tcp client using ESP32 and ATSAME(main MCU) with lwIP

I interfaced ethernet and GPRS module with ATSAME53N20A MCU to access internet using lwIP and its working.

I also used ready to use esp-idf examples to create tcpip_client in eclipse with ESP32(standalone) and it is working as well.

Now, I want to make a tcpip_client(lwIP netconn) using ESP32 module together with ATSAME53. ATSAME will be acting as the main MCU and I want to create a client using netconn APIs in lwip which will be in ATSAME. ESP32 uart pins connected to uart pins in ATSAME. I want ESP32 to be just bridge and give data from the router(internet) to ATSAME which will use lwip to process it and create a netconn client.

My theory:
(ESP-->ATSAME)
I changed inside wlanif_input(struct netif *netif, void *buffer, u16_t len, void* eb) function in ESPlwip and send the buffer(packet) to ATSAME using uart(instead of tcpip_thread to process). I want packets to be processed in ATSAMElwip. When I received packets from ESP32 in ATSAME side, I called tcpip_input(p, &TCPIP_STACK_INTERFACE_0_desc) to send it to tcpip_thread to be processed.

(ATSAME-->ESP)
Coming packets from ATSAMElwip were sent to esp using tcpip_output_raw (I created it and called from TCPIP_STACK_INTERFACE_0_stack_init fn) and received in ESP using low_level_output function and sent using esp_wifi_internal_tx(wifi_if, q->payload, q->len);

Are you using the ESP32 with the LUA script or any other interpreted command language, or have you compiled some C code directly from SDK to run within it? I fear that the Serial interface, unless being interrupt driven, will be a bootleneck; Anyway, even the lowest standard Ethernet speed 10Mbps would traffic data far above the maximum standard UART baud rate, typically 115.2Kbps.

I am using ESP32 with eclipse IDE with C and ATSAME with atmel studio IDE with C. I wıll be using uart with 921600 baudrate. I hope it will be enough. Thank you