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 <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/sh-sci.c

···
 
 	/* 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;
···
 		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 */