From 8ce912ef039c4e5a3d6d7b49af03e6392bfa1858 Mon Sep 17 00:00:00 2001
From: Stefan Lankes <slankes@eonerc.rwth-aachen.de>
Date: Fri, 2 Jun 2017 20:13:09 +0200
Subject: [PATCH] before writing to UART, check if the fifo is free

---
 arch/x86/kernel/uart.c | 10 ++++++++++
 arch/x86/loader/uart.c | 10 ++++++++++
 2 files changed, 20 insertions(+)

diff --git a/arch/x86/kernel/uart.c b/arch/x86/kernel/uart.c
index 1962b885d..7631dc88e 100644
--- a/arch/x86/kernel/uart.c
+++ b/arch/x86/kernel/uart.c
@@ -111,8 +111,18 @@ static inline unsigned char read_from_uart(uint32_t off)
 	return c;
 }
 
+static inline int is_transmit_empty(void)
+{
+	if (uartport)
+		return inportb(uartport + UART_LSR) & 0x20;
+
+	return 1;
+}
+
 static inline void write_to_uart(uint32_t off, unsigned char c)
 {
+	while (is_transmit_empty() == 0) { PAUSE; }
+
 	if (uartport)
 		outportb(uartport + off, c);
 }
diff --git a/arch/x86/loader/uart.c b/arch/x86/loader/uart.c
index 3130260ba..8141a61a6 100644
--- a/arch/x86/loader/uart.c
+++ b/arch/x86/loader/uart.c
@@ -104,8 +104,18 @@ static inline unsigned char read_from_uart(uint32_t off)
 	return c;
 }
 
+static inline int is_transmit_empty(void)
+{
+	if (uartport)
+		return inportb(uartport + UART_LSR) & 0x20;
+
+	return 1;
+}
+
 static void write_to_uart(uint32_t off, unsigned char c)
 {
+	while (is_transmit_empty() == 0) ;
+
 	if (uartport)
 		outportb(uartport + off, c);
 }