diff --git a/drivers/arm/mhu/mhu_v3_x_private.h b/drivers/arm/mhu/mhu_v3_x_private.h
new file mode 100644
index 0000000..9594a2a
--- /dev/null
+++ b/drivers/arm/mhu/mhu_v3_x_private.h
@@ -0,0 +1,222 @@
+/*
+ * Copyright (c) 2024, Arm Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#ifndef MHU_V3_X_PRIVATE_H
+#define MHU_V3_X_PRIVATE_H
+
+#include <stdint.h>
+
+/* Flag for PDBCW Interrupt Transfer Acknowledgment  */
+#define MHU_V3_X_PDBCW_INT_X_TFR_ACK 0x1
+
+/* Flag for PDBCW CTRL Postbox combined interrupts enable */
+#define MHU_V3_X_PDBCW_CTRL_PBX_COMB_EN 0x1
+
+/* Flag for MDBCW CTRL Mailbox combined interrupts enable */
+#define MHU_V3_X_MDBCW_CTRL_MBX_COMB_EN 0x1
+
+/**
+ * Postbox control page structure
+ */
+struct _mhu_v3_x_pbx_ctrl_reg_t {
+	/* Offset: 0x000 (R/ ) Postbox Block Identifier */
+	const volatile uint32_t pbx_blk_id;
+	/* Offset: 0x004 (R/ ) Reserved */
+	const volatile uint8_t reserved_0[0x10 - 0x04];
+	/* Offset: 0x010 (R/ ) Postbox Feature Support 0 */
+	const volatile uint32_t pbx_feat_spt0;
+	/* Offset: 0x014 (R/ ) Postbox Feature Support 1 */
+	const volatile uint32_t pbx_feat_spt1;
+	/* Offset: 0x018 (R/ ) Reserved */
+	const volatile uint8_t reserved_1[0x20 - 0x18];
+	/* Offset: 0x020 (R/ ) Postbox Doorbell Channel Configuration 0 */
+	const volatile uint32_t pbx_dbch_cfg0;
+	/* Offset: 0x024 (R/ ) Reserved */
+	const volatile uint8_t reserved_2[0x30 - 0x24];
+	/* Offset: 0x030 (R/ ) Postbox FIFO Channel Configuration 0 */
+	const volatile uint32_t pbx_ffch_cfg0;
+	/* Offset: 0x034 (R/ ) Reserved */
+	const volatile uint8_t reserved_3[0x40 - 0x34];
+	/* Offset: 0x040 (R/ ) Postbox Fast Channel Configuration 0 */
+	const volatile uint32_t pbx_fch_cfg0;
+	/* Offset: 0x044 (R/ ) Reserved */
+	const volatile uint8_t reserved_4[0x100 - 0x44];
+	/* Offset: 0x100 (R/W) Postbox control */
+	volatile uint32_t pbx_ctrl;
+	/* Offset: 0x164 (R/ ) Reserved */
+	const volatile uint8_t reserved_5[0x400 - 0x104];
+	/*
+	 * Offset: 0x400 (R/ ) Postbox Doorbell Channel Interrupt Status n,
+	 * where n is 0 - 3.
+	 */
+	const volatile uint32_t pbx_dbch_int_st[4];
+	/*
+	 * Offset: 0x410 (R/ ) Postbox FIFO Channel <n> Interrupt Status n,
+	 * where n is 0 - 1.
+	 */
+	const volatile uint32_t pbx_ffch_int_st[2];
+	/* Offset: 0x418 (R/ ) Reserved */
+	const uint8_t reserved_6[0xFC8 - 0x418];
+	/* Offset: 0xFC8 (R/ ) Postbox Implementer Identification Register */
+	const volatile uint32_t pbx_iidr;
+	/* Offset: 0xFCC (R/ ) Postbox Architecture Identification Register */
+	const volatile uint32_t pbx_aidr;
+	/*
+	 * Offset: 0xFD0 (R/ ) Postbox Implementation Defined Identification
+	 * Register n, where n is 0 - 11.
