diff --git a/Documentation/devicetree/bindings/interrupt-controller/arm,gic-v3.txt b/Documentation/devicetree/bindings/interrupt-controller/arm,gic-v3.txt
index 4c29cdab0ea5..112ebb286728 100644
--- a/Documentation/devicetree/bindings/interrupt-controller/arm,gic-v3.txt
+++ b/Documentation/devicetree/bindings/interrupt-controller/arm,gic-v3.txt
@@ -75,6 +75,10 @@ These nodes must have the following properties:
 - reg: Specifies the base physical address and size of the ITS
   registers.
 
+Optional:
+- socionext,synquacer-pre-its: (u64, u64) tuple describing the PCI address
+  and size of the pre-ITS window.
+
 The main GIC node must contain the appropriate #address-cells,
 #size-cells and ranges properties for the reg property of all ITS
 nodes.
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index dfd908630631..081722240936 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -538,6 +538,14 @@ config QCOM_QDF2400_ERRATUM_0065
 
 	  If unsure, say Y.
 
+config SOCIONEXT_SYNQUACER_PREITS
+	bool "Socionext Synquacer: Workaround for GICv3 pre-ITS"
+	default y
+	help
+	  Socionext Synquacer SoCs implement a separate h/w block to generate
+	  MSI doorbell writes with non-zero values for the device ID.
+
+	  If unsure, say Y.
 endmenu
 
 
diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
index 284738add89b..fb86b15fa10d 100644
--- a/drivers/irqchip/irq-gic-v3-its.c
+++ b/drivers/irqchip/irq-gic-v3-its.c
@@ -45,6 +45,7 @@
 #define ITS_FLAGS_CMDQ_NEEDS_FLUSHING		(1ULL << 0)
 #define ITS_FLAGS_WORKAROUND_CAVIUM_22375	(1ULL << 1)
 #define ITS_FLAGS_WORKAROUND_CAVIUM_23144	(1ULL << 2)
+#define ITS_FLAGS_WORKAROUND_SOCIONEXT_PREITS	(1ULL << 3)
 
 #define RDIST_FLAGS_PROPBASE_NEEDS_FLUSHING	(1 << 0)
 
@@ -85,6 +86,10 @@ struct its_node {
 	struct its_collection	*collections;
 	struct list_head	its_device_list;
 	u64			flags;
+#ifdef CONFIG_SOCIONEXT_SYNQUACER_PREITS
+	u64			pre_its_base;
+	u64			pre_its_size;
+#endif
 	u32			ite_size;
 	u32			device_ids;
 	int			numa_node;
@@ -654,6 +659,23 @@ static int its_set_affinity(struct irq_data *d, const struct cpumask *mask_val,
 	return IRQ_SET_MASK_OK_DONE;
 }
 
+static u64 its_irq_get_msi_base(struct its_node *its)
+{
+#ifdef CONFIG_SOCIONEXT_SYNQUACER_PREITS
+	if (its->flags & ITS_FLAGS_WORKAROUND_SOCIONEXT_PREITS)
+
+		/*
+		 * The Socionext Synquacer SoC has a so-called 'pre-ITS',
+		 * which maps 32-bit writes targeted at a separate window of
+		 * size '4 << device_id_bits' onto writes to GITS_TRANSLATER
+		 * with device ID taken from bits [device_id_bits + 1:2] of
+		 * the window offset.
+		 */
+		return its->pre_its_base + (its_dev->device_id << 2);
+#endif
+	return its->phys_base + GITS_TRANSLATER;
+}
+
 static void its_irq_compose_msi_msg(struct irq_data *d, struct msi_msg *msg)
 {
 	struct its_device *its_dev = irq_data_get_irq_chip_data(d);
@@ -661,12 +683,15 @@ static void its_irq_compose_msi_msg(struct irq_data *d, struct msi_msg *msg)
 	u64 addr;
 
 	its = its_dev->its;
-	addr = its->phys_base + GITS_TRANSLATER;
+	addr = its_irq_get_msi_base(its);
 
 	msg->address_lo		= lower_32_bits(addr);
 	msg->address_hi		= upper_32_bits(addr);
 	msg->data		= its_get_event_id(d);
 
+	if (its->flags & ITS_FLAGS_WORKAROUND_SOCIONEXT_PREITS)
+		return;
+
 	iommu_dma_map_msi_msg(d->irq, msg);
 }
 
@@ -1044,6 +1069,11 @@ static int its_alloc_tables(struct its_node *its)
 		ids     = 0x14;                 /* 20 bits, 8MB */
 	}
 
+#ifdef CONFIG_SOCIONEXT_SYNQUACER_PREITS
+	if (its->flags & ITS_FLAGS_WORKAROUND_SOCIONEXT_PREITS)
+		ids = ilog2(its->pre_its_size) - 2;
+#endif
+
 	its->device_ids = ids;
 
 	for (i = 0; i < GITS_BASER_NR_REGS; i++) {
@@ -1640,11 +1670,21 @@ static const struct gic_quirk its_quirks[] = {
 	}
 };
 
-static void its_enable_quirks(struct its_node *its)
+static void its_enable_quirks(struct its_node *its,
+			      struct fwnode_handle *handle)
 {
 	u32 iidr = readl_relaxed(its->base + GITS_IIDR);
 
 	gic_enable_quirks(iidr, its_quirks, its);
+
+#ifdef CONFIG_SOCIONEXT_SYNQUACER_PREITS
+	if (!fwnode_property_read_u64_array(handle,
+					"socionext,synquacer-pre-its",
+					&its->pre_its_base, 2)) {
+		its->flags |= ITS_FLAGS_WORKAROUND_SOCIONEXT_PREITS;
+		pr_info("ITS: enabling workaround for Socionext Synquacer pre-ITS\n");
+	}
+#endif
 }
 
 static int its_init_domain(struct fwnode_handle *handle, struct its_node *its)
@@ -1664,7 +1704,9 @@ static int its_init_domain(struct fwnode_handle *handle, struct its_node *its)
 
 	inner_domain->parent = its_parent;
 	irq_domain_update_bus_token(inner_domain, DOMAIN_BUS_NEXUS);
-	inner_domain->flags |= IRQ_DOMAIN_FLAG_MSI_REMAP;
+
+	if (!(its->flags & ITS_FLAGS_WORKAROUND_SOCIONEXT_PREITS))
+		inner_domain->flags |= IRQ_DOMAIN_FLAG_MSI_REMAP;
 	info->ops = &its_msi_domain_ops;
 	info->data = its;
 	inner_domain->host_data = info;
@@ -1724,7 +1766,7 @@ static int __init its_probe_one(struct resource *res,
 	}
 	its->cmd_write = its->cmd_base;
 
-	its_enable_quirks(its);
+	its_enable_quirks(its, handle);
 
 	err = its_alloc_tables(its);
 	if (err)
