PCI/ACPI: Allow D3 only if Root Port can signal and wake from D3

acpi_pci_bridge_d3(dev) returns "true" if "dev" is a hotplug bridge that
can handle hotplug events while in D3. Previously this meant either:

- "dev" has a _PS0 or _PR0 method (acpi_pci_power_manageable()), or

- The Root Port above "dev" has a _DSD with a "HotPlugSupportInD3"
property with value 1.

This did not consider _PRW, which tells us about wakeup GPEs (ACPI v6.4,
sec 7.3.13). Without a wakeup GPE, from an ACPI perspective the Root Port
has no way of generating wakeup signals, so hotplug events will be lost if
we use D3.

Similarly, it did not consider _S0W, which tells us the deepest D-state
from which a device can wake itself (sec 7.3.20). If _S0W tells us the
device cannot wake from D3, hotplug events will again be lost if we use D3.

Some platforms, e.g., AMD Yellow Carp, supply "HotPlugSupportInD3" without
_PRW or with an _S0W that says the Root Port cannot wake from D3. On those
platforms, we previously put bridges in D3hot, hotplug events were lost,
and hotplugged devices would not be recognized without manually rescanning.

Allow bridges to be put in D3 only if the Root Port can generate wakeup
GPEs (wakeup.flags.valid), it can wake from D3 (_S0W), AND it has the
"HotPlugSupportInD3" property.

Neither Windows 10 nor Windows 11 puts the bridge in D3 when the firmware
is configured this way, and this change aligns the handling of the
situation to be the same.

[bhelgaas: commit log, tidy "HotPlugSupportInD3" check and comment]
Link: https://uefi.org/htmlspecs/ACPI_Spec_6_4_html/07_Power_and_Performance_Mgmt/device-power-management-objects.html?highlight=s0w#s0w-s0-device-wake-state
Link: https://docs.microsoft.com/en-us/windows-hardware/drivers/pci/dsd-for-pcie-root-ports#identifying-pcie-root-ports-supporting-hot-plug-in-d3
Link: https://lore.kernel.org/r/[e-mail]
Fixes: 26ad34d510a87 ("PCI / ACPI: Whitelist D3 for more PCIe hotplug ports")
Signed-off-by: Mario Limonciello <[e-mail]>
Signed-off-by: Bjorn Helgaas <[e-mail]>
Reviewed-by: Rafael J. Wysocki <[e-mail]>

drivers/pci/pci-acpi.c

···
 
 bool acpi_pci_bridge_d3(struct pci_dev *dev)
 {
-	const union acpi_object *obj;
-	struct acpi_device *adev;
 	struct pci_dev *rpdev;
+	struct acpi_device *adev;
+	acpi_status status;
+	unsigned long long state;
+	const union acpi_object *obj;
 
 	if (acpi_pci_disabled || !dev->is_hotplug_bridge)
 		return false;
···
 	if (acpi_pci_power_manageable(dev))
 		return true;
 
-	/*
-	 * The ACPI firmware will provide the device-specific properties through
-	 * _DSD configuration object. Look for the 'HotPlugSupportInD3' property
-	 * for the root port and if it is set we know the hierarchy behind it
-	 * supports D3 just fine.
-	 */
 	rpdev = pcie_find_root_port(dev);
 	if (!rpdev)
 		return false;
···
 	if (!adev)
 		return false;
 
-	if (acpi_dev_get_property(adev, "HotPlugSupportInD3",
-				   ACPI_TYPE_INTEGER, &obj) < 0)
+	/*
+	 * If the Root Port cannot signal wakeup signals at all, i.e., it
+	 * doesn't supply a wakeup GPE via _PRW, it cannot signal hotplug
+	 * events from low-power states including D3hot and D3cold.
+	 */
+	if (!adev->wakeup.flags.valid)
 		return false;
 
-	return obj->integer.value == 1;
+	/*
+	 * If the Root Port cannot wake itself from D3hot or D3cold, we
+	 * can't use D3.
+	 */
+	status = acpi_evaluate_integer(adev->handle, "_S0W", NULL, &state);
+	if (ACPI_SUCCESS(status) && state < ACPI_STATE_D3_HOT)
+		return false;
+
+	/*
+	 * The "HotPlugSupportInD3" property in a Root Port _DSD indicates
+	 * the Port can signal hotplug events while in D3.  We assume any
+	 * bridges *below* that Root Port can also signal hotplug events
+	 * while in D3.
+	 */
+	if (!acpi_dev_get_property(adev, "HotPlugSupportInD3",
+				   ACPI_TYPE_INTEGER, &obj) &&
+	    obj->integer.value == 1)
+		return true;
+
+	return false;
 }
 
 int acpi_pci_set_power_state(struct pci_dev *dev, pci_power_t state)