esp_rom: add patch to set USB device serial descriptor to MAC address

components/esp_rom/CMakeLists.txt

@@ -2,7 +2,8 @@ idf_build_get_property(target IDF_TARGET)
 
 idf_component_register(SRCS "patches/esp_rom_crc.c"
                        INCLUDE_DIRS include
-                       PRIV_INCLUDE_DIRS "${target}")
+                       PRIV_INCLUDE_DIRS "${target}"
+                       PRIV_REQUIRES soc)
 
 if(BOOTLOADER_BUILD)
     set(scripts
@@ -83,3 +84,7 @@ else() # Regular app build
     target_linker_script(${COMPONENT_LIB} INTERFACE "${scripts}")
 
 endif()
+
+if(target STREQUAL "esp32s2")
+    target_sources(${COMPONENT_LIB} PRIVATE "esp32s2/usb_descriptors.c")
+endif()

components/esp_rom/esp32s2/usb_descriptors.c

@@ -0,0 +1,75 @@
+// Copyright 2020 Espressif Systems (Shanghai) PTE LTD
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <string.h>
+#include "esp32s2/rom/usb/usb_common.h"
+#include "soc/soc.h"
+#include "soc/efuse_reg.h"
+
+/* USB CDC descriptor.
+ * Note that we aren't using the one in ROM since it doesn't
+ * set "serial" to the MAC address.
+ * However overriding the descriptor is cheap - we can reuse most
+ * of its components from ROM.
+ */
+
+/* This is not const, since the MAC address is only known at run time */
+static struct string_descriptor s_str_serial_descr = {
+    .bLength = 2 + 2 * 17,
+    .bDescriptorType = 0x03,
+    .bString={'0', '0', ':', '0', '0', ':', '0', '0', ':', '0', '0', ':', '0', '0', ':', '0', '0'}
+};
+
+static const struct rom_usb_descriptors s_acm_usb_descriptors_override = {
+    .device_descr = &general_device_descr,
+    .config_descr = { &acm_config_descr },
+    .string_count = 4,
+    .string0_descr = &string0_descr,
+    .string_descrs = {
+        &str_manu_descr,
+        &str_prod_descr,
+        &s_str_serial_descr
+    }
+};
+
+static inline uint16_t nibble_to_hex_u16(uint8_t b)
+{
+    if (b < 0xa) {
+        return '0' + b;
+    } else {
+        return 'a' + b - 0xa;
+    }
+}
+
+void rom_usb_cdc_set_descriptor_patch(void)
+{
+    /* Get the MAC address */
+    const uint32_t mac0 = REG_GET_FIELD(EFUSE_RD_MAC_SPI_SYS_0_REG, EFUSE_MAC_0);
+    const uint32_t mac1 = REG_GET_FIELD(EFUSE_RD_MAC_SPI_SYS_1_REG, EFUSE_MAC_1);
+    uint8_t mac_bytes[6];
+    memcpy(mac_bytes, &mac0, 4);
+    memcpy(mac_bytes + 4, &mac1, 2);
+
+    /* Convert to UTF16 string */
+    uint16_t* dst = s_str_serial_descr.bString;
+    for (int i = 0; i < 6; ++i) {
+        uint8_t b = mac_bytes[5 - i]; /* printing from the MSB */
+        *dst++ = nibble_to_hex_u16(b >> 4);
+        *dst++ = nibble_to_hex_u16(b & 0xf);
+        dst++;
+    }
+
+    /* Override the pointer to descriptors structure */
+    rom_usb_curr_desc = &s_acm_usb_descriptors_override;
+}

components/esp_rom/include/esp32s2/rom/usb/usb_common.h

@@ -238,6 +238,11 @@ extern const struct rom_usb_descriptors acm_usb_descriptors;
 extern const struct rom_usb_descriptors dfu_usb_descriptors;
 extern const struct rom_usb_descriptors *rom_usb_curr_desc;
 
+/* ROM patch: set the ACM descriptor with the correct serial number.
+ * Only needed on ESP32-S2, on later chips the ROM descriptor is correct.
+ */
+void rom_usb_cdc_set_descriptor_patch(void);
+
 
 #ifdef __cplusplus
 }