am335x: Enable RTC 32K OSC clock

In order to support low power state, you must source kernel system
timers to persistent clock, available across suspend/resume.  In case of
AM335x device, the only source we have is, RTC32K, available in
wakeup/always-on domain.  Having said that, during validation it has
been observed that, RTC clock need couple of seconds delay to stabilize
the RTC OSC clock; and such a huge delay is not acceptable in kernel
especially during early init and also it will impact quick/fast boot
use-cases.

So, RTC32k OSC enable dependency has been shifted to
SPL/first-bootloader.

Signed-off-by: Vaibhav Hiremath <hvaibhav@ti.com>
Signed-off-by: Tom Rini <trini@ti.com>

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

@@ -116,11 +116,27 @@ static int read_eeprom(void)
 	return 0;
 }
 
-/* UART Defines */
 #ifdef CONFIG_SPL_BUILD
+/* UART Defines */
 #define UART_RESET		(0x1 << 1)
 #define UART_CLK_RUNNING_MASK	0x1
 #define UART_SMART_IDLE_EN	(0x1 << 0x3)
+
+static void rtc32k_enable(void)
+{
+	struct rtc_regs *rtc = (struct rtc_regs *)AM335X_RTC_BASE;
+
+	/*
+	 * Unlock the RTC's registers.  For more details please see the
+	 * RTC_SS section of the TRM.  In order to unlock we need to
+	 * write these specific values (keys) in this order.
+	 */
+	writel(0x83e70b13, &rtc->kick0r);
+	writel(0x95a4f1e0, &rtc->kick1r);
+
+	/* Enable the RTC 32K OSC by setting bits 3 and 6. */
+	writel((1 << 3) | (1 << 6), &rtc->osc);
+}
 #endif
 
 /*
@@ -154,6 +170,9 @@ void s_init(void)
 	/* Setup the PLLs and the clocks for the peripherals */
 	pll_init();
 
+	/* Enable RTC32K clock */
+	rtc32k_enable();
+
 	/* UART softreset */
 	u32 regVal;
 

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

@@ -44,6 +44,7 @@
 const struct cm_perpll *cmper = (struct cm_perpll *)CM_PER;
 const struct cm_wkuppll *cmwkup = (struct cm_wkuppll *)CM_WKUP;
 const struct cm_dpll *cmdpll = (struct cm_dpll *)CM_DPLL;
+const struct cm_rtc *cmrtc = (struct cm_rtc *)CM_RTC;
 
 static void enable_interface_clocks(void)
 {
@@ -153,6 +154,11 @@ static void enable_per_clocks(void)
 	writel(PRCM_MOD_EN, &cmper->spi0clkctrl);
 	while (readl(&cmper->spi0clkctrl) != PRCM_MOD_EN)
 		;
+
+	/* RTC */
+	writel(PRCM_MOD_EN, &cmrtc->rtcclkctrl);
+	while (readl(&cmrtc->rtcclkctrl) != PRCM_MOD_EN)
+		;
 }
 
 static void mpu_pll_config(void)

arch/arm/include/asm/arch-am33xx/cpu.h

@@ -169,6 +169,12 @@ struct cm_dpll {
 	unsigned int clktimer2clk;	/* offset 0x08 */
 };
 
+/* Control Module RTC registers */
+struct cm_rtc {
+	unsigned int rtcclkctrl;	/* offset 0x0 */
+	unsigned int clkstctrl;		/* offset 0x4 */
+};
+
 /* Watchdog timer registers */
 struct wd_timer {
 	unsigned int resv1[4];
@@ -218,6 +224,15 @@ struct gptimer {
 	unsigned int tcar2;		/* offset 0x58 */
 };
 
+/* RTC Registers */
+struct rtc_regs {
+	unsigned int res[21];
+	unsigned int osc;		/* offset 0x54 */
+	unsigned int res2[5];
+	unsigned int kick0r;		/* offset 0x6c */
+	unsigned int kick1r;		/* offset 0x70 */
+};
+
 /* UART Registers */
 struct uart_sys {
 	unsigned int resv1[21];

arch/arm/include/asm/arch-am33xx/hardware.h

@@ -61,6 +61,7 @@
 #define CM_WKUP				0x44E00400
 #define CM_DPLL				0x44E00500
 #define CM_DEVICE			0x44E00700
+#define CM_RTC				0x44E00800
 #define CM_CEFUSE			0x44E00A00
 #define PRM_DEVICE			0x44E00F00
 
@@ -83,4 +84,7 @@
 #define AM335X_CPSW_BASE		0x4A100000
 #define AM335X_CPSW_MDIO_BASE		0x4A101000
 
+/* RTC base address */
+#define AM335X_RTC_BASE			0x44E3E000
+
 #endif /* __AM33XX_HARDWARE_H */