linux-kernel - [PATCH v1 3/3] PCI: ACPI: PM: Power up devices in D3cold before scanning them

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Date:   Mon, 04 Apr 2022 17:25:04 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Linux ACPI <linux-acpi@...r.kernel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>
Subject: [PATCH v1 3/3] PCI: ACPI: PM: Power up devices in D3cold before scanning them

From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

The initial configuration of ACPI power resources on some systems
implies that some PCI devices on them are initially in D3cold.

In some cases, especially for PCIe Root Ports, this is a "logical"
D3cold, meaning that the configuration space of the device is
accessible, but some of its functionality may be missing, but it
very well may be real D3cold, in which case the device will not
be accessible at all.  However, the PCI bus type driver will need
to access its configuration space in order to enumerate it.

To prevent possible device enumeration failures that may ensue as
a result of ACPI power resources being initially in the "off"
state, power up all children of the host bridge ACPI device object
that hold valid _ADR objects (which indicates that they will be
enumerated by the PCI bus type driver) and do that to all children
of the ACPI device objects corresponding to PCI bridges (including
PCIe ports).

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 drivers/acpi/pci_root.c |    2 ++
 drivers/pci/pci-acpi.c  |    3 +++
 2 files changed, 5 insertions(+)

Index: linux-pm/drivers/acpi/pci_root.c
===================================================================
--- linux-pm.orig/drivers/acpi/pci_root.c
+++ linux-pm/drivers/acpi/pci_root.c
@@ -927,6 +927,8 @@ struct pci_bus *acpi_pci_root_create(str
 		host_bridge->preserve_config = 1;
 	ACPI_FREE(obj);

+	acpi_dev_power_up_children_with_adr(device);
+
 	pci_scan_child_bus(bus);
 	pci_set_host_bridge_release(host_bridge, acpi_pci_root_release_info,
 				    info);
Index: linux-pm/drivers/pci/pci-acpi.c
===================================================================
--- linux-pm.orig/drivers/pci/pci-acpi.c
+++ linux-pm/drivers/pci/pci-acpi.c
@@ -1374,6 +1374,9 @@ void pci_acpi_setup(struct device *dev,

 	acpi_pci_wakeup(pci_dev, false);
 	acpi_device_power_add_dependent(adev, dev);
+
+	if (pci_is_bridge(pci_dev))
+		acpi_dev_power_up_children_with_adr(adev);
 }

 void pci_acpi_cleanup(struct device *dev, struct acpi_device *adev)