[PATCH v2] arm: mach-k3: am625_init: Add Erratum WA for RTC startup

[Bryan Brattlof]

From: Nishanth Menon <nm at ti.com>

In the first silicon revision of the am62x family of SoCs, the hardware
wakeup event cannot be used if software is unable to unlock the RTC
device within one second after boot. To work around this limitation
unlock RTC as soon as possible in the boot flow to maximize our chance
of linux being able to use this device.

Add the erratum i2327 workaround to initialize the RTC.

Signed-off-by: Nishanth Menon <nm at ti.com>
[bb at ti.com: rebased from 2021.01 and expanded commit and code messages]
Signed-off-by: Bryan Brattlof <bb at ti.com>
---
 arch/arm/mach-k3/am625_init.c | 46 +++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/arch/arm/mach-k3/am625_init.c b/arch/arm/mach-k3/am625_init.c
index 026c4f9c02d71..787fe9229552f 100644
--- a/arch/arm/mach-k3/am625_init.c
+++ b/arch/arm/mach-k3/am625_init.c
@@ -15,6 +15,15 @@
 #include <dm/uclass-internal.h>
 #include <dm/pinctrl.h>
 
+#define RTC_BASE_ADDRESS		0x2b1f0000
+#define REG_K3RTC_S_CNT_LSW		(RTC_BASE_ADDRESS + 0x18)
+#define REG_K3RTC_KICK0			(RTC_BASE_ADDRESS + 0x70)
+#define REG_K3RTC_KICK1			(RTC_BASE_ADDRESS + 0x74)
+
+/* Magic values for lock/unlock */
+#define K3RTC_KICK0_UNLOCK_VALUE	0x83e70b13
+#define K3RTC_KICK1_UNLOCK_VALUE	0x95a4f1e0
+
 /*
  * This uninitialized global variable would normal end up in the .bss section,
  * but the .bss is cleared between writing and reading this variable, so move
@@ -71,6 +80,42 @@ static __maybe_unused void enable_mcu_esm_reset(void)
 	writel(stat, CTRLMMR_MCU_RST_CTRL);
 }
 
+#if defined(CONFIG_CPU_V7R)
+
+/*
+ * RTC Erratum i2327 Workaround for Silicon Revision 1
+ *
+ * Due to a bug in initial synchronization out of cold power on,
+ * IRQ status can get locked infinitely if we do not unlock RTC
+ *
+ * This workaround *must* be applied within 1 second of power on,
+ * So, this is closest point to be able to guarantee the max
+ * timing.
+ *
+ * https://www.ti.com/lit/er/sprz487c/sprz487c.pdf
+ */
+void rtc_erratumi2327_init(void)
+{
+	u32 counter;
+
+	/*
+	 * If counter has gone past 1, nothing we can do, leave
+	 * system locked! This is the only way we know if RTC
+	 * can be used for all practical purposes.
+	 */
+	counter = readl(REG_K3RTC_S_CNT_LSW);
+	if (counter > 1)
+		return;
+	/*
+	 * Need to set this up at the very start
+	 * MUST BE DONE under 1 second of boot.
+	 */
+	writel(K3RTC_KICK0_UNLOCK_VALUE, REG_K3RTC_KICK0);
+	writel(K3RTC_KICK1_UNLOCK_VALUE, REG_K3RTC_KICK1);
+	return;
+}
+#endif
+
 void board_init_f(ulong dummy)
 {
 	struct udevice *dev;
@@ -78,6 +123,7 @@ void board_init_f(ulong dummy)
 
 #if defined(CONFIG_CPU_V7R)
 	setup_k3_mpu_regions();
+	rtc_erratumi2327_init();
 #endif
 
 	/*

base-commit: 6e1852ca2c418e2536ead4b51c4d84a59926b3f1
-- 
2.40.1