bsp/leon3: Improve printk() support

Use the idle stack to buffer early uses of printk().  Print the buffered
characters during initialization when the UART is available and before
the idle stack is used normally.

This fix relates to a Coverity issue (PW.SET_BUT_NOT_USED).

bsps/sparc/leon3/console/printk_support.c

@@ -19,18 +19,44 @@
 #include <leon.h>
 #include <rtems/bspIo.h>
 #include <rtems/sysinit.h>
+#include <rtems/score/thread.h>
 #include <grlib/apbuart.h>
 
 int leon3_debug_uart_index __attribute__((weak)) = 0;
 struct apbuart_regs *leon3_debug_uart = NULL;
 
-/* Before UART driver has registered (or when no UART is available), calls to
+/*
- * printk that gets to bsp_out_char() will be filling data into the
+ * Before UART driver is available, use the idle stack to buffer early uses of
- * pre_printk_dbgbuf[] buffer, hopefully the buffer can help debugging the
+ * printk().
- * early BSP boot.. At least the last printk() will be caught.
  */
-static char pre_printk_dbgbuf[32] = {0};
+static size_t bsp_debug_uart_pre_init_buf_index;
-static int pre_printk_pos = 0;
+
+static void bsp_debug_uart_pre_init_out(char c)
+{
+  size_t i;
+
+  i = bsp_debug_uart_pre_init_buf_index;
+
+  if (i < _Thread_Idle_stack_size) {
+    bsp_debug_uart_pre_init_buf_index = i + 1;
+    _Thread_Idle_stacks[i] = c;
+  }
+}
+
+static void bsp_debug_uart_discard(char c)
+{
+  (void) c;
+}
+
+static void bsp_debug_uart_output_char(char c)
+{
+  apbuart_outbyte_polled(leon3_debug_uart, c, 1, 1);
+}
+
+static int bsp_debug_uart_poll_char(void)
+{
+  return apbuart_inbyte_nonblocking(leon3_debug_uart);
+}
 
 /* Initialize the BSP system debug console layer. It will scan AMBA Plu&Play
  * for a debug APBUART and enable RX/TX for that UART.
@@ -62,14 +88,29 @@ static void bsp_debug_uart_init(void)
   adev = (void *)ambapp_for_each(&ambapp_plb, (OPTIONS_ALL|OPTIONS_APB_SLVS),
                                  VENDOR_GAISLER, GAISLER_APBUART,
                                  ambapp_find_by_idx, (void *)&i);
-  if (adev) {
+  if (adev != NULL) {
-    /* Found a matching debug console, initialize debug uart if present
+    size_t i;
-     * for printk
+    size_t n;
+
+    /*
+     * Found a matching debug console, initialize debug UART if present for
+     * printk().
      */
     apb = (struct ambapp_apb_info *)adev->devinfo;
     leon3_debug_uart = (struct apbuart_regs *)apb->start;
     leon3_debug_uart->ctrl |= APBUART_CTRL_RE | APBUART_CTRL_TE;
     leon3_debug_uart->status = 0;
+
+    BSP_poll_char = bsp_debug_uart_poll_char;
+    BSP_output_char = bsp_debug_uart_output_char;
+
+    n = bsp_debug_uart_pre_init_buf_index;
+
+    for (i = 0; i < n; ++i) {
+      rtems_putc(_Thread_Idle_stacks[i]);
+    }
+  } else {
+    BSP_output_char = bsp_debug_uart_discard;
   }
 }
 
@@ -79,35 +120,6 @@ RTEMS_SYSINIT_ITEM(
   RTEMS_SYSINIT_ORDER_FOURTH
 );
 
-/* putchar/getchar for printk */
+BSP_output_char_function_type BSP_output_char = bsp_debug_uart_pre_init_out;
-static void bsp_out_char(char c)
-{
-  if (leon3_debug_uart == NULL) {
-    /* Local debug buffer when UART driver has not registered */
-    pre_printk_dbgbuf[pre_printk_pos++] = c;
-    pre_printk_pos = pre_printk_pos & (sizeof(pre_printk_dbgbuf)-1);
-    return;
-  }
 
-  apbuart_outbyte_polled(leon3_debug_uart, c, 1, 1);
+BSP_polling_getchar_function_type BSP_poll_char;
-}
-
-/*
- *  To support printk
- */
-
-BSP_output_char_function_type BSP_output_char = bsp_out_char;
-
-static int bsp_in_char(void)
-{
-  int tmp;
-
-  if (leon3_debug_uart == NULL)
-    return -1;
-
-  while ((tmp = apbuart_inbyte_nonblocking(leon3_debug_uart)) < 0)
-    ;
-  return tmp;
-}
-
-BSP_polling_getchar_function_type BSP_poll_char = bsp_in_char;