+	 */
+	const volatile uint32_t impl_def_id[12];
+};
+
+/**
+ * Postbox doorbell channel window page structure
+ */
+struct _mhu_v3_x_pdbcw_reg_t {
+	/* Offset: 0x000 (R/ ) Postbox Doorbell Channel Window Status */
+	const volatile uint32_t pdbcw_st;
+	/* Offset: 0x004 (R/ ) Reserved */
+	const uint8_t reserved_0[0xC - 0x4];
+	/* Offset: 0x00C ( /W) Postbox Doorbell Channel Window Set */
+	volatile uint32_t pdbcw_set;
+	/*
+	 * Offset: 0x010 (R/ ) Postbox Doorbell Channel Window Interrupt Status
+	 */
+	const volatile uint32_t pdbcw_int_st;
+	/*
+	 * Offset: 0x014 ( /W) Postbox Doorbell Channel Window Interrupt Clear
+	 */
+	volatile uint32_t pdbcw_int_clr;
+	/*
+	 * Offset: 0x018 (R/W) Postbox Doorbell Channel Window Interrupt Enable
+	 */
+	volatile uint32_t pdbcw_int_en;
+	/* Offset: 0x01C (R/W) Postbox Doorbell Channel Window Control */
+	volatile uint32_t pdbcw_ctrl;
+};
+
+/**
+ * Postbox structure
+ */
+struct _mhu_v3_x_pbx {
+	/* Postbox Control */
+	struct _mhu_v3_x_pbx_ctrl_reg_t pbx_ctrl_page;
+	/* Postbox Doorbell Channel Window */
+	struct _mhu_v3_x_pdbcw_reg_t pdbcw_page;
+};
+
+/**
+ * Mailbox control page structure
+ */
+struct _mhu_v3_x_mbx_ctrl_reg_t {
+	/* Offset: 0x000 (R/ ) Mailbox Block Identifier */
+	const volatile uint32_t mbx_blk_id;
+	/* Offset: 0x004 (R/ ) Reserved */
+	const volatile uint8_t reserved_0[0x10 - 0x04];
+	/* Offset: 0x010 (R/ ) Mailbox Feature Support 0 */
+	const volatile uint32_t mbx_feat_spt0;
+	/* Offset: 0x014 (R/ ) Mailbox Feature Support 1 */
+	const volatile uint32_t mbx_feat_spt1;
+	/* Offset: 0x018 (R/ ) Reserved */
+	const volatile uint8_t reserved_1[0x20 - 0x18];
+	/* Offset: 0x020 (R/ ) Mailbox Doorbell Channel Configuration 0 */
+	const volatile uint32_t mbx_dbch_cfg0;
+	/* Offset: 0x024 (R/ ) Reserved */
+	const volatile uint8_t reserved_2[0x30 - 0x24];
+	/* Offset: 0x030 (R/ ) Mailbox FIFO Channel Configuration 0 */
+	const volatile uint32_t mbx_ffch_cfg0;
+	/* Offset: 0x034 (R/ ) Reserved */
+	const volatile uint8_t reserved_4[0x40 - 0x34];
+	/* Offset: 0x040 (R/ ) Mailbox Fast Channel Configuration 0 */
+	const volatile uint32_t mbx_fch_cfg0;
+	/* Offset: 0x044 (R/ ) Reserved */
+	const volatile uint8_t reserved_5[0x100 - 0x44];
+	/* Offset: 0x100 (R/W) Mailbox control */
+	volatile uint32_t mbx_ctrl;
+	/* Offset: 0x104 (R/ ) Reserved */
+	const volatile uint8_t reserved_6[0x140 - 0x104];
+	/* Offset: 0x140 (R/W) Mailbox Fast Channel control */
+	volatile uint32_t mbx_fch_ctrl;
+	/* Offset: 0x144 (R/W) Mailbox Fast Channel Group Interrupt Enable */
+	volatile uint32_t mbx_fcg_int_en;
+	/* Offset: 0x148 (R/ ) Reserved */
+	const volatile uint8_t reserved_7[0x400 - 0x148];
+	/*
+	 * Offset: 0x400 (R/ ) Mailbox Doorbell Channel Interrupt Status n,
+	 * where n = 0 - 3.
