[PATCH v4 1/2] PCI: Add support for a function level reset based on _RST method

[Shanker Donthineni]

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 binding
information is available only after calling device_add(), so move
pci_init_reset_methods() to end of the pci_device_add().

The default priority of the acpi reset is set to below device-specific
and above hardware resets.

Signed-off-by: Shanker Donthineni <sdonthineni@xxxxxxxxxx>
---
changes since v2:
 - fix typo in the commit text
changes since v2:
 - rebase patch on top of https://lore.kernel.org/linux-pci/20210409192324.30080-1-ameynarkhede03@xxxxxxxxx/

 drivers/pci/pci.c   | 30 ++++++++++++++++++++++++++++++
 drivers/pci/probe.c |  2 +-
 include/linux/pci.h |  2 +-
 3 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 664cf2d358d6..510f9224a3b0 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5076,6 +5076,35 @@ 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
+}
+
 /*
  * The ordering for functions in pci_reset_fn_methods
  * is required for reset_methods byte array defined
@@ -5083,6 +5112,7 @@ static void pci_dev_restore(struct pci_dev *dev)
  */
 const struct pci_reset_fn_method pci_reset_fn_methods[] = {
 	{ .reset_fn = &pci_dev_specific_reset, .name = "device_specific" },
+	{ .reset_fn = &pci_dev_acpi_reset, .name = "acpi_reset" },
 	{ .reset_fn = &pcie_reset_flr, .name = "flr" },
 	{ .reset_fn = &pci_af_flr, .name = "af_flr" },
 	{ .reset_fn = &pci_pm_reset, .name = "pm" },
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 4764e031a44b..d4becd6ffb52 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2403,7 +2403,6 @@ static void pci_init_capabilities(struct pci_dev *dev)
 	pci_rcec_init(dev);		/* Root Complex Event Collector */
 
 	pcie_report_downtraining(dev);
-	pci_init_reset_methods(dev);
 }
 
 /*
@@ -2494,6 +2493,7 @@ void pci_device_add(struct pci_dev *dev, struct pci_bus *bus)
 	dev->match_driver = false;
 	ret = device_add(&dev->dev);
 	WARN_ON(ret < 0);
+	pci_init_reset_methods(dev);
 }
 
 struct pci_dev *pci_scan_single_device(struct pci_bus *bus, int devfn)
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 9f8347799634..b4a5d2146542 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -49,7 +49,7 @@
 			       PCI_STATUS_SIG_TARGET_ABORT | \
 			       PCI_STATUS_PARITY)
 
-#define PCI_RESET_FN_METHODS 5
+#define PCI_RESET_FN_METHODS 6
 
 /*
  * The PCI interface treats multi-function devices as independent
-- 
2.17.1