From 5e998b4de33fed22da29e3a12e2856f9c00eaebc Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Pali=20Roh=C3=A1r?= Date: Thu, 23 Jun 2022 14:13:56 +0200 Subject: [PATCH] serial: ns16550: Wait in debug_uart_init until tx buffer is empty MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Commit d293759d55cc ("serial: ns16550: Add support for SPL_DEBUG_UART_BASE") fixed support for setting correct early debug UART base address in SPL. But after this commit, output from Marvell A385 BootROM is truncated or lost and not fully present on serial console. Debugging this issue showed that BootROM just put bytes into UART HW output buffer and does not wait until UART HW transmit all characters. U-Boot ns16550 early debug is initialized very early and during its initialization is resetting UART HW and flushing remaining transmit buffer (which still contains BootROM output). Fix this issue by waiting in init function prior resetting UART HW until TxEmpty bit in UART Line Status Register is set. TxEmpty is set when all remaining bytes from HW buffer are transmitted. Signed-off-by: Pali Rohár Reviewed-by: Stefan Roese [trini: Add comment, move ';' to new line per checkpatch.pl] Signed-off-by: Tom Rini --- drivers/serial/ns16550.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/serial/ns16550.c b/drivers/serial/ns16550.c index 78bfe6281c..47bad6f8e2 100644 --- a/drivers/serial/ns16550.c +++ b/drivers/serial/ns16550.c @@ -328,6 +328,10 @@ static inline void _debug_uart_init(void) struct ns16550 *com_port = (struct ns16550 *)CONFIG_VAL(DEBUG_UART_BASE); int baud_divisor; + /* Wait until tx buffer is empty */ + while (!(serial_din(&com_port->lsr) & UART_LSR_TEMT)) + ; + /* * We copy the code from above because it is already horribly messy. * Trying to refactor to nicely remove the duplication doesn't seem