ACPI/IORT: Fix PCI ACS enablement

commit f6810c15 ("iommu/arm-smmu: Clean up early-probing
workarounds") removed kernel code that was allowing to initialize
and probe the SMMU devices early (ie earlier than PCI devices, through
linker script callback entries) in the boot process because it was not
needed any longer in that the SMMU devices/drivers now support deferred
probing.

Since the SMMUs probe routines are also in charge of requesting global
PCI ACS kernel enablement, commit f6810c15 ("iommu/arm-smmu: Clean
up early-probing workarounds") also postponed PCI ACS enablement to
SMMUs devices probe time, which is too late given that PCI devices needs
to detect if PCI ACS is enabled to init the respective capability
through the following call path:

pci_device_add()
 -> pci_init_capabilities()
  -> pci_enable_acs()

Add code in the ACPI IORT SMMU platform devices initialization path
(that is called before ACPI PCI enumeration) to detect if there
exists firmware mappings to map root complexes ids to SMMU ids
and if so enable ACS for the system.

Fixes: f6810c15 ("iommu/arm-smmu: Clean up early-probing workarounds")
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Tested-by: Nate Watterson <nwatters@codeaurora.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Hanjun Guo <hanjun.guo@linaro.org>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Cc: Zhou Wang <wangzhou1@hisilicon.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

drivers/acpi/arm64/iort.c

@@ -1178,12 +1178,44 @@ static int __init iort_add_smmu_platform_device(struct acpi_iort_node *node)
 	return ret;
 }
 
+static bool __init iort_enable_acs(struct acpi_iort_node *iort_node)
+{
+	if (iort_node->type == ACPI_IORT_NODE_PCI_ROOT_COMPLEX) {
+		struct acpi_iort_node *parent;
+		struct acpi_iort_id_mapping *map;
+		int i;
+
+		map = ACPI_ADD_PTR(struct acpi_iort_id_mapping, iort_node,
+				   iort_node->mapping_offset);
+
+		for (i = 0; i < iort_node->mapping_count; i++, map++) {
+			if (!map->output_reference)
+				continue;
+
+			parent = ACPI_ADD_PTR(struct acpi_iort_node,
+					iort_table,  map->output_reference);
+			/*
+			 * If we detect a RC->SMMU mapping, make sure
+			 * we enable ACS on the system.
+			 */
+			if ((parent->type == ACPI_IORT_NODE_SMMU) ||
+				(parent->type == ACPI_IORT_NODE_SMMU_V3)) {
+				pci_request_acs();
+				return true;
+			}
+		}
+	}
+
+	return false;
+}
+
 static void __init iort_init_platform_devices(void)
 {
 	struct acpi_iort_node *iort_node, *iort_end;
 	struct acpi_table_iort *iort;
 	struct fwnode_handle *fwnode;
 	int i, ret;
+	bool acs_enabled = false;
 
 	/*
 	 * iort_table and iort both point to the start of IORT table, but
@@ -1203,6 +1235,9 @@ static void __init iort_init_platform_devices(void)
 			return;
 		}
 
+		if (!acs_enabled)
+			acs_enabled = iort_enable_acs(iort_node);
+
 		if ((iort_node->type == ACPI_IORT_NODE_SMMU) ||
 			(iort_node->type == ACPI_IORT_NODE_SMMU_V3)) {