From be03b0651ffd8bab69dfd574c6818b446c0753ce Mon Sep 17 00:00:00 2001 From: =?utf8?q?Ilpo=20J=C3=A4rvinen?= Date: Fri, 20 May 2022 13:35:41 +0300 Subject: [PATCH] serial: 8250: Store to lsr_save_flags after lsr read MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 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") Cc: stable Acked-by: Uwe Kleine-König Signed-off-by: Uwe Kleine-König Signed-off-by: Ilpo Järvinen Link: https://lore.kernel.org/r/f4d774be-1437-a550-8334-19d8722ab98c@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 78b6ded..8f32fe9 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -1517,6 +1517,8 @@ 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; /* -- 2.7.4