Commit 0c6cfc10 authored Dec 23, 2020 by Pali Rohár Committed by Greg Kroah-Hartman Jan 27, 2021

serial: mvebu-uart: fix tx lost characters at power off



commit 54ca955b5a4024e2ce0f206b03adb7109bc4da26 upstream.

Commit c685af11 ("serial: mvebu-uart: fix tx lost characters") fixed tx
lost characters at low baud rates but started causing tx lost characters
when kernel is going to power off or reboot.

TX_EMP tells us when transmit queue is empty therefore all characters were
transmitted. TX_RDY tells us when CPU can send a new character.

Therefore we need to use different check prior transmitting new character
and different check after all characters were sent.

This patch splits polling code into two functions: wait_for_xmitr() which
waits for TX_RDY and wait_for_xmite() which waits for TX_EMP.

When rebooting A3720 platform without this patch on UART is print only:
[   42.699�

And with this patch on UART is full output:
[   39.530216] reboot: Restarting system

Fixes: c685af11 ("serial: mvebu-uart: fix tx lost characters")
Signed-off-by: Pali Rohár <pali@kernel.org>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20201223191931.18343-1-pali@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 0f53a6b4

drivers/tty/serial/mvebu-uart.c

+9 −1

Original line number	Diff line number	Diff line
		@@ -637,6 +637,14 @@ static void wait_for_xmitr(struct uart_port *port)
		(val & STAT_TX_RDY(port)), 1, 10000);
		}

		static void wait_for_xmite(struct uart_port *port)
		{
		u32 val;

		readl_poll_timeout_atomic(port->membase + UART_STAT, val,
		(val & STAT_TX_EMP), 1, 10000);
		}

		static void mvebu_uart_console_putchar(struct uart_port *port, int ch)
		{
		wait_for_xmitr(port);
		@@ -664,7 +672,7 @@ static void mvebu_uart_console_write(struct console co, const char s,

		uart_console_write(port, s, count, mvebu_uart_console_putchar);

		wait_for_xmitr(port);
		wait_for_xmite(port);

		if (ier)
		writel(ier, port->membase + UART_CTRL(port));