ACPI/IORT: Enable special index ITS group mappings for IORT nodes

IORT revision C introduced SMMUv3 and PMCG MSI support by adding
specific mapping entries in the SMMUv3/PMCG subtables to retrieve
the device ID and the ITS group it maps to for a given SMMUv3/PMCG
IORT node.

Introduce a mapping function (ie iort_get_id_mapping_index()), that
for a given IORT node looks up if an ITS specific ID mapping entry
exists and if so retrieve the corresponding mapping index in the IORT
node mapping array.

Since an ITS specific index mapping can be present for an IORT
node that is not a leaf node (eg SMMUv3 - to describe its own
ITS device ID) special handling is required for two steps mapping
cases such as PCI/NamedComponent--->SMMUv3--->ITS because the SMMUv3
ITS specific index mapping entry should be skipped to prevent the
IORT API from considering the mapping entry as a regular mapping one.

If we take the following IORT topology example:

|----------------------|
|  Root Complex Node   |
|----------------------|
|    map entry[x]      |
|----------------------|
|       id value       |
| output_reference     |
|---|------------------|
    |
    |   |----------------------|
    |-->|        SMMUv3        |
        |----------------------|
        |     SMMUv3 dev ID    |
        |     mapping index 0  |
        |----------------------|
        |      map entry[0]    |
        |----------------------|
        |       id value       |
        | output_reference-----------> ITS 1 (SMMU MSI domain)
        |----------------------|
        |      map entry[1]    |
        |----------------------|
        |       id value       |
        | output_reference-----------> ITS 2 (PCI MSI domain)
        |----------------------|

where the SMMUv3 ITS specific mapping entry is index 0 and it
represents the SMMUv3 ITS specific index mapping entry (describing its
own ITS device ID), we need to skip that mapping entry while carrying
out the Root Complex Node regular mappings to prevent erroneous
translations.

Reuse the iort_get_id_mapping_index() function to detect the ITS
specific mapping index for a specific IORT node and skip it in the IORT
mapping API (ie iort_node_map_id()) loop to prevent considering it a
normal PCI/Named Component ID mapping entry.
Signed-off-by: Hanjun Guo <hanjun.guo@linaro.org>
[lorenzo.pieralisi@arm.com: split patch/rewrote commit log]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>

drivers/acpi/arm64/iort.c

@@ -365,6 +365,11 @@ static struct acpi_iort_node *iort_node_get_id(struct acpi_iort_node *node,
 	return NULL;
 }
 
+static inline int iort_get_id_mapping_index(struct acpi_iort_node *node)
+{
+	return -EINVAL;
+}
+
 static struct acpi_iort_node *iort_node_map_id(struct acpi_iort_node *node,
 					       u32 id_in, u32 *id_out,
 					       u8 type_mask)
@@ -374,7 +379,7 @@ static struct acpi_iort_node *iort_node_map_id(struct acpi_iort_node *node,
 	/* Parse the ID mapping tree to find specified node type */
 	while (node) {
 		struct acpi_iort_id_mapping *map;
-		int i;
+		int i, index;
 
 		if (IORT_TYPE_MASK(node->type) & type_mask) {
 			if (id_out)
@@ -395,8 +400,19 @@ static struct acpi_iort_node *iort_node_map_id(struct acpi_iort_node *node,
 			goto fail_map;
 		}
 
+		/*
+		 * Get the special ID mapping index (if any) and skip its
+		 * associated ID map to prevent erroneous multi-stage
+		 * IORT ID translations.
+		 */
+		index = iort_get_id_mapping_index(node);
+
 		/* Do the ID translation */
 		for (i = 0; i < node->mapping_count; i++, map++) {
+			/* if it is special mapping index, skip it */
+			if (i == index)
+				continue;
+
 			if (!iort_id_map(map, node->type, id, &id))
 				break;
 		}
@@ -505,16 +521,24 @@ u32 iort_msi_map_rid(struct device *dev, u32 req_id)
  */
 int iort_pmsi_get_dev_id(struct device *dev, u32 *dev_id)
 {
-	int i;
+	int i, index;
 	struct acpi_iort_node *node;
 
 	node = iort_find_dev_node(dev);
 	if (!node)
 		return -ENODEV;
 
-	for (i = 0; i < node->mapping_count; i++) {
-		if (iort_node_map_platform_id(node, dev_id, IORT_MSI_TYPE, i))
+	index = iort_get_id_mapping_index(node);
+	/* if there is a valid index, go get the dev_id directly */
+	if (index >= 0) {
+		if (iort_node_get_id(node, dev_id, index))
 			return 0;
+	} else {
+		for (i = 0; i < node->mapping_count; i++) {
+			if (iort_node_map_platform_id(node, dev_id,
+						      IORT_MSI_TYPE, i))
+				return 0;
+		}
 	}
 
 	return -ENODEV;