diff --git a/hypervisor/arch/x86/assign.c b/hypervisor/arch/x86/assign.c
index 33504538b..93bd32a9e 100644
--- a/hypervisor/arch/x86/assign.c
+++ b/hypervisor/arch/x86/assign.c
@@ -532,8 +532,6 @@ void ptdev_intx_ack(struct acrn_vm *vm, uint8_t virt_pin,
  * We use entry_nr to indicate coming vectors
  * entry_nr = 0 means first vector
  * user must provide bdf and entry_nr
- *
- * This function is called by SOS pci MSI config routine through hcall
  */
 int ptdev_msix_remap(struct acrn_vm *vm, uint16_t virt_bdf,
 		uint16_t entry_nr, struct ptdev_msi_info *info)
diff --git a/hypervisor/include/arch/x86/assign.h b/hypervisor/include/arch/x86/assign.h
index 28f38bc1a..4d68370ba 100644
--- a/hypervisor/include/arch/x86/assign.h
+++ b/hypervisor/include/arch/x86/assign.h
@@ -9,18 +9,157 @@
 
 #include <ptdev.h>
 
-void ptdev_intx_ack(struct acrn_vm *vm, uint8_t virt_pin,
-		enum ptdev_vpin_source vpin_src);
-int ptdev_msix_remap(struct acrn_vm *vm, uint16_t virt_bdf,
-		uint16_t entry_nr, struct ptdev_msi_info *info);
-int ptdev_intx_pin_remap(struct acrn_vm *vm, uint8_t virt_pin,
-		enum ptdev_vpin_source vpin_src);
-int ptdev_add_intx_remapping(struct acrn_vm *vm, uint8_t virt_pin, uint8_t phys_pin,
-		bool pic_pin);
+/**
+ * @file assign.h
+ *
+ * @brief public APIs for Passthrough Interrupt Remapping
+ */
+
+/**
+ * @brief VT-d
+ *
+ * @defgroup acrn_passthrough ACRN Passthrough
+ * @{
+ */
+
+/**
+ * @brief Acknowledge a virtual interrupt for passthrough device.
+ *
+ * Acknowledge a virtual legacy interrupt for a passthrough device.
+ *
+ * @param[in] vm pointer to acrn_vm
+ * @param[in] virt_pin virtual pin number associated with the passthrough device
+ * @param[in] vpin_src ioapic or pic
+ *
+ * @return None
+ *
+ * @pre vm != NULL
+ *
+ */
+void ptdev_intx_ack(struct acrn_vm *vm, uint8_t virt_pin, enum ptdev_vpin_source vpin_src);
+
+/**
+ * @brief MSI/MSI-x remapping for passthrough device.
+ *
+ * Main entry for PCI device assignment with MSI and MSI-X.
+ * MSI can up to 8 vectors and MSI-X can up to 1024 Vectors.
+ *
+ * @param[in] vm pointer to acrn_vm
+ * @param[in] virt_bdf virtual bdf associated with the passthrough device
+ * @param[in] entry_nr indicate coming vectors, entry_nr = 0 means first vector
+ * @param[in] info structure used for MSI/MSI-x remapping
+ *
+ * @return
+ *    - 0: on success
+ *    - \p -ENODEV:
+ *      - for SOS, the entry already be held by others
+ *      - for UOS, no pre-hold mapping found.
+ *
+ * @pre vm != NULL
+ * @pre info != NULL
+ *
+ */
+int ptdev_msix_remap(struct acrn_vm *vm, uint16_t virt_bdf, uint16_t entry_nr, struct ptdev_msi_info *info);
+
+
+/**
+ * @brief INTx remapping for passthrough device.
+ *
+ * Set up the remapping of the given virtual pin for the given vm.
+ * This is the main entry for PCI/Legacy device assignment with INTx, calling from vIOAPIC or vPIC.
+ *
+ * @param[in] vm pointer to acrn_vm
+ * @param[in] virt_pin virtual pin number associated with the passthrough device
+ * @param[in] vpin_src ioapic or pic
+ *
+ * @return
+ *    - 0: on success
+ *    - \p -ENODEV:
+ *      - for SOS, the entry already be held by others
