_bus_of_node(struct pci_bus *bus);
 
+void pci_parse_of_wake_gpio(struct pci_dev *dev);
+void pci_remove_of_wake_gpio(struct pci_dev *dev);
+int pci_configure_wake_irq(struct pci_dev *pdev);
+void pci_remove_wake_irq(struct pci_dev *pdev);
+
 int devm_of_pci_bridge_init(struct device *dev, struct pci_host_bridge *bridge);
 bool of_pci_supply_present(struct device_node *np);
 int of_pci_get_equalization_presets(struct device *dev,
@@ -965,6 +970,11 @@ static inline int devm_of_pci_bridge_init(struct device *dev, struct pci_host_br
 	return 0;
 }
 
+static inline void pci_parse_of_wake_gpio(struct pci_dev *dev) { }
+static inline void pci_remove_of_wake_gpio(struct pci_dev *dev) { }
+static inline int pci_configure_wake_irq(struct pci_dev *pdev) { return 0; }
+static inline void pci_remove_wake_irq(struct pci_dev *pdev) { }
+
 static inline bool of_pci_supply_present(struct device_node *np)
 {
 	return false;
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index e6a34db778266862564532becc2a30aec09bab22..4fb9d8df19bc41cb84dcd1886546076bcc867a43 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2717,6 +2717,8 @@ void pci_device_add(struct pci_dev *dev, struct pci_bus *bus)
 	/* Set up MSI IRQ domain */
 	pci_set_msi_domain(dev);
 
+	pci_parse_of_wake_gpio(dev);
+
 	/* Notifier could use PCI capabilities */
 	ret = device_add(&dev->dev);
 	WARN_ON(ret < 0);
diff --git a/drivers/pci/remove.c b/drivers/pci/remove.c
index 445afdfa6498edc88f1ef89df279af1419025495..1910f7c18b8f9b11c8136fea970788aaf834c97f 100644
--- a/drivers/pci/remove.c
+++ b/drivers/pci/remove.c
@@ -52,6 +52,7 @@ static void pci_destroy_dev(struct pci_dev *dev)
 	if (pci_dev_test_and_set_removed(dev))
 		return;
 
+	pci_remove_of_wake_gpio(dev);
 	pci_doe_sysfs_teardown(dev);
 	pci_npem_remove(dev);
 
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 05e68f35f39238f8b9ce08df97b384d1c1e89bbe..8f861298e41d2f0d2dd0fc3f5778fe0e77a93511 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -548,6 +548,8 @@ struct pci_dev {
 	/* These methods index pci_reset_fn_methods[] */
 	u8 reset_methods[PCI_NUM_RESET_METHODS]; /* In priority order */
 
+	struct gpio_desc *wake; /* Holds WAKE# gpio */
+
 #ifdef CONFIG_PCIE_TPH
 	u16		tph_cap;	/* TPH capability offset */
 	u8		tph_mode;	/* TPH mode */

-- 
2.34.1