From ce338e4477cfdff0abeb27eff2d43fc379ee9ebb Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= Date: Wed, 8 Jun 2022 12:54:26 +0300 Subject: [PATCH] serial: 8250: Store to lsr_save_flags after lsr read MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Not all LSR register flags are preserved across reads. Therefore, LSR readers must store the non-preserved bits into lsr_save_flags. This fix was initially mixed into feature commit f6f586102add ("serial: 8250: Handle UART without interrupt on TEMT using em485"). However, that feature change had a flaw and it was reverted to make room for simpler approach providing the same feature. The embedded fix got reverted with the feature change. Re-add the lsr_save_flags fix and properly mark it's a fix. Link: https://lore.kernel.org/all/1d6c31d-d194-9e6a-ddf9-5f29af829f3@linux.intel.com/T/#m1737eef986bd20cf19593e344cebd7b0244945fc Fixes: e490c9144cfa ("tty: Add software emulated RS485 support for 8250") Co-developed-by: Uwe Kleine-König Reviewed-by: Andy Shevchenko Signed-off-by: Uwe Kleine-König Signed-off-by: Ilpo Järvinen Link: https://lore.kernel.org/r/20220608095431.18376-2-ilpo.jarvinen@linux.intel.com Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/8250/8250_port.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index a3ffbdfe8fae..209ecb1f29ed 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -1511,6 +1511,8 @@ static inline void __stop_tx(struct uart_8250_port *p) unsigned char lsr = serial_in(p, UART_LSR); u64 stop_delay = 0; + p->lsr_saved_flags |= lsr & LSR_SAVE_FLAGS; + if (!(lsr & UART_LSR_THRE)) return; /*