diff --git a/embed/bootloader/main.c b/embed/bootloader/main.c
index ec1775102e..bd5d557992 100644
--- a/embed/bootloader/main.c
+++ b/embed/bootloader/main.c
@@ -162,7 +162,7 @@ void usb_init_all(void) {
     };
 
     usb_init(&dev_info);
-    ensure(0 == usb_hid_add(&hid_info), NULL);
+    ensure(usb_hid_add(&hid_info), NULL);
     usb_start();
 }
 
diff --git a/embed/extmod/modtrezorio/modtrezorio-msg.h b/embed/extmod/modtrezorio/modtrezorio-msg.h
index 6984eeec9c..78a31b951e 100644
--- a/embed/extmod/modtrezorio/modtrezorio-msg.h
+++ b/embed/extmod/modtrezorio/modtrezorio-msg.h
@@ -449,13 +449,13 @@ STATIC mp_obj_t mod_trezorio_USB_open(mp_obj_t self) {
 
         if (MP_OBJ_IS_TYPE(iface, &mod_trezorio_HID_type)) {
             mp_obj_HID_t *hid = MP_OBJ_TO_PTR(iface);
-            if (usb_hid_add(&hid->info) != 0) {
+            if (!usb_hid_add(&hid->info)) {
                 usb_deinit();
                 mp_raise_msg(&mp_type_RuntimeError, "failed to add HID interface");
             }
         } else if (MP_OBJ_IS_TYPE(iface, &mod_trezorio_VCP_type)) {
             mp_obj_VCP_t *vcp = MP_OBJ_TO_PTR(iface);
-            if (usb_vcp_add(&vcp->info) != 0) {
+            if (!usb_vcp_add(&vcp->info)) {
                 usb_deinit();
                 mp_raise_msg(&mp_type_RuntimeError, "failed to add VCP interface");
             }
diff --git a/embed/extmod/modtrezorio/unix-msg-mock.h b/embed/extmod/modtrezorio/unix-msg-mock.h
index 9f19cabde5..96b47e643d 100644
--- a/embed/extmod/modtrezorio/unix-msg-mock.h
+++ b/embed/extmod/modtrezorio/unix-msg-mock.h
@@ -58,42 +58,34 @@ void usb_start(void) {
 void usb_stop(void) {
 }
 
-int usb_hid_add(const usb_hid_info_t *info) {
-    return 0;
+bool usb_hid_add(const usb_hid_info_t *info) {
+    return true;
 }
 
-int usb_vcp_add(const usb_vcp_info_t *info) {
-    return 0;
+bool usb_vcp_add(const usb_vcp_info_t *info) {
+    return true;
 }
 
-int usb_hid_can_read(uint8_t iface_num) {
+bool usb_hid_can_read(uint8_t iface_num) {
     if (iface_num != TREZOR_UDP_IFACE) {
-        return 0;
+        return false;
     }
     struct pollfd fds[] = {
         { sock, POLLIN, 0 },
     };
     int r = poll(fds, 1, 0);
-    if (r > 0) {
-        return 1;
-    } else {
-        return 0;
-    }
+    return r > 0;
 }
 
-int usb_hid_can_write(uint8_t iface_num) {
+bool usb_hid_can_write(uint8_t iface_num) {
     if (iface_num != TREZOR_UDP_IFACE) {
-        return 0;
+        return false;
     }
     struct pollfd fds[] = {
         { sock, POLLOUT, 0 },
     };
     int r = poll(fds, 1, 0);
-    if (r > 0) {
-        return 1;
-    } else {
-        return 0;
-    }
+    return r > 0;
 }
 
 int usb_hid_read(uint8_t iface_num, uint8_t *buf, uint32_t len) {
diff --git a/embed/trezorhal/usb_hid-defs.h b/embed/trezorhal/usb_hid-defs.h
index 4e74e8793b..3d6ce4993d 100644
--- a/embed/trezorhal/usb_hid-defs.h
+++ b/embed/trezorhal/usb_hid-defs.h
@@ -69,9 +69,9 @@ typedef struct {
     uint8_t ep_in_is_idle; // Set to 1 after IN endpoint gets idle
 } usb_hid_state_t;
 
