From 33dfda973ac3e937afa23c948e62dd90ec3abd94 Mon Sep 17 00:00:00 2001
From: hpa <hpa>
Date: Mon, 29 Aug 2005 20:24:29 +0000
Subject: [PATCH] Enable the 16550A FIFO when doing serial console

---
 NEWS            |  2 ++
 parseconfig.inc | 23 ++++++++++++++++++++++-
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/NEWS b/NEWS
index e23fbd9..ccec82a 100644
--- a/NEWS
+++ b/NEWS
@@ -12,6 +12,8 @@ Changes in 3.11:
 	  problems on some network cards.
 	* MEMDISK: Try work around a bug on some BIOSes when no
 	  physical floppy disk is present in the system.
+	* Enable the 16550A FIFOs, if present, when doing serial
+	  console.
 
 Changes in 3.10:
 	* gcc 4.0.1 compilation fixes.
diff --git a/parseconfig.inc b/parseconfig.inc
index 30fd544..09712b9 100644
--- a/parseconfig.inc
+++ b/parseconfig.inc
@@ -197,18 +197,26 @@ pc_serial:	call getint
 		mov di,[di+serial_base]		; Get the I/O port from the BIOS
 .port_is_io:
 		mov [SerialPort],di
+
+		;
+		; Begin code to actually set up the serial port
+		;
 		lea dx,[di+3]			; DX -> LCR
 		mov al,83h			; Enable DLAB
 		call slow_out
+
 		pop ax				; Divisor
 		mov dx,di			; DX -> LS
 		call slow_out
+
 		inc dx				; DX -> MS
 		mov al,ah
 		call slow_out
+
 		mov al,03h			; Disable DLAB
 		add dx,byte 2			; DX -> LCR
 		call slow_out
+
 		in al,dx			; Read back LCR (detect missing hw)
 		cmp al,03h			; If nothing here we'll read 00 or FF
 		jne .serial_port_bad		; Assume serial port busted
@@ -216,7 +224,20 @@ pc_serial:	call getint
 		xor al,al			; IRQ disable
 		call slow_out
 
-		add dx,byte 3			; DX -> MCR
+		inc dx
+		inc dx				; DX -> FCR
+		mov al,01h
+		call slow_out			; Enable FIFOs if present
+		dec dx				; DX -> IIR
+		in al,dx
+		inc dx				; DX -> FCR
+		cmp al,0C0h			; FIFOs enabled and usable?
+		jae .fifo_ok
+		xor ax,ax			; Disable FIFO if unusable
+		call slow_out
+.fifo_ok:
+
+		inc dx				; DX -> MCR
 		in al,dx
 		or al,[FlowOutput]		; Assert bits
 		call slow_out
-- 
2.7.4