[PATCH v2 1/2] PCI: Add support for a functional level reset based on _RST method

[Shanker Donthineni <sdonthineni@nvidia.com>]

The _RST is a standard method specified in the ACPI specification. It
provides a function level reset when it is described in the acpi_device
context associated with PCI-device.

Implement a new reset function pci_dev_acpi_reset() for probing RST
method and execute if it is defined in the firmware.

The ACPI based reset is called after the device-specific reset and
before standard PCI hardware resets.

Signed-off-by: Shanker Donthineni <sdonthineni@nvidia.com>
---
 drivers/pci/pci.c | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 16a17215f633..6dadb19848c2 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5054,6 +5054,35 @@ static void pci_dev_restore(struct pci_dev *dev)
 		err_handler->reset_done(dev);
 }
 
+/**
+ * pci_dev_acpi_reset - do a function level reset using _RST method
+ * @dev: device to reset
+ * @probe: check if _RST method is included in the acpi_device context.
+ */
+static int pci_dev_acpi_reset(struct pci_dev *dev, int probe)
+{
+#ifdef CONFIG_ACPI
+	acpi_handle handle = ACPI_HANDLE(&dev->dev);
+
+	/* Return -ENOTTY if _RST method is not included in the dev context */
+	if (!handle || !acpi_has_method(handle, "_RST"))
+		return -ENOTTY;
+
+	/* Return 0 for probe phase indicating that we can reset this device */
+	if (probe)
+		return 0;
+
+	/* Invoke _RST() method to perform a function level reset */
+	if (ACPI_FAILURE(acpi_evaluate_object(handle, "_RST", NULL, NULL))) {
+		pci_warn(dev, "Failed to reset the device\n");
+		return -EINVAL;
+	}
+	return 0;
+#else
+	return -ENOTTY;
+#endif
+}
+
 /**
  * __pci_reset_function_locked - reset a PCI device function while holding
  * the @dev mutex lock.
@@ -5089,6 +5118,9 @@ int __pci_reset_function_locked(struct pci_dev *dev)
 	 * reset mechanisms might be broken on the device.
 	 */
 	rc = pci_dev_specific_reset(dev, 0);
+	if (rc != -ENOTTY)
+		return rc;
+	rc = pci_dev_acpi_reset(dev, 0);
 	if (rc != -ENOTTY)
 		return rc;
 	if (pcie_has_flr(dev)) {
@@ -5127,6 +5159,9 @@ int pci_probe_reset_function(struct pci_dev *dev)
 	might_sleep();
 
 	rc = pci_dev_specific_reset(dev, 1);
+	if (rc != -ENOTTY)
+		return rc;
+	rc = pci_dev_acpi_reset(dev, 1);
 	if (rc != -ENOTTY)
 		return rc;
 	if (pcie_has_flr(dev))
-- 
2.17.1