[PATCH v4 2/5] serial: 8250: share the RX trigger conversion helper

[James Hilliard]

Extract the receive-trigger threshold search into serial8250_bytes_to_fcr()
so drivers with per-port threshold tables can use the same conversion as
the generic 8250 implementation.

Include the unsupported-table check in the helper and preserve the existing
nearest-lower selection and highest-encoding fallback.

Signed-off-by: James Hilliard <james.hilliard1@xxxxxxxxx>
---
 drivers/tty/serial/8250/8250.h      | 16 ++++++++++++++++
 drivers/tty/serial/8250/8250_port.c | 12 +-----------
 2 files changed, 17 insertions(+), 11 deletions(-)

diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
index 21ed9c41b751..195ed58a2231 100644
--- a/drivers/tty/serial/8250/8250.h
+++ b/drivers/tty/serial/8250/8250.h
@@ -8,6 +8,7 @@
  */
 
 #include <linux/bits.h>
+#include <linux/errno.h>
 #include <linux/serial_8250.h>
 #include <linux/serial_core.h>
 #include <linux/dmaengine.h>
@@ -73,6 +74,21 @@ struct serial8250_config {
 	unsigned int	flags;
 };
 
+static inline int serial8250_bytes_to_fcr(const unsigned char *rxtrig_bytes,
+					  unsigned char bytes)
+{
+	if (!rxtrig_bytes[UART_FCR_R_TRIG_BITS(UART_FCR_R_TRIG_00)])
+		return -EOPNOTSUPP;
+
+	for (unsigned int i = 1; i < UART_FCR_R_TRIG_MAX_STATE; i++) {
+		if (bytes < rxtrig_bytes[i])
+			/* Use the nearest lower value */
+			return (i - 1) << UART_FCR_R_TRIG_SHIFT;
+	}
+
+	return UART_FCR_R_TRIG_11;
+}
+
 enum uart_port_type {
 	/* Internal 8250 only */
 	UART_PORT_AIROHA		= 124,
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 36b2b0a2c05c..c332963dc2ed 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -3018,18 +3018,8 @@ static int fcr_get_rxtrig_bytes(struct uart_8250_port *up)
 static int bytes_to_fcr_rxtrig(struct uart_8250_port *up, unsigned char bytes)
 {
 	const struct serial8250_config *conf_type = &uart_config[up->port.type];
-	int i;
 
-	if (!conf_type->rxtrig_bytes[UART_FCR_R_TRIG_BITS(UART_FCR_R_TRIG_00)])
-		return -EOPNOTSUPP;
-
-	for (i = 1; i < UART_FCR_R_TRIG_MAX_STATE; i++) {
-		if (bytes < conf_type->rxtrig_bytes[i])
-			/* Use the nearest lower value */
-			return (--i) << UART_FCR_R_TRIG_SHIFT;
-	}
-
-	return UART_FCR_R_TRIG_11;
+	return serial8250_bytes_to_fcr(conf_type->rxtrig_bytes, bytes);
 }
 
 static int do_get_rxtrig(struct tty_port *port)

-- 
2.53.0