serial: 8250_dw: Store LSR into lsr_saved_flags in dw8250_tx_wait_empty()

BugLink: https://bugs.launchpad.net/bugs/1990162
[ Upstream commit af14f3007e2dca0d112f10f6717ba43093f74e81 ]

Make sure LSR flags are preserved in dw8250_tx_wait_empty(). This
function is called from a low-level out function and therefore cannot
call serial_lsr_in() as it would lead to infinite recursion.

It is borderline if the flags need to be saved here at all since this
code relates to writing LCR register which usually implies no important
characters should be arriving.

Fixes: 914eaf935ec7 ("serial: 8250_dw: Allow TX FIFO to drain before writing to UART_LCR")
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20220608095431.18376-7-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index 49559731bbcf1cf595fef5b787d528afa513889c..ace221afeb039b02295fa6b2563bc7228bbad79e 100644 (file)
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -124,12 +124,15 @@ static void dw8250_check_lcr(struct uart_port *p, int value)
 /* Returns once the transmitter is empty or we run out of retries */
 static void dw8250_tx_wait_empty(struct uart_port *p)
 {
+       struct uart_8250_port *up = up_to_u8250p(p);
        unsigned int tries = 20000;
        unsigned int delay_threshold = tries - 1000;
        unsigned int lsr;
 
        while (tries--) {
                lsr = readb (p->membase + (UART_LSR << p->regshift));
+               up->lsr_saved_flags |= lsr & LSR_SAVE_FLAGS;
+
                if (lsr & UART_LSR_TEMT)
                        break;