New patch to review for coreboot: 2a561db Don't loop infinitely long on serial comm failures

[Stefan Reinauer]

Stefan Reinauer ([e-mail]) just uploaded a new patch set to gerrit, which you can find at http://review.coreboot.org/826

-gerrit

commit 2a561dbd95074be053c7c3349a7a62b16889a01d
Author: Stefan Reinauer <[e-mail]>
Date:   Fri Mar 30 16:19:31 2012 -0700

    Don't loop infinitely long on serial comm failures
    
    If serial uart (8250/16x50) takes abnormally long to respond, give
    up on logging to serial console and instead let the system boot.
    
    Also reference bit in LSR register with correct name.
    
    Signed-off-by: Kyösti Mälkki <[e-mail]>
    
    Ported from 9dd3ef165a1bf1bc404056d3e54337de1a15ac90 to
    uart8250mem.c:
    Signed-off-by: Stefan Reinauer <[e-mail]>
    
    Change-Id: Iaca4f57389c887110e6406d45053935891c96838
---
 src/lib/uart8250mem.c |   30 +++++++++++++++++++++---------
 1 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/src/lib/uart8250mem.c b/src/lib/uart8250mem.c
index a38623e..122e475 100644
--- a/src/lib/uart8250mem.c
+++ b/src/lib/uart8250mem.c
@@ -30,21 +30,30 @@
 
 /* Should support 8250, 16450, 16550, 16550A type UARTs */
 
+/* Expected character delay at 1200bps is 9ms for a working UART
+ * and no flow-control. Assume UART as stuck if shift register
+ * or FIFO takes more than 50ms per character to appear empty.
+ *
+ * Estimated that inb() from UART takes 1 microsecond.
+ */
+#define SINGLE_CHAR_TIMEOUT	(50 * 1000)
+#define FIFO_TIMEOUT		(16 * SINGLE_CHAR_TIMEOUT)
+
 static inline int uart8250_mem_can_tx_byte(unsigned base_port)
 {
-	return read8(base_port + UART_LSR) & UART_MSR_DSR;
+	return read8(base_port + UART_LSR) & UART_LSR_THRE;
 }
 
 static inline void uart8250_mem_wait_to_tx_byte(unsigned base_port)
 {
-	while(!uart8250_mem_can_tx_byte(base_port))
-		;
+	unsigned long int i = SINGLE_CHAR_TIMEOUT;
+	while(i-- && !uart8250_mem_can_tx_byte(base_port));
 }
 
 static inline void uart8250_mem_wait_until_sent(unsigned base_port)
 {
-	while(!(read8(base_port + UART_LSR) & UART_LSR_TEMT))
-		;
+	unsigned long int i = FIFO_TIMEOUT;
+	while(i-- && !(read8(base_port + UART_LSR) & UART_LSR_TEMT));
 }
 
 void uart8250_mem_tx_byte(unsigned base_port, unsigned char data)
@@ -65,9 +74,12 @@ int uart8250_mem_can_rx_byte(unsigned base_port)
 
 unsigned char uart8250_mem_rx_byte(unsigned base_port)
 {
-	while(!uart8250_mem_can_rx_byte(base_port))
-		;
-	return read8(base_port + UART_RBR);
+	unsigned long int i = SINGLE_CHAR_TIMEOUT;
+	while(i-- & !uart8250_mem_can_rx_byte(base_port)) ;
+	if (i)
+		return read8(base_port + UART_RBR);
+	else
+		return 0x0;
 }
 
 void uart8250_mem_init(unsigned base_port, unsigned divisor)
@@ -83,7 +95,7 @@ void uart8250_mem_init(unsigned base_port, unsigned divisor)
 	/* DLAB on */
 	write8(base_port + UART_LCR, UART_LCR_DLAB | CONFIG_TTYS0_LCS);
 
-	/* Set Baud Rate Divisor. 12 ==> 115200 Baud */
+	/* Set Baud Rate Divisor. 12 ==> 9600 Baud */
 	write8(base_port + UART_DLL, divisor & 0xFF);
 	write8(base_port + UART_DLM, (divisor >> 8) & 0xFF);