linux-kernel - [PATCH] serial: uartps: Wait for tx

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Date:   Tue,  7 Apr 2020 22:23:11 +0530
From:   Raviteja Narayanam <raviteja.narayanam@...inx.com>
To:     linux-serial@...r.kernel.org
Cc:     gregkh@...uxfoundation.org, jslaby@...e.com,
        michal.simek@...inx.com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, git@...inx.com,
        Raviteja Narayanam <raviteja.narayanam@...inx.com>
Subject: [PATCH] serial: uartps: Wait for tx_empty in console setup

On some platforms, the log is corrupted while console is being
registered. It is observed that when set_termios is called, there
are still some bytes in the FIFO to be transmitted.

So, wait for tx_empty inside cdns_uart_console_setup before
calling set_termios.

Signed-off-by: Raviteja Narayanam <raviteja.narayanam@...inx.com>
---
 drivers/tty/serial/xilinx_uartps.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c
index 6b26f76..23468ff 100644
--- a/drivers/tty/serial/xilinx_uartps.c
+++ b/drivers/tty/serial/xilinx_uartps.c
@@ -1260,6 +1260,8 @@ static int cdns_uart_console_setup(struct console *co, char *options)
 	int bits = 8;
 	int parity = 'n';
 	int flow = 'n';
+	unsigned long time_out = jiffies + usecs_to_jiffies(TX_TIMEOUT);
+	int status;
 
 	if (!port->membase) {
 		pr_debug("console on " CDNS_UART_TTY_NAME "%i not present\n",
@@ -1270,6 +1272,14 @@ static int cdns_uart_console_setup(struct console *co, char *options)
 	if (options)
 		uart_parse_options(options, &baud, &parity, &bits, &flow);
 
+	/* Wait for tx_empty before setting up the console */
+	while (time_before(jiffies, time_out)) {
+		status = cdns_uart_tx_empty(port);
+		if (status == TIOCSER_TEMT)
+			break;
+		cpu_relax();
+	}
+
 	return uart_set_options(port, co, baud, parity, bits, flow);
 }
 #endif /* CONFIG_SERIAL_XILINX_PS_UART_CONSOLE */
-- 
2.7.4