PCI: host-common: Add pci_host_common_d3cold_possible() helper

Add a common helper, pci_host_common_d3cold_possible(), to determine
whether PCIe devices under host bridge can safely transition to D3cold.

This helper is intended to be used by PCI host controller drivers to decide
whether they can safely put the endpoint devices into D3cold based on their
power state and wakeup capabilities. Once the devices are transitioned into
D3cold, the host controller can be safely powered off.

The helper walks all devices on the all downstream buses and only allows
the devices to enter D3cold if all PCIe endpoints are already in
PCI_D3hot. This ensures that the host controller driver does not broadcast
PME_Turn_Off or power down the controller while any active endpoint still
requires the link to remain powered.

For devices that may wake the system, the helper additionally requires that
the device supports PME wake from D3cold (via WAKE#). Devices that do not
have wakeup enabled are not restricted by this check and do not block the
devices under host bridge from entering D3cold.

Devices without a bound driver and with PCI not enabled via sysfs are
treated as inactive and therefore do not prevent the devices under host
bridge from entering D3cold. This allows controllers to power down more
aggressively when there are no actively managed endpoints.

Some devices (e.g. M.2 without auxiliary power) lose PME detection when
main power is removed. Even if such devices advertise PME-from-D3cold
capability, entering D3cold may break wakeup. Return PME-from-D3cold
capability via 'pme_capable' parameter so PCIe controller drivers can apply
platform-specific handling to preserve wakeup functionality.

Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
[mani: commit log and removed the device checks for d3cold]
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://patch.msgid.link/20260429-d3cold-v5-1-89e9735b9df6@oss.qualcomm.com

diff --git a/drivers/pci/controller/pci-host-common.c b/drivers/pci/controller/pci-host-common.c
index d6258c1cffe5ec480fd2a7e50b3af39ef6ac4c8c..2e785449d02cb0f89894493128105722a31b9fe6 100644 (file)
--- a/drivers/pci/controller/pci-host-common.c
+++ b/drivers/pci/controller/pci-host-common.c
@@ -17,6 +17,9 @@
 
 #include "pci-host-common.h"
 
+#define PCI_HOST_D3COLD_ALLOWED        BIT(0)
+#define PCI_HOST_PME_D3COLD_CAPABLE    BIT(1)
+
 static void gen_pci_unmap_cfg(void *ptr)
 {
        pci_ecam_free((struct pci_config_window *)ptr);
@@ -106,5 +109,64 @@ void pci_host_common_remove(struct platform_device *pdev)
 }
 EXPORT_SYMBOL_GPL(pci_host_common_remove);
 
+static int __pci_host_common_d3cold_possible(struct pci_dev *pdev,
+                                            void *userdata)
+{
+       u32 *flags = userdata;
+
+       if (!pdev->dev.driver && !pci_is_enabled(pdev))
+               return 0;
+
+       if (pdev->current_state != PCI_D3hot)
+               goto exit;
+
+       if (device_may_wakeup(&pdev->dev)) {
+               if (!pci_pme_capable(pdev, PCI_D3cold))
+                       goto exit;
+               else
+                       *flags |= PCI_HOST_PME_D3COLD_CAPABLE;
+       }
+
+       return 0;
+
+exit:
+       *flags &= ~PCI_HOST_D3COLD_ALLOWED;
+
+       return -EOPNOTSUPP;
+}
+
+/**
+ * pci_host_common_d3cold_possible - Determine whether the host bridge can
+ *                                  transition the devices into D3cold.
+ *
+ * @bridge: PCI host bridge to check
+ * @pme_capable: Pointer to update if there is any device capable of generating
+ *              PME from D3cold.
+ *
+ * Walk downstream PCIe endpoint devices and determine whether the host bridge
+ * is permitted to transition the devices into D3cold.
+ *
+ * Devices under host bridge can enter D3cold only if all active PCIe
+ * endpoints are in PCI_D3hot and any wakeup-enabled endpoint is capable of
+ * generating PME from D3cold.  Inactive endpoints are ignored.
+ *
+ * The @pme_capable output allows PCIe controller drivers to apply
+ * platform-specific handling to preserve wakeup functionality.
+ *
+ * Return: %true if the host bridge may enter D3cold, otherwise %false.
+ */
+bool pci_host_common_d3cold_possible(struct pci_host_bridge *bridge,
+                                    bool *pme_capable)
+{
+       u32 flags = PCI_HOST_D3COLD_ALLOWED;
+
+       pci_walk_bus(bridge->bus, __pci_host_common_d3cold_possible, &flags);
+
+       *pme_capable = !!(flags & PCI_HOST_PME_D3COLD_CAPABLE);
+
+       return !!(flags & PCI_HOST_D3COLD_ALLOWED);
+}
+EXPORT_SYMBOL_GPL(pci_host_common_d3cold_possible);
+
 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..1649858782659be4169022a2599863263f774596 100644 (file)
--- a/drivers/pci/controller/pci-host-common.h
+++ b/drivers/pci/controller/pci-host-common.h
@@ -20,4 +20,7 @@ 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_d3cold_possible(struct pci_host_bridge *bridge,
+                                    bool *pme_capable);
 #endif