[PATCH] serial: Detect XR16C2852 UARTs correctly

[Matthias Fuchs <mfuchs@ma-fu.de>]

Without this patch Exar XR16C2852 UARTs are detected
as Motorola 8xxx DUARTs (16550A compatible).

By checking the fifo size it is possible to
continue probing for the correct UART type.

Signed-off-by: Matthias Fuchs <mfuchs@ma-fu.de>
---
 drivers/serial/8250.c |   22 +++++++++++++++++++---
 1 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c
index 303272a..ec27086 100644
--- a/drivers/serial/8250.c
+++ b/drivers/serial/8250.c
@@ -782,7 +782,7 @@ static void autoconfig_has_efr(struct uart_8250_port *up)
 	 * reading back DLL and DLM.  The chip type depends on the DLM
 	 * value read back:
 	 *  0x10 - XR16C850 and the DLL contains the chip revision.
-	 *  0x12 - XR16C2850.
+	 *  0x12 - XR16C2850 + XR16C2852.
 	 *  0x14 - XR16C854.
 	 */
 	id1 = autoconfig_read_divisor_id(up);
@@ -869,11 +869,27 @@ static void autoconfig_16550a(struct uart_8250_port *up)
 			DEBUG_AUTOCONF("EFRv1 ");
 			up->port.type = PORT_16650;
 			up->capabilities |= UART_CAP_EFR | UART_CAP_SLEEP;
+			serial_outp(up, UART_EFR, 0);
+			return;
 		} else {
-			DEBUG_AUTOCONF("Motorola 8xxx DUART ");
+			int sf = size_fifo(up);
+			DEBUG_AUTOCONF("sf=%d ", sf);
+			/*
+			 * This fifo size check is needed to detect
+			 * Exar XR16C2852 UARTs later on.
+			 * These devices have an AFR register at
+			 * UART_EFR's address with LCR_DLAB set.
+			 * Because of thier 128 byte fifo we can
+			 * skip this point of return and let
+			 * autoconfig_has_efr() detect them later.
+			 */
+			if (sf != 128) {
+				DEBUG_AUTOCONF("Motorola 8xxx DUART ");
+				serial_outp(up, UART_EFR, 0);
+				return;
+			}
 		}
 		serial_outp(up, UART_EFR, 0);
-		return;
 	}
 
 	/*
-- 
1.5.6.3