[PATCH] PCI / ACPI: PCI delay optimization from ACPI

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An ECN meant to specify possible delay optimizations is available on
the PCI website:
https://www.pcisig.com/specifications/conventional/pci_firmware/ECN_fw_latency_optimization_final.pdf
where it has defined two functions for an UUID specified _DSM:
Function 8: If system firmware assumes the responsibility of post
Conventional Reset delay (and informs the Operating System via this DSM
function) on Sx Resume (such as boot from ACPI S5, or resume from ACPI
S4 or S3 states), the Operating System may assume sufficient time has
elapsed since the end of reset, and devices within the PCI subsystem are
ready for Configuration Access.
If the system firmware supports runtime power gating on any of the
device within PCI subsystem covered by this DSM function, the system
firmware is responsible for covering the necessary post power-on reset
delay.

Function 9: Specify various smaller delay values than required by the
SPEC for individual PCI devices like shorter delay values after
conventional reset, D3hot to D0 transition, functional level reset, etc.

This patch adds support for function 8 and part of function 9. For
function 8, the patch will check if the required _DSM function satisfies
the requirement and then set the per PCI device's d3cold_delay variable
to zero. For function 9, the values affecting delays after conventional
reset and D3hot->D0 are examined and the per PCI device's d3cold_delay
and d3_delay are updated if the _DSM's return value is smaller than what
the SPEC requires.

Signed-off-by: Aaron Lu <aaron.lu@xxxxxxxxx>
---
 drivers/pci/pci-acpi.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 61 insertions(+)

diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
index 489063987325..c833b054c00c 100644
--- a/drivers/pci/pci-acpi.c
+++ b/drivers/pci/pci-acpi.c
@@ -558,6 +558,64 @@ static struct acpi_device *acpi_pci_find_companion(struct device *dev)
 				      check_children);
 }
 
+/**
+ * pci_acpi_delay_optimize - 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
+ *
+ * Description:
+ *   This function is used to update the d3_delay and d3cold_delay of a PCI
+ *   device from ACPI _DSM control method of either its own or its parent
+ *   bridge device. The UUID of the _DSM control method, together with other
+ *   information like which delay values can be optimized, etc. is defined in
+ *   the fw_latency_optimization ECN availabe on PCIsig.com.
+ *   Function 9 of the ACPI _DSM control method, if availabe for a specific PCI
+ *   device, provides various possible delay values that are less than what the
+ *   SPEC requires. Here, we only deal with d3_delay and d3cold_delay. Others
+ *   can be added later.
+ *   Function 8 of the ACPI _DSM control method, if availabe for a specific PCI
+ *   bridge, means all its children devices do not need the reset delay when
+ *   leaving from D3cold state.
+ */
+static void pci_acpi_delay_optimize(struct pci_dev *pdev, struct acpi_device *adev)
+{
+	const u8 uuid[] = {
+		0xd0, 0x37, 0xc9, 0xe5, 0x53, 0x35, 0x7a, 0x4d,
+		0x91, 0x17, 0xea, 0x4d, 0x19, 0xc3, 0x43, 0x4d
+	};
+	int revision = 3, function = 9, value;
+	acpi_handle handle = adev->handle;
+	union acpi_object *obj, *elements;
+
+	obj = acpi_evaluate_dsm(handle, uuid, revision, function, NULL);
+	if (obj) {
+		if (obj->type == ACPI_TYPE_PACKAGE && obj->package.count == 5) {
+			elements = obj->package.elements;
+			if (elements[3].type == ACPI_TYPE_INTEGER) {
+				value = (int)elements[3].integer.value / 1000;
+				if (value < PCI_PM_D3_WAIT)
+					pdev->d3_delay = value;
+			}
+			if (elements[0].type == ACPI_TYPE_INTEGER) {
+				value = (int)elements[0].integer.value / 1000;
+				if (value < PCI_PM_D3COLD_WAIT)
+					pdev->d3cold_delay = value;
+			}
+		}
+		kfree(obj);
+	}
+
+	function = 8;
+	handle = ACPI_HANDLE(pdev->bus->bridge);
+	obj = acpi_evaluate_dsm(handle, uuid, revision, function, NULL);
+	if (!obj)
+		return;
+
+	if (obj->type == ACPI_TYPE_INTEGER && obj->integer.value == 1)
+		pdev->d3cold_delay = 0;
+	kfree(obj);
+}
+
 static void pci_acpi_setup(struct device *dev)
 {
 	struct pci_dev *pci_dev = to_pci_dev(dev);
@@ -566,6 +624,9 @@ static void pci_acpi_setup(struct device *dev)
 	if (!adev)
 		return;
 
+	if (pci_dev->pm_cap)
+		pci_acpi_delay_optimize(pci_dev, adev);
+
 	pci_acpi_add_pm_notifier(adev, pci_dev);
 	if (!adev->wakeup.flags.valid)
 		return;
-- 
2.1.0

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