arm, am33x: make RTC32K OSC enable configurable

As
http://www.denx.de/wiki/view/U-Boot/DesignPrinciples#2_Keep_it_Fast
states:
"Initialize devices only when they are needed within U-Boot"

enable the RTC32K OSC only, if CONFIG_SPL_AM33XX_ENABLE_RTC32K_OSC is
enabled. Enable this in ti_am335x_common.h, so all boards in mainline
should work as before.

Signed-off-by: Heiko Schocher <hs@denx.de>
Cc: Tom Rini <trini@ti.com>

README

@@ -4319,6 +4319,9 @@ Low Level (hardware related) configuration options:
 
 		NOTE : currently only supported on AM335x platforms.
 
+- CONFIG_SPL_AM33XX_ENABLE_RTC32K_OSC:
+		Enables the RTC32K OSC on AM33xx based plattforms
+
 Freescale QE/FMAN Firmware Support:
 -----------------------------------
 

arch/arm/cpu/armv7/am33xx/board.c

@@ -149,6 +149,7 @@ __weak void am33xx_spl_board_init(void)
 	do_setup_dpll(&dpll_mpu_regs, &dpll_mpu_opp100);
 }
 
+#if defined(CONFIG_SPL_AM33XX_ENABLE_RTC32K_OSC)
 static void rtc32k_enable(void)
 {
 	struct davinci_rtc *rtc = (struct davinci_rtc *)RTC_BASE;
@@ -164,6 +165,7 @@ static void rtc32k_enable(void)
 	/* Enable the RTC 32K OSC by setting bits 3 and 6. */
 	writel((1 << 3) | (1 << 6), &rtc->osc);
 }
+#endif
 
 static void uart_soft_reset(void)
 {
@@ -232,8 +234,10 @@ void s_init(void)
 #if defined(CONFIG_SPL_BUILD) || defined(CONFIG_NOR_BOOT)
 	prcm_init();
 	set_mux_conf_regs();
+#if defined(CONFIG_SPL_AM33XX_ENABLE_RTC32K_OSC)
 	/* Enable RTC32K clock */
 	rtc32k_enable();
+#endif
 	sdram_init();
 #endif
 }

include/configs/ti_am335x_common.h

@@ -18,6 +18,7 @@
 #define CONFIG_SYS_CACHELINE_SIZE       64
 #define CONFIG_MAX_RAM_BANK_SIZE	(1024 << 20)	/* 1GB */
 #define CONFIG_SYS_TIMERBASE		0x48040000	/* Use Timer2 */
+#define CONFIG_SPL_AM33XX_ENABLE_RTC32K_OSC
 
 #include <asm/arch/omap.h>