[PATCH v6 1/2] PCI: Add a helper to check Power Resource Requirements _PR3 existence

[Kai-Heng Feng <kai.heng.feng@canonical.com>]

A driver may want to know the existence of _PR3, to choose different
runtime suspend behavior. A user will be add in next patch.

This is mostly the same as nouveau_pr3_present().

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
---
v6:
- Only define the function when CONFIG_ACPI is set.
v5:
- Add wording suggestion from Bjorn.
v4:
- Let caller to find its upstream port device.

 drivers/pci/pci.c   | 18 ++++++++++++++++++
 include/linux/pci.h |  2 ++
 2 files changed, 20 insertions(+)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index e7982af9a5d8..1df99d9e350e 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5856,6 +5856,24 @@ int pci_set_vga_state(struct pci_dev *dev, bool decode,
 	return 0;
 }
 
+#ifdef CONFIG_ACPI
+bool pci_pr3_present(struct pci_dev *pdev)
+{
+	struct acpi_device *adev;
+
+	if (acpi_disabled)
+		return false;
+
+	adev = ACPI_COMPANION(&pdev->dev);
+	if (!adev)
+		return false;
+
+	return adev->power.flags.power_resources &&
+		acpi_has_method(adev->handle, "_PR3");
+}
+EXPORT_SYMBOL_GPL(pci_pr3_present);
+#endif
+
 /**
  * pci_add_dma_alias - Add a DMA devfn alias for a device
  * @dev: the PCI device for which alias is added
diff --git a/include/linux/pci.h b/include/linux/pci.h
index f9088c89a534..1d15c5d49cdd 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -2310,9 +2310,11 @@ struct irq_domain *pci_host_bridge_acpi_msi_domain(struct pci_bus *bus);
 
 void
 pci_msi_register_fwnode_provider(struct fwnode_handle *(*fn)(struct device *));
+bool pci_pr3_present(struct pci_dev *pdev);
 #else
 static inline struct irq_domain *
 pci_host_bridge_acpi_msi_domain(struct pci_bus *bus) { return NULL; }
+static bool pci_pr3_present(struct pci_dev *pdev) { return false; }
 #endif
 
 #ifdef CONFIG_EEH
-- 
2.17.1