[PATCH 02/12] PCI/ACPI: Add PERST# Assertion Delay _DSM method

[Anshuman Gupta <anshuman.gupta@xxxxxxxxx>]

Implement _DSM Method 11 as per PCI firmware specs
section 4.6.11 Rev 3.3.

Signed-off-by: Anshuman Gupta <anshuman.gupta@xxxxxxxxx>
---
 drivers/pci/pci-acpi.c   | 53 ++++++++++++++++++++++++++++++++++++++++
 include/linux/pci-acpi.h |  7 ++++++
 2 files changed, 60 insertions(+)

diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
index ebd49e43457e..04149f037664 100644
--- a/drivers/pci/pci-acpi.c
+++ b/drivers/pci/pci-acpi.c
@@ -1499,6 +1499,59 @@ int pci_acpi_request_d3cold_aux_power(struct pci_dev *dev, u32 requested_power)
 }
 EXPORT_SYMBOL(pci_acpi_request_d3cold_aux_power);
 
+/**
+ * pci_acpi_add_perst_assertion_delay - Request PERST# delay via ACPI DSM
+ * @dev: PCI device instance
+ * @delay_us: Requested delay_us
+ *
+ * This function sends a request to the host BIOS via ACPI _DSM to grant the
+ * required PERST# delay for the specified PCI device. It evaluates the _DSM
+ * to request the PERST# delay and handles the response accordingly.
+ *
+ * Return: returns 0 on success and errno on failure.
+ */
+int pci_acpi_add_perst_assertion_delay(struct pci_dev *dev, u32 delay_us)
+{
+	union acpi_object in_obj = {
+		.integer.type = ACPI_TYPE_INTEGER,
+		.integer.value = delay_us,
+	};
+
+	union acpi_object *out_obj;
+	acpi_handle handle;
+	int result, ret = -EINVAL;
+
+	if (!dev || !ACPI_HANDLE(&dev->dev))
+		return -EINVAL;
+
+	handle = ACPI_HANDLE(&dev->dev);
+
+	out_obj = acpi_evaluate_dsm_typed(handle, &pci_acpi_dsm_guid, 4,
+					  DSM_PCI_PERST_ASSERTION_DELAY,
+					  &in_obj, ACPI_TYPE_INTEGER);
+	if (!out_obj)
+		return -EINVAL;
+
+	result = out_obj->integer.value;
+
+	if (result == delay_us) {
+		dev_info(&dev->dev, "PERST# Assertion Delay set to"
+			 "%u microseconds\n", delay_us);
+		ret = 0;
+	} else if (result == 0) {
+		dev_warn(&dev->dev, "PERST# Assertion Delay request failed,"
+			 "no previous valid request\n");
+	} else {
+		dev_warn(&dev->dev,
+			 "PERST# Assertion Delay request failed"
+			 "Previous valid delay: %u microseconds\n", result);
+	}
+
+	ACPI_FREE(out_obj);
+	return ret;
+}
+EXPORT_SYMBOL(pci_acpi_add_perst_assertion_delay);
+
 static void pci_acpi_set_external_facing(struct pci_dev *dev)
 {
 	u8 val;
diff --git a/include/linux/pci-acpi.h b/include/linux/pci-acpi.h
index dbc4b0ed433c..4b7373f91a9a 100644
--- a/include/linux/pci-acpi.h
+++ b/include/linux/pci-acpi.h
@@ -122,6 +122,7 @@ extern const guid_t pci_acpi_dsm_guid;
 #define DSM_PCI_POWER_ON_RESET_DELAY		0x08
 #define DSM_PCI_DEVICE_READINESS_DURATIONS	0x09
 #define DSM_PCI_D3COLD_AUX_POWER_LIMIT		0x0A
+#define DSM_PCI_PERST_ASSERTION_DELAY		0x0B
 
 #ifdef CONFIG_PCIE_EDR
 void pci_acpi_add_edr_notifier(struct pci_dev *pdev);
@@ -134,6 +135,7 @@ static inline void pci_acpi_remove_edr_notifier(struct pci_dev *pdev) { }
 int pci_acpi_set_companion_lookup_hook(struct acpi_device *(*func)(struct pci_dev *));
 void pci_acpi_clear_companion_lookup_hook(void);
 int pci_acpi_request_d3cold_aux_power(struct pci_dev *dev, u32 requested_power);
+int pci_acpi_add_perst_assertion_delay(struct pci_dev *dev, u32 delay_us);
 
 #else	/* CONFIG_ACPI */
 static inline void acpi_pci_add_bus(struct pci_bus *bus) { }
@@ -142,6 +144,11 @@ int pci_acpi_request_d3cold_aux_power(struct pci_dev *dev, u32 requested_power)
 {
 	return -EOPNOTSUPP;
 }
+
+int pci_acpi_add_perst_assertion_delay(struct pci_dev *dev, u32 delay_us)
+{
+	return -EOPNOTSUPP;
+}
 #endif	/* CONFIG_ACPI */
 
 #endif	/* _PCI_ACPI_H_ */
-- 
2.43.0