[PATCH 4.19 219/293] serial: sh-sci: fix break handling for sysrq

From: Greg Kroah-Hartman
Date: Mon Sep 20 2021 - 13:55:18 EST


From: Ulrich Hecht <uli+renesas@xxxxxxxx>

[ Upstream commit 87b8061bad9bd4b549b2daf36ffbaa57be2789a2 ]

This fixes two issues that cause the sysrq sequence to be inadvertently
aborted on SCIF serial consoles:

- a NUL character remains in the RX queue after a break has been detected,
which is then passed on to uart_handle_sysrq_char()
- the break interrupt is handled twice on controllers with multiplexed ERI
and BRI interrupts

Signed-off-by: Ulrich Hecht <uli+renesas@xxxxxxxx>
Link: https://lore.kernel.org/r/20210816162201.28801-1-uli+renesas@xxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
drivers/tty/serial/sh-sci.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
index db5b11879910..6f44c5f0ef3a 100644
--- a/drivers/tty/serial/sh-sci.c
+++ b/drivers/tty/serial/sh-sci.c
@@ -1750,6 +1750,10 @@ static irqreturn_t sci_br_interrupt(int irq, void *ptr)

/* Handle BREAKs */
sci_handle_breaks(port);
+
+ /* drop invalid character received before break was detected */
+ serial_port_in(port, SCxRDR);
+
sci_clear_SCxSR(port, SCxSR_BREAK_CLEAR(port));

return IRQ_HANDLED;
@@ -1829,7 +1833,8 @@ static irqreturn_t sci_mpxed_interrupt(int irq, void *ptr)
ret = sci_er_interrupt(irq, ptr);

/* Break Interrupt */
- if ((ssr_status & SCxSR_BRK(port)) && err_enabled)
+ if (s->irqs[SCIx_ERI_IRQ] != s->irqs[SCIx_BRI_IRQ] &&
+ (ssr_status & SCxSR_BRK(port)) && err_enabled)
ret = sci_br_interrupt(irq, ptr);

/* Overrun Interrupt */
--
2.30.2