serial: sh-sci: fix break handling for sysrq

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@fpond.eu>
Link: https://lore.kernel.org/r/20210816162201.28801-1-uli+renesas@fpond.eu
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
index 07eb56294371bb6c4f7ce511b1c4f64d44e530b7..89ee43061d3ae5aa77565c44394920fb4a591f0a 100644 (file)
--- a/drivers/tty/serial/sh-sci.c
+++ b/drivers/tty/serial/sh-sci.c
@@ -1758,6 +1758,10 @@ 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;
@@ -1837,7 +1841,8 @@ 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 */