diff --git a/Documentation/devicetree/bindings/interrupt-controller/arm,gic-v3.txt b/Documentation/devicetree/bindings/interrupt-controller/arm,gic-v3.txt
index 4c29cdab0ea5..0798a61bbf99 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: (u32, u32) tuple describing the host address
+  and size of the pre-ITS window, as implemented on the Socionext Synquacer SoC
+
 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 0df64a6a56d4..c4361dff2b74 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -539,6 +539,14 @@ 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 891de07fd4cc..2fc4fba0cc4c 100644
--- a/drivers/irqchip/irq-gic-v3-its.c
+++ b/drivers/irqchip/irq-gic-v3-its.c
@@ -97,12 +97,18 @@ struct its_node {
 	struct its_cmd_block	*cmd_write;
 	struct its_baser	tables[GITS_BASER_NR_REGS];
 	struct its_collection	*collections;
+	struct fwnode_handle	*fwnode_handle;
 	struct list_head	its_device_list;
 	u64			flags;
 	u32			ite_size;
 	u32			device_ids;
 	int			numa_node;
+	unsigned int		msi_domain_flag_mask;
 	bool			is_v4;
+
+	/* for Socionext Synquacer pre-ITS */
+	u32			pre_its_base;
+	u32			pre_its_size;
 };
 
 #define ITS_ITT_ALIGN		SZ_256
@@ -1095,14 +1101,29 @@ 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_device *its_dev)
+{
+	struct its_node *its = its_dev->its;
+
+	if (unlikely(its->pre_its_size > 0))
+		/*
+		 * 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);
+
+	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);
-	struct its_node *its;
 	u64 addr;
 
-	its = its_dev->its;
-	addr = its->phys_base + GITS_TRANSLATER;
+	addr = its_irq_get_msi_base(its_dev);
 
 	msg->address_lo		= lower_32_bits(addr);
 	msg->address_hi		= upper_32_bits(addr);
@@ -2752,6 +2773,27 @@ static void __maybe_unused its_enable_quirk_qdf2400_e0065(void *data)
 	its->ite_size = 16;
 }
 
+static void __maybe_unused its_enable_quirk_socionext_synquacer(void *data)
+{
+	struct its_node *its = data;
+	u32 pre_its_window[2];
+	u32 ids;
+
+	if (!fwnode_property_read_u32_array(its->fwnode_handle,
+					    "socionext,synquacer-pre-its",
+					    pre_its_window,
+					    ARRAY_SIZE(pre_its_window))) {
+		its->pre_its_base = pre_its_window[0];
+		its->pre_its_size = pre_its_window[1];
+
+		ids = ilog2(its->pre_its_size) - 2;
+		if (its->device_ids > ids)
+			its->device_ids = ids;
+
+		its->msi_domain_flag_mask = ~IRQ_DOMAIN_FLAG_MSI_REMAP;
+	}
+}
+
 static const struct gic_quirk its_quirks[] = {
 #ifdef CONFIG_CAVIUM_ERRATUM_22375
 	{
@@ -2777,6 +2819,19 @@ static const struct gic_quirk its_quirks[] = {
 		.init	= its_enable_quirk_qdf2400_e0065,
 	},
 #endif
+#ifdef CONFIG_SOCIONEXT_SYNQUACER_PREITS
+	{
+		/*
+		 * The Socionext Synquacer SoC incorporates ARM's own GIC-500
+		 * implementation, but with a 'pre-ITS' added that requires
+		 * special handling in software.
+		 */
+		.desc	= "ITS: Socionext Synquacer pre-ITS",
+		.iidr	= 0x0001143b,
+		.mask	= 0xffffffff,
+		.init	= its_enable_quirk_socionext_synquacer,
+	},
+#endif
 	{
 	}
 };
@@ -2806,6 +2861,7 @@ 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;
+	inner_domain->flags &= its->msi_domain_flag_mask;
 	info->ops = &its_msi_domain_ops;
 	info->data = its;
 	inner_domain->host_data = info;
@@ -2959,6 +3015,7 @@ static int __init its_probe_one(struct resource *res,
 		goto out_free_its;
 	}
 	its->cmd_write = its->cmd_base;
+	its->fwnode_handle = handle;
 
 	its_enable_quirks(its);
 