-int usb_hid_add(const usb_hid_info_t *hid_info);
-int usb_hid_can_read(uint8_t iface_num);
-int usb_hid_can_write(uint8_t iface_num);
+bool usb_hid_add(const usb_hid_info_t *hid_info);
+bool usb_hid_can_read(uint8_t iface_num);
+bool usb_hid_can_write(uint8_t iface_num);
 int usb_hid_read(uint8_t iface_num, uint8_t *buf, uint32_t len);
 int usb_hid_write(uint8_t iface_num, const uint8_t *buf, uint32_t len);
 
diff --git a/embed/trezorhal/usb_hid-impl.h b/embed/trezorhal/usb_hid-impl.h
index 233af4f3fd..520d99ff09 100644
--- a/embed/trezorhal/usb_hid-impl.h
+++ b/embed/trezorhal/usb_hid-impl.h
@@ -17,34 +17,34 @@
 
 /* usb_hid_add adds and configures new USB HID interface according to
  * configuration options passed in `info`. */
-int usb_hid_add(const usb_hid_info_t *info) {
+bool usb_hid_add(const usb_hid_info_t *info) {
 
     usb_iface_t *iface = usb_get_iface(info->iface_num);
 
     if (iface == NULL) {
-        return 1; // Invalid interface number
+        return false; // Invalid interface number
     }
     if (iface->type != USB_IFACE_TYPE_DISABLED) {
-        return 1; // Interface is already enabled
+        return false; // Interface is already enabled
     }
 
     usb_hid_descriptor_block_t *d = usb_desc_alloc_iface(sizeof(usb_hid_descriptor_block_t));
 
     if (d == NULL) {
-        return 1; // Not enough space in the configuration descriptor
+        return false; // Not enough space in the configuration descriptor
     }
 
     if ((info->ep_in & USB_EP_DIR_MSK) != USB_EP_DIR_IN) {
-        return 1; // IN EP is invalid
+        return false; // IN EP is invalid
     }
     if ((info->ep_out & USB_EP_DIR_MSK) != USB_EP_DIR_OUT) {
-        return 1; // OUT EP is invalid
+        return false; // OUT EP is invalid
     }
     if (info->rx_buffer == NULL) {
-        return 1;
+        return false;
     }
     if (info->report_desc == NULL) {
-        return 1;
+        return false;
     }
 
     // Interface descriptor
@@ -101,41 +101,41 @@ int usb_hid_add(const usb_hid_info_t *info) {
     iface->hid.last_read_len   = 0;
     iface->hid.ep_in_is_idle   = 1;
 
-    return 0;
+    return true;
 }
 
-int usb_hid_can_read(uint8_t iface_num) {
+bool usb_hid_can_read(uint8_t iface_num) {
     usb_iface_t *iface = usb_get_iface(iface_num);
     if (iface == NULL) {
-        return 0; // Invalid interface number
+        return false; // Invalid interface number
     }
     if (iface->type != USB_IFACE_TYPE_HID) {
-        return 0; // Invalid interface type
+        return false; // Invalid interface type
     }
     if (iface->hid.last_read_len == 0) {
-        return 0; // Nothing in the receiving buffer
+        return false; // Nothing in the receiving buffer
     }
     if (usb_dev_handle.dev_state != USBD_STATE_CONFIGURED) {
-        return 0; // Device is not configured
+        return false; // Device is not configured
     }
-    return 1;
+    return true;
 }
 
-int usb_hid_can_write(uint8_t iface_num) {
+bool usb_hid_can_write(uint8_t iface_num) {
     usb_iface_t *iface = usb_get_iface(iface_num);
     if (iface == NULL) {
-        return 0; // Invalid interface number
+        return false; // Invalid interface number
     }
     if (iface->type != USB_IFACE_TYPE_HID) {
-        return 0; // Invalid interface type
+        return false; // Invalid interface type
     }
     if (iface->hid.ep_in_is_idle == 0) {
-        return 0; // Last transmission is not over yet
+        return false; // Last transmission is not over yet
     }
     if (usb_dev_handle.dev_state != USBD_STATE_CONFIGURED) {
-        return 0; // Device is not configured
+        return false; // Device is not configured
     }
-    return 1;
+    return true;
 }
 
 int usb_hid_read(uint8_t iface_num, uint8_t *buf, uint32_t len) {
@@ -216,7 +216,7 @@ int usb_hid_write_blocking(uint8_t iface_num, const uint8_t *buf, uint32_t len,
     return usb_hid_write(iface_num, buf, len);
 }
 
