[PATCH 2/7] serial: sh-sci: consider DR (data ready) bit adequately

[Ulrich Hecht <ulrich.hecht+renesas@xxxxxxxxx>]

To allow operation with a higher RX FIFO interrupt threshold in PIO
mode, it is necessary to consider the DR bit ("FIFO not full, but no
data received for 1.5 frames") as an indicator that data can be read.
Otherwise the driver will let data rot in the FIFO until the threshold
is reached.

Signed-off-by: Ulrich Hecht <ulrich.hecht+renesas@xxxxxxxxx>
---
 drivers/tty/serial/sh-sci.c | 9 +++++----
 drivers/tty/serial/sh-sci.h | 1 +
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
index 385afbe..de25db8 100644
--- a/drivers/tty/serial/sh-sci.c
+++ b/drivers/tty/serial/sh-sci.c
@@ -677,7 +677,7 @@ static int sci_poll_get_char(struct uart_port *port)
 		break;
 	} while (1);
 
-	if (!(status & SCxSR_RDxF(port)))
+	if (!(status & (SCxSR_RDxF(port) | SCxSR_DR(port))))
 		return NO_POLL_CHAR;
 
 	c = serial_port_in(port, SCxRDR);
@@ -773,7 +773,8 @@ static int sci_rxfill(struct uart_port *port)
 	if (reg->size)
 		return serial_port_in(port, SCFDR) & ((port->fifosize << 1) - 1);
 
-	return (serial_port_in(port, SCxSR) & SCxSR_RDxF(port)) != 0;
+	return (serial_port_in(port, SCxSR) &
+		(SCxSR_RDxF(port) | SCxSR_DR(port))) != 0;
 }
 
 /*
@@ -864,7 +865,7 @@ static void sci_receive_chars(struct uart_port *port)
 	unsigned char flag;
 
 	status = serial_port_in(port, SCxSR);
-	if (!(status & SCxSR_RDxF(port)))
+	if (!(status & (SCxSR_RDxF(port) | SCxSR_DR(port))))
 		return;
 
 	while (1) {
@@ -1672,7 +1673,7 @@ static irqreturn_t sci_mpxed_interrupt(int irq, void *ptr)
 	 * Rx Interrupt: if we're using DMA, the DMA controller clears RDF /
 	 * DR flags
 	 */
-	if (((ssr_status & SCxSR_RDxF(port)) || s->chan_rx) &&
+	if (((ssr_status & (SCxSR_RDxF(port) | SCxSR_DR(port))) || s->chan_rx) &&
 	    (scr_status & SCSCR_RIE))
 		ret = sci_rx_interrupt(irq, ptr);
 
diff --git a/drivers/tty/serial/sh-sci.h b/drivers/tty/serial/sh-sci.h
index f51f919..44997a5 100644
--- a/drivers/tty/serial/sh-sci.h
+++ b/drivers/tty/serial/sh-sci.h
@@ -156,6 +156,7 @@ enum {
 #define SCxSR_FER(port)		(((port)->type == PORT_SCI) ? SCI_FER    : SCIF_FER)
 #define SCxSR_PER(port)		(((port)->type == PORT_SCI) ? SCI_PER    : SCIF_PER)
 #define SCxSR_BRK(port)		(((port)->type == PORT_SCI) ? 0x00       : SCIF_BRK)
+#define SCxSR_DR(port)		(((port)->type == PORT_SCI) ? 0x00       : SCIF_DR)
 
 #define SCxSR_ERRORS(port)	(to_sci_port(port)->error_mask)
 
-- 
2.7.4