[PATCH v6 2/8] serial: 8250: share the RX trigger conversion helper

[James Hilliard]

Drivers can supply receive-trigger thresholds through the RX trigger
callbacks without adding a legacy port type to uart_config[]. Extract the
threshold search into serial8250_bytes_to_fcr() so those drivers can use
the same conversion as the generic 8250 implementation.

Keep the implementation in 8250_port.c and export it in the SERIAL_8250
namespace. Include the unsupported-table check and preserve the existing
nearest-lower selection and highest-encoding fallback.

Suggested-by: Andy Shevchenko <andriy.shevchenko at linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko at linux.intel.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen at linux.intel.com>
Signed-off-by: James Hilliard <james.hilliard1 at gmail.com>
---
 drivers/tty/serial/8250/8250.h      |  2 ++
 drivers/tty/serial/8250/8250_port.c | 21 +++++++++++++--------
 2 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
index 21ed9c41b751..1600f2e45d76 100644
--- a/drivers/tty/serial/8250/8250.h
+++ b/drivers/tty/serial/8250/8250.h
@@ -73,6 +73,8 @@ struct serial8250_config {
 	unsigned int	flags;
 };
 
+int serial8250_bytes_to_fcr(const unsigned char *rxtrig_bytes, unsigned char bytes);
+
 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..4a25badad3c5 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -3015,22 +3015,27 @@ static int fcr_get_rxtrig_bytes(struct uart_8250_port *up)
 	return bytes ? bytes : -EOPNOTSUPP;
 }
 
-static int bytes_to_fcr_rxtrig(struct uart_8250_port *up, unsigned char bytes)
+int serial8250_bytes_to_fcr(const unsigned char *rxtrig_bytes, 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)])
+	if (!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])
+	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) << UART_FCR_R_TRIG_SHIFT;
+			return (i - 1) << UART_FCR_R_TRIG_SHIFT;
 	}
 
 	return UART_FCR_R_TRIG_11;
 }
+EXPORT_SYMBOL_NS_GPL(serial8250_bytes_to_fcr, "SERIAL_8250");
+
+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];
+
+	return serial8250_bytes_to_fcr(conf_type->rxtrig_bytes, bytes);
+}
 
 static int do_get_rxtrig(struct tty_port *port)
 {

-- 
2.53.0