[PATCH] console: flush consoles on newline when debugging

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

For debugging hangs, CONFIG_DEBUG_PROBES and CONFIG_DEBUG_INITCALLS are
useful tools to pinpoint where the issue is. FOr issues that lock up the
SoC, their output can be misleading if we have bigger UART FIFO and not
all output has managed to make it out.

Add a new DEBUG_FLUSH_LINE_BREAK to make debugging this easier.
The option is unnecessary outside of debugging, so for now we don't add
a prompt by default and select it as needed.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
 common/Kconfig   | 12 ++++++++++++
 common/console.c |  5 ++++-
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/common/Kconfig b/common/Kconfig
index 33903aa249b7..6c0de894faf5 100644
--- a/common/Kconfig
+++ b/common/Kconfig
@@ -1703,8 +1703,19 @@ config DEBUG_AT91_UART_BASE
 	  Specify UART port base address on which barebox low-level
 	  debug messages should be output.
 
+config DEBUG_FLUSH_LINE_BREAK
+	bool "Flush consoles on new line" if COMPILE_TEST
+	help
+	  Many serial drivers configure and use hardware FIFOs as not to
+	  delay the boot. When debuging some king of bugs, such as clock
+	  issues that hang the SoC, this can falsify debugging output,
+	  because the UART doesn't output a submitted message fully, before
+	  the SoC hangs. This option will flush serial FIFOs when processing
+	  the new line feed characters.
+
 config DEBUG_INITCALLS
 	bool "Trace initcalls"
+	select DEBUG_FLUSH_LINE_BREAK
 	help
 	  If enabled this will print initcall traces.
 
@@ -1719,6 +1730,7 @@ config DEBUG_PBL
 
 config DEBUG_PROBES
 	bool "Trace driver probes/removes"
+	select DEBUG_FLUSH_LINE_BREAK
 	help
 	  If enabled this will log driver probe and remove traces. If DEBUG_LL is enabled,
 	  probes will be printed even before registering consoles. If it's disabled, they
diff --git a/common/console.c b/common/console.c
index 03b76b122b2b..9ca92a74a8f3 100644
--- a/common/console.c
+++ b/common/console.c
@@ -277,8 +277,11 @@ static int __console_puts(struct console_device *cdev, const char *s,
 	size_t i;
 
 	for (i = 0; i < nbytes; i++) {
-		if (*s == '\n')
+		if (*s == '\n') {
 			cdev->putc(cdev, '\r');
+			if (IS_ENABLED(CONFIG_DEBUG_FLUSH_LINE_BREAK) && cdev->flush)
+				cdev->flush(cdev);
+		}
 
 		cdev->putc(cdev, *s);
 		s++;
-- 
2.39.2