PCI/ACPI: Optimize device state transition delays

The PCI "ACPI additions for FW latency optimizations" ECN (link below)
defines two functions in the PCI _DSM:

  Function 8, "Reset Delay," applies to the entire hierarchy below a PCI
  host bridge.  If it returns one, the OS may assume that all devices in
  the hierarchy have already completed power-on reset delays.

  Function 9, "Device Readiness Durations," applies only to the object
  where it is located.  It returns delay durations required after various
  events if the device requires less time than the spec requires.  Delays
  from this function take precedence over the Reset Delay function.

Add support for Reset Delay and part of Device Readiness Durations.

[bhelgaas: changelog, comments]
Link: https://www.pcisig.com/specifications/conventional/pci_firmware/ECN_fw_latency_optimization_final.pdf
Signed-off-by: Aaron Lu <aaron.lu@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

3 files changed, 77 insertions, 0 deletions

diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
index bea6be4992c3..5eba74716900 100644
--- a/drivers/pci/pci-acpi.c
+++ b/drivers/pci/pci-acpi.c
@@ -537,11 +537,32 @@ static struct pci_platform_pm_ops acpi_pci_platform_pm = {
 
 void acpi_pci_add_bus(struct pci_bus *bus)
 {
+	union acpi_object *obj;
+	struct pci_host_bridge *bridge;
+
 	if (acpi_pci_disabled || !bus->bridge)
 		return;
 
 	acpi_pci_slot_enumerate(bus);
 	acpiphp_enumerate_slots(bus);
+
+	/*
+	 * For a host bridge, check its _DSM for function 8 and if
+	 * that is available, mark it in pci_host_bridge.
+	 */
+	if (!pci_is_root_bus(bus))
+		return;
+
+	obj = acpi_evaluate_dsm(ACPI_HANDLE(bus->bridge), pci_acpi_dsm_uuid, 3,
+				RESET_DELAY_DSM, NULL);
+	if (!obj)
+		return;
+
+	if (obj->type == ACPI_TYPE_INTEGER && obj->integer.value == 1) {
+		bridge = pci_find_host_bridge(bus);
+		bridge->ignore_reset_delay = 1;
+	}
+	ACPI_FREE(obj);
 }
 
 void acpi_pci_remove_bus(struct pci_bus *bus)
@@ -567,6 +588,57 @@ static struct acpi_device *acpi_pci_find_companion(struct device *dev)
 				      check_children);
 }
 
+/**
+ * pci_acpi_optimize_delay - optimize PCI D3 and D3cold delay from ACPI
+ * @pdev: the PCI device whose delay is to be updated
+ * @adev: the companion ACPI device of this PCI device
+ *
+ * Update the d3_delay and d3cold_delay of a PCI device from the ACPI _DSM
+ * control method of either the device itself or the PCI host bridge.
+ *
+ * Function 8, "Reset Delay," applies to the entire hierarchy below a PCI
+ * host bridge.  If it returns one, the OS may assume that all devices in
+ * the hierarchy have already completed power-on reset delays.
+ *
+ * Function 9, "Device Readiness Durations," applies only to the object
+ * where it is located.  It returns delay durations required after various
+ * events if the device requires less time than the spec requires.  Delays
+ * from this function take precedence over the Reset Delay function.
+ *
+ * These _DSM functions are defined by the draft ECN of January 28, 2014,
+ * titled "ACPI additions for FW latency optimizations."
+ */
+static void pci_acpi_optimize_delay(struct pci_dev *pdev,
+				    acpi_handle handle)
+{
+	struct pci_host_bridge *bridge = pci_find_host_bridge(pdev->bus);
+	int value;
+	union acpi_object *obj, *elements;
+
+	if (bridge->ignore_reset_delay)
+		pdev->d3cold_delay = 0;
+
+	obj = acpi_evaluate_dsm(handle, pci_acpi_dsm_uuid, 3,
+				FUNCTION_DELAY_DSM, NULL);
+	if (!obj)
+		return;
+
+	if (obj->type == ACPI_TYPE_PACKAGE && obj->package.count == 5) {
+		elements = obj->package.elements;
+		if (elements[0].type == ACPI_TYPE_INTEGER) {
+			value = (int)elements[0].integer.value / 1000;
+			if (value < PCI_PM_D3COLD_WAIT)
+				pdev->d3cold_delay = value;
+		}
+		if (elements[3].type == ACPI_TYPE_INTEGER) {
+			value = (int)elements[3].integer.value / 1000;
+			if (value < PCI_PM_D3_WAIT)
+				pdev->d3_delay = value;
+		}
+	}
+	ACPI_FREE(obj);
+}
+
 static void pci_acpi_setup(struct device *dev)
 {
 	struct pci_dev *pci_dev = to_pci_dev(dev);
@@ -575,6 +647,8 @@ static void pci_acpi_setup(struct device *dev)
 	if (!adev)
 		return;
 
+	pci_acpi_optimize_delay(pci_dev, adev->handle);
+
 	pci_acpi_add_pm_notifier(adev, pci_dev);
 	if (!adev->wakeup.flags.valid)
 		return;
diff --git a/include/linux/pci-acpi.h b/include/linux/pci-acpi.h
index 3801c704a945..a965efa52152 100644
--- a/include/linux/pci-acpi.h
+++ b/include/linux/pci-acpi.h
@@ -79,6 +79,8 @@ static inline void acpiphp_check_host_bridge(struct acpi_device *adev) { }
 
 extern const u8 pci_acpi_dsm_uuid[];
 #define DEVICE_LABEL_DSM	0x07
+#define RESET_DELAY_DSM		0x08
+#define FUNCTION_DELAY_DSM	0x09
 
 #else	/* CONFIG_ACPI */
 static inline void acpi_pci_add_bus(struct pci_bus *bus) { }
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 211e9da8a7d7..c5aa7b8a40c1 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -406,6 +406,7 @@ struct pci_host_bridge {
 	struct list_head windows;	/* resource_entry */
 	void (*release_fn)(struct pci_host_bridge *);
 	void *release_data;
+	unsigned int ignore_reset_delay:1;	/* for entire hierarchy */
 };
 
 #define	to_pci_host_bridge(n) container_of(n, struct pci_host_bridge, dev)