-static int usb_hid_class_init(USBD_HandleTypeDef *dev, usb_hid_state_t *state, uint8_t cfg_idx) {
+static void usb_hid_class_init(USBD_HandleTypeDef *dev, usb_hid_state_t *state, uint8_t cfg_idx) {
     // Open endpoints
     USBD_LL_OpenEP(dev, state->ep_in, USBD_EP_TYPE_INTR, state->max_packet_len);
     USBD_LL_OpenEP(dev, state->ep_out, USBD_EP_TYPE_INTR, state->max_packet_len);
@@ -230,16 +230,12 @@ static int usb_hid_class_init(USBD_HandleTypeDef *dev, usb_hid_state_t *state, u
 
     // Prepare the OUT EP to receive next packet
     USBD_LL_PrepareReceive(dev, state->ep_out, state->rx_buffer, state->max_packet_len);
-
-    return USBD_OK;
 }
 
-static int usb_hid_class_deinit(USBD_HandleTypeDef *dev, usb_hid_state_t *state, uint8_t cfg_idx) {
+static void usb_hid_class_deinit(USBD_HandleTypeDef *dev, usb_hid_state_t *state, uint8_t cfg_idx) {
     // Close endpoints
     USBD_LL_CloseEP(dev, state->ep_in);
     USBD_LL_CloseEP(dev, state->ep_out);
-
-    return USBD_OK;
 }
 
 static int usb_hid_class_setup(USBD_HandleTypeDef *dev, usb_hid_state_t *state, USBD_SetupReqTypedef *req) {
@@ -298,17 +294,17 @@ static int usb_hid_class_setup(USBD_HandleTypeDef *dev, usb_hid_state_t *state,
         }
         break;
     }
+
     return USBD_OK;
 }
 
-static uint8_t usb_hid_class_data_in(USBD_HandleTypeDef *dev, usb_hid_state_t *state, uint8_t ep_num) {
+static void usb_hid_class_data_in(USBD_HandleTypeDef *dev, usb_hid_state_t *state, uint8_t ep_num) {
     if ((ep_num | USB_EP_DIR_IN) == state->ep_in) {
         state->ep_in_is_idle = 1;
     }
-    return USBD_OK;
 }
 
-static uint8_t usb_hid_class_data_out(USBD_HandleTypeDef *dev, usb_hid_state_t *state, uint8_t ep_num) {
+static void usb_hid_class_data_out(USBD_HandleTypeDef *dev, usb_hid_state_t *state, uint8_t ep_num) {
     if (ep_num == state->ep_out) {
         state->last_read_len = USBD_LL_GetRxDataSize(dev, ep_num);
 
@@ -321,5 +317,4 @@ static uint8_t usb_hid_class_data_out(USBD_HandleTypeDef *dev, usb_hid_state_t *
             usb_ep_set_nak(dev, ep_num);
         }
     }
-    return USBD_OK;
 }
diff --git a/embed/trezorhal/usb_vcp-defs.h b/embed/trezorhal/usb_vcp-defs.h
index 83cc671bd5..6db7a52988 100644
--- a/embed/trezorhal/usb_vcp-defs.h
+++ b/embed/trezorhal/usb_vcp-defs.h
@@ -119,9 +119,9 @@ typedef struct {
     uint8_t ep_in_is_idle; // Set to 1 after IN endpoint gets idle
 } usb_vcp_state_t;
 
-int usb_vcp_add(const usb_vcp_info_t *vcp_info);
-int usb_vcp_can_read(uint8_t iface_num);
-int usb_vcp_can_write(uint8_t iface_num);
+bool usb_vcp_add(const usb_vcp_info_t *vcp_info);
+bool usb_vcp_can_read(uint8_t iface_num);
+bool usb_vcp_can_write(uint8_t iface_num);
 int usb_vcp_read(uint8_t iface_num, uint8_t *buf, uint32_t len);
 int usb_vcp_write(uint8_t iface_num, const uint8_t *buf, uint32_t len);
 
diff --git a/embed/trezorhal/usb_vcp-impl.h b/embed/trezorhal/usb_vcp-impl.h
index 34887ee5a5..e0b51605b5 100644
--- a/embed/trezorhal/usb_vcp-impl.h
+++ b/embed/trezorhal/usb_vcp-impl.h
@@ -42,49 +42,49 @@
 