+ *      - for UOS, no pre-hold mapping found.
+ *
+ * @pre vm != NULL
+ *
+ */
+int ptdev_intx_pin_remap(struct acrn_vm *vm, uint8_t virt_pin, enum ptdev_vpin_source vpin_src);
+
+/**
+ * @brief Add an interrupt remapping entry for INTx as pre-hold mapping.
+ *
+ * Except vm0, Device Model should call this function to pre-hold ptdev intx
+ * The entry is identified by phys_pin, one entry vs. one phys_pin.
+ * Currently, one phys_pin can only be held by one pin source (vPIC or vIOAPIC).
+ *
+ * @param[in] vm pointer to acrn_vm
+ * @param[in] virt_pin virtual pin number associated with the passthrough device
+ * @param[in] phys_pin physical pin number associated with the passthrough device
+ * @param[in] pic_pin true for pic, false for ioapic
+ *
+ * @return
+ *    - 0: on success
+ *    - \p -EINVAL: invalid virt_pin value
+ *    - \p -ENODEV: failed to add the remapping entry
+ *
+ * @pre vm != NULL
+ *
+ */
+int ptdev_add_intx_remapping(struct acrn_vm *vm, uint8_t virt_pin, uint8_t phys_pin, bool pic_pin);
+
+/**
+ * @brief Remove an interrupt remapping entry for INTx.
+ *
+ * Deactivate & remove mapping entry of the given virt_pin for given vm.
+ *
+ * @param[in] vm pointer to acrn_vm
+ * @param[in] virt_pin virtual pin number associated with the passthrough device
+ * @param[in] pic_pin true for pic, false for ioapic
+ *
+ * @return None
+ *
+ * @pre vm != NULL
+ *
+ */
 void ptdev_remove_intx_remapping(const struct acrn_vm *vm, uint8_t virt_pin, bool pic_pin);
-int ptdev_add_msix_remapping(struct acrn_vm *vm, uint16_t virt_bdf,
-	uint16_t phys_bdf, uint32_t vector_count);
-void ptdev_remove_msix_remapping(const struct acrn_vm *vm, uint16_t virt_bdf,
-		uint32_t vector_count);
+
+/**
+ * @brief Add interrupt remapping entry/entries for MSI/MSI-x as pre-hold mapping.
+ *
+ * Add pre-hold mapping of the given number of vectors between the given physical and virtual BDF for the given vm.
+ * Except vm0, Device Model should call this function to pre-hold ptdev MSI/MSI-x.
+ * The entry is identified by phys_bdf:msi_idx, one entry vs. one phys_bdf:msi_idx.
+ *
+ * @param[in] vm pointer to acrn_vm
+ * @param[in] virt_bdf virtual bdf associated with the passthrough device
+ * @param[in] phys_bdf physical bdf associated with the passthrough device
+ * @param[in] vector_count number of vectors
+ *
+ * @return
+ *    - 0: on success
+ *    - \p -ENODEV: failed to add the remapping entry
+ *
+ * @pre vm != NULL
+ *
+ */
+int ptdev_add_msix_remapping(struct acrn_vm *vm, uint16_t virt_bdf, uint16_t phys_bdf, uint32_t vector_count);
+
+/**
+ * @brief Remove interrupt remapping entry/entries for MSI/MSI-x.
+ *
+ * Remove the mapping of given number of vectors of the given virtual BDF for the given vm.
+ *
+ * @param[in] vm pointer to acrn_vm
+ * @param[in] virt_bdf virtual bdf associated with the passthrough device
+ * @param[in] vector_count number of vectors
+ *
+ * @return None
+ *
+ * @pre vm != NULL
+ *
+ */
+void ptdev_remove_msix_remapping(const struct acrn_vm *vm, uint16_t virt_bdf, uint32_t vector_count);
+
+/**
+  * @}
+  */
 
 #endif /* ASSIGN_H */