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

Commit c685af1108 ("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: c685af1108 ("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>
master
Pali Rohár 2020-12-23 20:19:31 +01:00 committed by Greg Kroah-Hartman
parent 5c8fe583cc
commit 54ca955b5a
1 changed files with 9 additions and 1 deletions
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10
drivers/tty/serial/mvebu-uart.c
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@ -648,6 +648,14 @@ 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);
@ -675,7 +683,7 @@ 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));