[v2,4/4] platform/x86/amd: pmc: Add support for using constraints to decide D3 policy

Commit Message

Mario Limonciello Dec. 3, 2023, 4:10 a.m. UTC

The default kernel policy will allow modern machines to effectively put
all PCIe bridges into PCI D3. This policy doesn't match what Windows uses.

In Windows the driver stack includes a "Power Engine Plugin" (uPEP driver)
to decide the policy for integrated devices using PEP device constraints.

Device constraints are expressed as a number in the _DSM of the PNP0D80
device and exported by the kernel in acpi_get_lps0_constraint().

Add support for SoCs to use constraints on Linux as well for deciding
target state for integrated PCI bridges.

Disable existing production SoCs by default with this change.

Link: https://learn.microsoft.com/en-us/windows-hardware/design/device-experiences/platform-design-for-modern-standby#low-power-core-silicon-cpu-soc-dram
Acked-by: Hans de Goede <[e-mail]>
Signed-off-by: Mario Limonciello <[e-mail]>
---
 drivers/platform/x86/amd/pmc/pmc.c | 57 ++++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)

Patch

diff --git a/drivers/platform/x86/amd/pmc/pmc.c b/drivers/platform/x86/amd/pmc/pmc.c
index c3104714b480..9aa6cf4fabf1 100644
--- a/drivers/platform/x86/amd/pmc/pmc.c
+++ b/drivers/platform/x86/amd/pmc/pmc.c
@@ -793,6 +793,61 @@  static int amd_pmc_czn_wa_irq1(struct amd_pmc_dev *pdev)
 	return 0;
 }
 
+static inline void amd_pmc_apply_constraint(struct pci_dev *pci_dev, bool apply)
+{
+	if (apply)
+		pci_d3cold_disable(pci_dev);
+	else
+		pci_d3cold_enable(pci_dev);
+}
+
+/*
+ * Constraints are specified in the ACPI LPS0 device and specify what the
+ * platform intended for devices that are internal to the SoC.
+ *
+ * If a constraint is present and >= to ACPI_STATE_D3, then enable D3.
+ * If a constraint is not present or < ACPI_STATE_D3, then disable D3.
+ */
+static void amd_pmc_check_constraints(struct amd_pmc_dev *pdev, bool apply)
+{
+	struct pci_dev *pci_dev = NULL;
+	struct acpi_device *adev;
+	int constraint;
+
+	switch (pdev->cpu_id) {
+	case AMD_CPU_ID_RV:
+	case AMD_CPU_ID_RN:
+	case AMD_CPU_ID_YC:
+	case AMD_CPU_ID_CB:
+	case AMD_CPU_ID_PS:
+	case AMD_CPU_ID_SP:
+		return;
+	default:
+		break;
+	}
+
+	while ((pci_dev = pci_get_device(PCI_ANY_ID, PCI_ANY_ID, pci_dev))) {
+		adev = ACPI_COMPANION(&pci_dev->dev);
+		if (!adev)
+			continue;
+		constraint = acpi_get_lps0_constraint(adev);
+		dev_dbg(&pci_dev->dev, "constraint is %d\n", constraint);
+
+		switch (constraint) {
+		case ACPI_STATE_UNKNOWN:
+		case ACPI_STATE_D0:
+		case ACPI_STATE_D1:
+		case ACPI_STATE_D2:
+			amd_pmc_apply_constraint(pci_dev, apply);
+			continue;
+		/* use the logic pci_bridge_d3_possible() to decide */
+		case ACPI_STATE_D3:
+		default:
+			continue;
+		}
+	}
+}
+
 static int amd_pmc_verify_czn_rtc(struct amd_pmc_dev *pdev, u32 *arg)
 {
 	struct rtc_device *rtc_device;
@@ -1099,6 +1154,7 @@  static int amd_pmc_probe(struct platform_device *pdev)
 			amd_pmc_quirks_init(dev);
 	}
 
+	amd_pmc_check_constraints(dev, TRUE);
 	amd_pmc_dbgfs_register(dev);
 	pm_report_max_hw_sleep(U64_MAX);
 	return 0;
@@ -1114,6 +1170,7 @@  static void amd_pmc_remove(struct platform_device *pdev)
 
 	if (IS_ENABLED(CONFIG_SUSPEND))
 		acpi_unregister_lps0_dev(&amd_pmc_s2idle_dev_ops);
+	amd_pmc_check_constraints(dev, FALSE);
 	amd_pmc_dbgfs_unregister(dev);
 	pci_dev_put(dev->rdev);
 	mutex_destroy(&dev->lock);