[PATCH 1/3] PCI: host-common: Add shared D3cold eligibility helper for host bridges

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

Add a common helper, pci_host_common_can_enter_d3cold(), to determine
whether a PCI host bridge can safely transition to D3cold.

The helper walks all devices on the bridge's bus and only allows the
host bridge to enter D3cold if all PCIe endpoints are already in
PCI_D3hot. For devices that may wake the system, it additionally
requires that the device supports PME wakeup from D3cold(with WAKE#).
Devices without wakeup enabled are not restricted by this check and can
be allowed to keep device in D3cold.

Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
---
 drivers/pci/controller/pci-host-common.c | 29 +++++++++++++++++++++++++++++
 drivers/pci/controller/pci-host-common.h |  2 ++
 2 files changed, 31 insertions(+)

diff --git a/drivers/pci/controller/pci-host-common.c b/drivers/pci/controller/pci-host-common.c
index c473e7c03bacad2de07c798768f99652443431e0..225472c5ac82c6c5b44257d68a0fc503ec046ff1 100644
--- a/drivers/pci/controller/pci-host-common.c
+++ b/drivers/pci/controller/pci-host-common.c
@@ -106,5 +106,34 @@ void pci_host_common_remove(struct platform_device *pdev)
 }
 EXPORT_SYMBOL_GPL(pci_host_common_remove);
 
+static int pci_host_common_check_d3cold(struct pci_dev *pdev, void *userdata)
+{
+	bool *d3cold_allow = userdata;
+
+	if (pci_pcie_type(pdev) != PCI_EXP_TYPE_ENDPOINT)
+		return 0;
+
+	if (pdev->current_state != PCI_D3hot)
+		goto exit;
+
+	if (device_may_wakeup(&pdev->dev) && !pci_pme_capable(pdev, PCI_D3cold))
+		goto exit;
+
+	return 0;
+exit:
+	*d3cold_allow = false;
+	return -EBUSY;
+}
+
+bool pci_host_common_can_enter_d3cold(struct pci_host_bridge *bridge)
+{
+	bool d3cold_allow = true;
+
+	pci_walk_bus(bridge->bus, pci_host_common_check_d3cold, &d3cold_allow);
+
+	return d3cold_allow;
+}
+EXPORT_SYMBOL_GPL(pci_host_common_can_enter_d3cold);
+
 MODULE_DESCRIPTION("Common library for PCI host controller drivers");
 MODULE_LICENSE("GPL v2");
diff --git a/drivers/pci/controller/pci-host-common.h b/drivers/pci/controller/pci-host-common.h
index b5075d4bd7eb31fbf1dc946ef1a6afd5afb5b3c6..18a731bca058828340bca84776d0e91da1edbbf7 100644
--- a/drivers/pci/controller/pci-host-common.h
+++ b/drivers/pci/controller/pci-host-common.h
@@ -20,4 +20,6 @@ void pci_host_common_remove(struct platform_device *pdev);
 
 struct pci_config_window *pci_host_common_ecam_create(struct device *dev,
 	struct pci_host_bridge *bridge, const struct pci_ecam_ops *ops);
+
+bool pci_host_common_can_enter_d3cold(struct pci_host_bridge *bridge);
 #endif

-- 
2.34.1