[PATCH v4 03/11] PCI/ACPI: Add PERST# Assertion Delay _DSM method

[Badal Nilawar <badal.nilawar@intel.com>]

From: Anshuman Gupta <anshuman.gupta@intel.com>

Implement _DSM Method 0Bh as per PCI firmware specs
section 4.6.11 Rev 3.3.

Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
Signed-off-by: Badal Nilawar <badal.nilawar@intel.com>
---
 drivers/pci/pci-acpi.c   | 57 ++++++++++++++++++++++++++++++++++++++++
 include/linux/pci-acpi.h |  8 +++++-
 2 files changed, 64 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
index d33efba4ca94..88044491feaa 100644
--- a/drivers/pci/pci-acpi.c
+++ b/drivers/pci/pci-acpi.c
@@ -1531,6 +1531,63 @@ int pci_acpi_request_d3cold_aux_power(struct pci_dev *dev, u32 requested_power,
 }
 EXPORT_SYMBOL_GPL(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)
+		return -EINVAL;
+
+	handle = ACPI_HANDLE(&dev->dev);
+	if (!handle)
+		return -EINVAL;
+
+	if (!acpi_check_dsm(handle, &pci_acpi_dsm_guid, 4, 1 << DSM_PCI_PERST_ASSERTION_DELAY)) {
+		pci_dbg(dev, "ACPI _DSM 0%Xh not supported\n", DSM_PCI_PERST_ASSERTION_DELAY);
+		return -ENODEV;
+	}
+
+	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) {
+		pci_info(dev, "PERST# Assertion Delay set to %u microseconds\n", delay_us);
+		ret = 0;
+	} else if (result == 0) {
+		pci_warn(dev, "PERST# Assertion Delay request failed, no previous valid request\n");
+	} else {
+		pci_warn(dev, "PERST# Assertion Delay request failed, Previous valid delay: %u microseconds\n",
+			 result);
+	}
+
+	ACPI_FREE(out_obj);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(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 6079306ad754..e53d4893cf56 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);
@@ -135,7 +136,7 @@ int pci_acpi_set_companion_lookup_hook(struct acpi_device *(*func)(struct pci_de
 void pci_acpi_clear_companion_lookup_hook(void);
 int pci_acpi_request_d3cold_aux_power(struct pci_dev *dev, u32 requested_power,
 				      u32 *retry_interval);
-
+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) { }
 static inline void acpi_pci_remove_bus(struct pci_bus *bus) { }
@@ -144,6 +145,11 @@ static inline int pci_acpi_request_d3cold_aux_power(struct pci_dev *dev, u32 req
 {
 	return -EOPNOTSUPP;
 }
+
+static inline int pci_acpi_add_perst_assertion_delay(struct pci_dev *dev, u32 delay_us)
+{
+	return -EOPNOTSUPP;
+}
 #endif	/* CONFIG_ACPI */
 
 #endif	/* _PCI_ACPI_H_ */
-- 
2.34.1