uart: Add missing critical section wrappers around rx_buffered_len

The missing barriers caused uart_get_buffered_data_len() to (very rarely)
return a garbage value. When used in MicroPython, though, this caused
select() to return and a subsequent read() to stall indefinitely until
a char was actually available.

Signed-off-by: Chen Yi Qun <[email protected]>

Closes #6397
Merges #6396

Author: o-marshmallow

components/driver/uart.c

@@ -257,7 +257,9 @@ esp_err_t uart_set_stop_bits(uart_port_t uart_num, uart_stop_bits_t stop_bit)
 esp_err_t uart_get_stop_bits(uart_port_t uart_num, uart_stop_bits_t* stop_bit)
 {
     UART_CHECK((uart_num < UART_NUM_MAX), "uart_num error", ESP_FAIL);
+    UART_ENTER_CRITICAL(&(uart_context[uart_num].spinlock));
     uart_hal_get_stop_bits(&(uart_context[uart_num].hal), stop_bit);
+    UART_EXIT_CRITICAL(&(uart_context[uart_num].spinlock));
     return ESP_OK;
 }
 
@@ -273,7 +275,9 @@ esp_err_t uart_set_parity(uart_port_t uart_num, uart_parity_t parity_mode)
 esp_err_t uart_get_parity(uart_port_t uart_num, uart_parity_t* parity_mode)
 {
     UART_CHECK((uart_num < UART_NUM_MAX), "uart_num error", ESP_FAIL);
+    UART_ENTER_CRITICAL(&(uart_context[uart_num].spinlock));
     uart_hal_get_parity(&(uart_context[uart_num].hal), parity_mode);
+    UART_EXIT_CRITICAL(&(uart_context[uart_num].spinlock));
     return ESP_OK;
 }
 
@@ -1262,7 +1266,9 @@ esp_err_t uart_get_buffered_data_len(uart_port_t uart_num, size_t* size)
 {
     UART_CHECK((uart_num < UART_NUM_MAX), "uart_num error", ESP_FAIL);
     UART_CHECK((p_uart_obj[uart_num]), "uart driver error", ESP_FAIL);
+    UART_ENTER_CRITICAL(&(uart_context[uart_num].spinlock));
     *size = p_uart_obj[uart_num]->rx_buffered_len;
+    UART_EXIT_CRITICAL(&(uart_context[uart_num].spinlock));
     return ESP_OK;
 }
 
@@ -1303,14 +1309,19 @@ esp_err_t uart_flush_input(uart_port_t uart_num)
         }
         data = (uint8_t*) xRingbufferReceive(p_uart->rx_ring_buf, &size, (portTickType) 0);
         if(data == NULL) {
+            bool error = false;
+            UART_ENTER_CRITICAL(&(uart_context[uart_num].spinlock));
             if( p_uart_obj[uart_num]->rx_buffered_len != 0 ) {
-                ESP_LOGE(UART_TAG, "rx_buffered_len error");
                 p_uart_obj[uart_num]->rx_buffered_len = 0;
+                error = true;
             }
             //We also need to clear the `rx_buffer_full_flg` here.
-            UART_ENTER_CRITICAL(&(uart_context[uart_num].spinlock));
             p_uart_obj[uart_num]->rx_buffer_full_flg = false;
             UART_EXIT_CRITICAL(&(uart_context[uart_num].spinlock));
+            if (error) {
+                // this must be called outside the critical section
+                ESP_LOGE(UART_TAG, "rx_buffered_len error");
+            }
             break;
         }
         UART_ENTER_CRITICAL(&(uart_context[uart_num].spinlock));