driver: serial: gd32: missing `irq_update` in `usart_gd32_driver_api`

[chang196700]

Describe the bug In the file drivers/serial/usart_gd32.c, the usart_gd32_driver_api is missing the irq_update function implementation. As a result, some functions such as modem_backend_uart_isr_irq_handler (subsys/modem/backends/modem_backend_uart_isr.c#L93) cannot be executed as expected

Expected behavior Implement irq_update,

Impact Cannot use modem_backend_uart with gd32 serial driver.

Environment (please complete the following information):

• OS: Windows
• Toolchain Zephyr SDK
• Commit SHA used 14642091730b26abf49e9ca359fe993ac8f56137

Additional context https://github.com/zephyrproject-rtos/zephyr/blob/14642091730b26abf49e9ca359fe993ac8f56137/drivers/serial/usart_gd32.c#L281

https://github.com/zephyrproject-rtos/zephyr/blob/14642091730b26abf49e9ca359fe993ac8f56137/subsys/modem/backends/modem_backend_uart_isr.c#L93

[cameled]

@chang196700 Looks stm32 return a constant 1, can you help to try below patch?

diff --git a/drivers/serial/usart_gd32.c b/drivers/serial/usart_gd32.c
index 22bf9fb31b8..6eeb38202bc 100644
--- a/drivers/serial/usart_gd32.c
+++ b/drivers/serial/usart_gd32.c
@@ -267,6 +267,12 @@ int usart_gd32_irq_is_pending(const struct device *dev)
         usart_interrupt_flag_get(cfg->reg, USART_INT_FLAG_TC)));
 }

+static int usart_gd32_irq_update(const struct device *dev)
+{
+   ARG_UNUSED(dev);
+   return 1;
+}
+
 void usart_gd32_irq_callback_set(const struct device *dev,
                 uart_irq_callback_user_data_t cb,
                 void *user_data)
@@ -295,6 +301,7 @@ static const struct uart_driver_api usart_gd32_driver_api = {
    .irq_err_enable = usart_gd32_irq_err_enable,
    .irq_err_disable = usart_gd32_irq_err_disable,
    .irq_is_pending = usart_gd32_irq_is_pending,
+   .irq_update = usart_gd32_irq_update,
    .irq_callback_set = usart_gd32_irq_callback_set,
 #endif /* CONFIG_UART_INTERRUPT_DRIVEN */
 };

[chang196700]

@cameled ok, I'll try it.