Blackfin: fix up UART status bit handling

Some Blackfin UARTs are read-to-clear while others are write-to-clear.
This can cause problems when we poll the LSR and then later try and handle
any errors detected.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

cpu/blackfin/serial.c

@@ -35,6 +35,32 @@
 
 #include "serial.h"
 
+#ifdef CONFIG_DEBUG_SERIAL
+uint16_t cached_lsr[256];
+uint16_t cached_rbr[256];
+size_t cache_count;
+
+/* The LSR is read-to-clear on some parts, so we have to make sure status
+ * bits aren't inadvertently lost when doing various tests.
+ */
+static uint16_t uart_lsr_save;
+static uint16_t uart_lsr_read(void)
+{
+	uint16_t lsr = *pUART_LSR;
+	uart_lsr_save |= (lsr & (OE|PE|FE|BI));
+	return lsr | uart_lsr_save;
+}
+/* Just do the clear for everyone since it can't hurt. */
+static void uart_lsr_clear(void)
+{
+	uart_lsr_save = 0;
+	*pUART_LSR |= -1;
+}
+#else
+static inline uint16_t uart_lsr_read(void) { return *pUART_LSR; }
+static inline void uart_lsr_clear(void) { *pUART_LSR = -1; }
+#endif
+
 /* Symbol for our assembly to call. */
 void serial_set_baud(uint32_t baud)
 {
@@ -61,6 +87,12 @@ int serial_init(void)
 {
 	serial_initialize();
 	serial_setbrg();
+	uart_lsr_clear();
+#ifdef CONFIG_DEBUG_SERIAL
+	cache_count = 0;
+	memset(cached_lsr, 0x00, sizeof(cached_lsr));
+	memset(cached_rbr, 0x00, sizeof(cached_rbr));
+#endif
 	return 0;
 }
 
@@ -73,7 +105,7 @@ void serial_putc(const char c)
 	WATCHDOG_RESET();
 
 	/* wait for the hardware fifo to clear up */
-	while (!(*pUART_LSR & THRE))
+	while (!(uart_lsr_read() & THRE))
 		continue;
 
 	/* queue the character for transmission */
@@ -83,38 +115,54 @@ void serial_putc(const char c)
 	WATCHDOG_RESET();
 
 	/* wait for the byte to be shifted over the line */
-	while (!(*pUART_LSR & TEMT))
+	while (!(uart_lsr_read() & TEMT))
 		continue;
 }
 
 int serial_tstc(void)
 {
 	WATCHDOG_RESET();
-	return (*pUART_LSR & DR) ? 1 : 0;
+	return (uart_lsr_read() & DR) ? 1 : 0;
 }
 
 int serial_getc(void)
 {
-	uint16_t uart_lsr_val, uart_rbr_val;
+	uint16_t uart_rbr_val;
 
 	/* wait for data ! */
 	while (!serial_tstc())
 		continue;
 
-	/* clear the status and grab the new byte */
-	uart_lsr_val = *pUART_LSR;
+	/* grab the new byte */
 	uart_rbr_val = *pUART_RBR;
 
+#ifdef CONFIG_DEBUG_SERIAL
+	/* grab & clear the LSR */
+	uint16_t uart_lsr_val = uart_lsr_read();
+
+	cached_lsr[cache_count] = uart_lsr_val;
+	cached_rbr[cache_count] = uart_rbr_val;
+	cache_count = (cache_count + 1) % ARRAY_SIZE(cached_lsr);
+
 	if (uart_lsr_val & (OE|PE|FE|BI)) {
-		/* Some parts are read-to-clear while others are
-		 * write-to-clear.  Just do the write for everyone
-		 * since it cant hurt (other than code size).
-		 */
-		*pUART_LSR = (OE|PE|FE|BI);
+		uint16_t dll, dlh;
+		printf("\n[SERIAL ERROR]\n");
+		ACCESS_LATCH();
+		dll = *pUART_DLL;
+		dlh = *pUART_DLH;
+		ACCESS_PORT_IER();
+		printf("\tDLL=0x%x DLH=0x%x\n", dll, dlh);
+		do {
+			--cache_count;
+			printf("\t%3i: RBR=0x%02x LSR=0x%02x\n", cache_count,
+				cached_rbr[cache_count], cached_lsr[cache_count]);
+		} while (cache_count > 0);
 		return -1;
 	}
+#endif
+	uart_lsr_clear();
 
-	return uart_rbr_val & 0xFF;
+	return uart_rbr_val;
 }
 
 void serial_puts(const char *s)