+	 */
+	const volatile uint32_t mbx_dbch_int_st[4];
+	/*
+	 * Offset: 0x410 (R/ ) Mailbox FIFO Channel Interrupt Status n, where
+	 * n = 0 - 1.
+	 */
+	const volatile uint32_t mbx_ffch_int_st[2];
+	/* Offset: 0x418 (R/ ) Reserved */
+	const volatile uint8_t reserved_8[0x470 - 0x418];
+	/* Offset: 0x470 (R/ ) Mailbox Fast Channel Group Interrupt Status */
+	const volatile uint32_t mbx_fcg_int_st;
+	/* Offset: 0x474 (R/ ) Reserved */
+	const volatile uint8_t reserved_9[0x480 - 0x474];
+	/*
+	 * Offset: 0x480 (R/ ) Mailbox Fast Channel Group <n> Interrupt Status,
+	 * where n = 0 - 31.
+	 */
+	const volatile uint32_t mbx_fch_grp_int_st[32];
+	/* Offset: 0x500 (R/ ) Reserved */
+	const volatile uint8_t reserved_10[0xFC8 - 0x500];
+	/* Offset: 0xFC8 (R/ ) Mailbox Implementer Identification Register */
+	const volatile uint32_t mbx_iidr;
+	/* Offset: 0xFCC (R/ ) Mailbox Architecture Identification Register */
+	const volatile uint32_t mbx_aidr;
+	/*
+	 * Offset: 0xFD0 (R/ ) Mailbox Implementation Defined Identification
+	 * Register n, where n is 0 - 11.
+	 */
+	const volatile uint32_t impl_def_id[12];
+};
+
+/**
+ * Mailbox doorbell channel window page structure
+ */
+struct _mhu_v3_x_mdbcw_reg_t {
+	/* Offset: 0x000 (R/ ) Mailbox Doorbell Channel Window Status */
+	const volatile uint32_t mdbcw_st;
+	/* Offset: 0x004 (R/ ) Mailbox Doorbell Channel Window Status Masked */
+	const volatile uint32_t mdbcw_st_msk;
+	/* Offset: 0x008 ( /W) Mailbox Doorbell Channel Window Clear */
+	volatile uint32_t mdbcw_clr;
+	/* Offset: 0x00C (R/ ) Reserved */
+	const volatile uint8_t reserved_0[0x10 - 0x0C];
+	/* Offset: 0x010 (R/ ) Mailbox Doorbell Channel Window Mask Status */
+	const volatile uint32_t mdbcw_msk_st;
+	/* Offset: 0x014 ( /W) Mailbox Doorbell Channel Window Mask Set */
+	volatile uint32_t mdbcw_msk_set;
+	/* Offset: 0x018 ( /W) Mailbox Doorbell Channel Window Mask Clear */
+	volatile uint32_t mdbcw_msk_clr;
+	/* Offset: 0x01C (R/W) Mailbox Doorbell Channel Window Control */
+	volatile uint32_t mdbcw_ctrl;
+};
+
+/**
+ * Mailbox structure
+ */
+struct _mhu_v3_x_mbx {
+	/* Mailbox control */
+	struct _mhu_v3_x_mbx_ctrl_reg_t mbx_ctrl_page;
+	/* Mailbox Doorbell Channel Window */
+	struct _mhu_v3_x_mdbcw_reg_t mdbcw_page;
+};
+
+/**
+ * MHUv3 frame type
+ */
+union _mhu_v3_x_frame_t {
+	/* Postbox Frame */
+	struct _mhu_v3_x_pbx pbx_frame;
+	/* Mailbox Frame */
+	struct _mhu_v3_x_mbx mbx_frame;
+};
+
+#endif /* MHU_V3_X_PRIVATE_H */