 /* usb_vcp_add adds and configures new USB VCP interface according to
  * configuration options passed in `info`. */
-int usb_vcp_add(const usb_vcp_info_t *info) {
+bool usb_vcp_add(const usb_vcp_info_t *info) {
 
     usb_iface_t *iface = usb_get_iface(info->iface_num);
 
     if (iface == NULL) {
-        return 1; // Invalid interface number
+        return false; // Invalid interface number
     }
     if (iface->type != USB_IFACE_TYPE_DISABLED) {
-        return 1; // Interface is already enabled
+        return false; // Interface is already enabled
     }
 
     usb_vcp_descriptor_block_t *d = usb_desc_alloc_iface(sizeof(usb_vcp_descriptor_block_t));
 
     if (d == NULL) {
-        return 1; // Not enough space in the configuration descriptor
+        return false; // Not enough space in the configuration descriptor
     }
 
     if ((info->ep_cmd & USB_EP_DIR_MSK) != USB_EP_DIR_IN) {
-        return 1; // IN CMD EP is invalid
+        return false; // IN CMD EP is invalid
     }
     if ((info->ep_in & USB_EP_DIR_MSK) != USB_EP_DIR_IN) {
-        return 1; // IN EP is invalid
+        return false; // IN EP is invalid
     }
     if ((info->ep_out & USB_EP_DIR_MSK) != USB_EP_DIR_OUT) {
-        return 1; // OUT EP is invalid
+        return false; // OUT EP is invalid
     }
     if ((info->rx_buffer_len == 0) || (info->rx_buffer_len & (info->rx_buffer_len - 1)) != 0) {
-        return 1; // Capacity needs to be a power of 2
+        return false; // Capacity needs to be a power of 2
     }
     if ((info->tx_buffer_len == 0) || (info->tx_buffer_len & (info->tx_buffer_len - 1)) != 0) {
-        return 1; // Capacity needs to be a power of 2
+        return false; // Capacity needs to be a power of 2
     }
     if (info->rx_buffer == NULL) {
-        return 1;
+        return false;
     }
     if (info->rx_packet == NULL) {
-        return 1;
+        return false;
     }
     if (info->tx_buffer == NULL) {
-        return 1;
+        return false;
     }
     if (info->tx_packet == NULL) {
-        return 1;
+        return false;
     }
 
     // Interface association descriptor
@@ -205,7 +205,7 @@ int usb_vcp_add(const usb_vcp_info_t *info) {
 
     iface->vcp.ep_in_is_idle = 1;
 
-    return 0;
+    return true;
 }
 
 static inline size_t ring_length(usb_rbuf_t *b) {
@@ -220,32 +220,32 @@ static inline int ring_full(usb_rbuf_t *b) {
     return ring_length(b) == b->cap;
 }
 
-int usb_vcp_can_read(uint8_t iface_num) {
+bool usb_vcp_can_read(uint8_t iface_num) {
     usb_iface_t *iface = usb_get_iface(iface_num);
     if (iface == NULL) {
-        return 0; // Invalid interface number
+        return false; // Invalid interface number
     }
     if (iface->type != USB_IFACE_TYPE_VCP) {
-        return 0; // Invalid interface type
+        return false; // Invalid interface type
     }
     if (ring_empty(&iface->vcp.rx_ring)) {
-        return 0; // Nothing in the rx buffer
+        return false; // Nothing in the rx buffer
     }
-    return 1;
+    return true;
 }
 
-int usb_vcp_can_write(uint8_t iface_num) {
+bool usb_vcp_can_write(uint8_t iface_num) {
     usb_iface_t *iface = usb_get_iface(iface_num);
     if (iface == NULL) {
-        return 0; // Invalid interface number
+        return false; // Invalid interface number
     }
     if (iface->type != USB_IFACE_TYPE_VCP) {
-        return 0; // Invalid interface type
+        return false; // Invalid interface type
     }
     if (ring_full(&iface->vcp.tx_ring)) {
-        return 0; // Tx ring buffer is full
+        return false; // Tx ring buffer is full
     }
-    return 1;
+    return true;
 }
 
 int usb_vcp_read(uint8_t iface_num, uint8_t *buf, uint32_t len) {
@@ -313,7 +313,7 @@ int usb_vcp_write_blocking(uint8_t iface_num, const uint8_t *buf, uint32_t len,
     return usb_vcp_write(iface_num, buf, len);
 }
 
