soc/cavium: Clean uart code

* Only init UART_FOR_CONSOLE
* Allow UART init with zero baudrate.
* Init UART0..3 on Cavium's cn8100_sff_evb to fix kernel panic.

Tested on CN8100_SFF_EVB.

Change-Id: I1043b30318ec6210e2dd6b7ac313a41171d37f55
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-on: https://review.coreboot.org/25448
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: David Hendricks <david.hendricks@gmail.com>

src/mainboard/cavium/cn8100_sff_evb/bootblock.c

@@ -21,10 +21,8 @@
 void bootblock_mainboard_early_init(void)
 {
 	if (IS_ENABLED(CONFIG_BOOTBLOCK_CONSOLE)) {
-		if (!uart_is_enabled(0))
+		if (!uart_is_enabled(CONFIG_UART_FOR_CONSOLE))
-			uart_setup(0, CONFIG_TTYS0_BAUD);
+			uart_setup(CONFIG_UART_FOR_CONSOLE, CONFIG_TTYS0_BAUD);
-		if (!uart_is_enabled(1))
-			uart_setup(0, CONFIG_TTYS0_BAUD);
 	}
 }
 

src/mainboard/cavium/cn8100_sff_evb/mainboard.c

@@ -22,12 +22,19 @@
 #include <soc/twsi.h>
 #include <soc/gpio.h>
 #include <delay.h>
+#include <soc/uart.h>
 
 extern const struct bdk_devicetree_key_value devtree[];
 
 static void mainboard_init(struct device *dev)
 {
-	/* FIXME: stub */
+	size_t i;
+
+	/* Init UARTs */
+	for (i = 0; i < 4; i++) {
+		if (!uart_is_enabled(i))
+			uart_setup(i, 0);
+	}
 }
 
 static void mainboard_enable(struct device *dev)

src/soc/cavium/cn81xx/uart.c

@@ -232,6 +232,14 @@ int uart_setup(const size_t bus, int baudrate)
 	ctl.s.csclk_en = 1;
 	write64(&uart->uctl_ctl, ctl.u);
 
+	/**
+	 * Exit here if the UART is not going to be used in coreboot.
+	 * The previous initialization steps are sufficient to make the Linux
+	 * kernel not panic.
+	 */
+	if (!baudrate)
+		return 0;
+
 	/**
 	 * 7. Initialize the integer and fractional baud rate divider registers
 	 * UARTIBRD and UARTFBRD as follows: