From: Pali Rohár pali@kernel.org
commit 54ca955b5a4024e2ce0f206b03adb7109bc4da26 upstream.
Commit c685af1108d7 ("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: c685af1108d7 ("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
--- drivers/tty/serial/mvebu-uart.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)
--- a/drivers/tty/serial/mvebu-uart.c +++ b/drivers/tty/serial/mvebu-uart.c @@ -637,6 +637,14 @@ static void wait_for_xmitr(struct uart_p (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(str
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));