-static int usb_vcp_class_init(USBD_HandleTypeDef *dev, usb_vcp_state_t *state, uint8_t cfg_idx) {
+static void usb_vcp_class_init(USBD_HandleTypeDef *dev, usb_vcp_state_t *state, uint8_t cfg_idx) {
     // Open endpoints
     USBD_LL_OpenEP(dev, state->ep_in, USBD_EP_TYPE_BULK,  state->max_packet_len);
     USBD_LL_OpenEP(dev, state->ep_out, USBD_EP_TYPE_BULK, state->max_packet_len);
@@ -328,17 +328,13 @@ static int usb_vcp_class_init(USBD_HandleTypeDef *dev, usb_vcp_state_t *state, u
 
     // Prepare the OUT EP to receive next packet
     USBD_LL_PrepareReceive(dev, state->ep_out, state->rx_packet, state->max_packet_len);
-
-    return USBD_OK;
 }
 
-static int usb_vcp_class_deinit(USBD_HandleTypeDef *dev, usb_vcp_state_t *state, uint8_t cfg_idx) {
+static void usb_vcp_class_deinit(USBD_HandleTypeDef *dev, usb_vcp_state_t *state, uint8_t cfg_idx) {
     // Close endpoints
     USBD_LL_CloseEP(dev, state->ep_in);
     USBD_LL_CloseEP(dev, state->ep_out);
     USBD_LL_CloseEP(dev, state->ep_cmd);
-
-    return USBD_OK;
 }
 
 static int usb_vcp_class_setup(USBD_HandleTypeDef *dev, usb_vcp_state_t *state, USBD_SetupReqTypedef *req) {
@@ -377,14 +373,13 @@ static int usb_vcp_class_setup(USBD_HandleTypeDef *dev, usb_vcp_state_t *state,
     return USBD_OK;
 }
 
-static uint8_t usb_vcp_class_data_in(USBD_HandleTypeDef *dev, usb_vcp_state_t *state, uint8_t ep_num) {
+static void usb_vcp_class_data_in(USBD_HandleTypeDef *dev, usb_vcp_state_t *state, uint8_t ep_num) {
     if ((ep_num | USB_EP_DIR_IN) == state->ep_in) {
         state->ep_in_is_idle = 1;
     }
-    return USBD_OK;
 }
 
-static uint8_t usb_vcp_class_data_out(USBD_HandleTypeDef *dev, usb_vcp_state_t *state, uint8_t ep_num) {
+static void usb_vcp_class_data_out(USBD_HandleTypeDef *dev, usb_vcp_state_t *state, uint8_t ep_num) {
     if (ep_num == state->ep_out) {
         uint32_t len = USBD_LL_GetRxDataSize(dev, ep_num);
 
@@ -407,12 +402,11 @@ static uint8_t usb_vcp_class_data_out(USBD_HandleTypeDef *dev, usb_vcp_state_t *
         // Prepare the OUT EP to receive next packet
         USBD_LL_PrepareReceive(dev, state->ep_out, state->rx_packet, state->max_packet_len);
     }
-    return USBD_OK;
 }
 
-static uint8_t usb_vcp_class_sof(USBD_HandleTypeDef *dev, usb_vcp_state_t *state) {
+static void usb_vcp_class_sof(USBD_HandleTypeDef *dev, usb_vcp_state_t *state) {
     if (!state->ep_in_is_idle) {
-        return USBD_OK;
+        return;
     }
 
     // Read from the tx ring buffer
@@ -432,6 +426,4 @@ static uint8_t usb_vcp_class_sof(USBD_HandleTypeDef *dev, usb_vcp_state_t *state
         state->ep_in_is_idle = 0;
         USBD_LL_Transmit(&usb_dev_handle, state->ep_in, buf, (uint16_t)i);
     }
-
-    return USBD_OK;
 }