kernel: add support for am335x PMIC-base power-off

AM335X SoCs support power-off via a power management
chip (PMIC). An alarm in the real time clock is used
to trigger the PMIC to cut the power.

To ensure the alarm goes off when the system is in
a safe state, the RTC is frozen when the alarm is
set. At the last moment, the kernel unfreezes the RTC
to let the alarm go off.

This patch adds a mini driver for unfreezing the RTC
as well as code to handle RBT_POWEROFF on Minix/arm.

Change-Id: I7d48e75791e3a81bdd2f7704997193a269409fe8

kernel/arch/earm/Makefile.inc

@@ -52,7 +52,7 @@ CPPFLAGS.findfp.c+= -I ${NETBSDSRCDIR}/lib/libc/include
 # that must live in their own unique namespace.
 #
 .for unpaged_obj in head.o pre_init.o direct_tty_utils.o \
-	pg_utils.o klib.o omap_serial.o utility.o arch_reset.o \
+	pg_utils.o klib.o omap_serial.o omap_rtc.o utility.o arch_reset.o \
 	${MINLIB_OBJS_UNPAGED} ${MINC_OBJS_UNPAGED} ${SYS_OBJS_UNPAGED}
 unpaged_${unpaged_obj}: ${unpaged_obj}
 	${OBJCOPY} --prefix-symbols=__k_unpaged_ ${.OBJDIR}/${unpaged_obj} $@
@@ -63,8 +63,8 @@ ORIG_UNPAGED_OBJS += ${unpaged_obj}
 CLEANFILES+= ${ORIG_UNPAGED_OBJS}
 
 SRCS+=	mpx.S arch_clock.c arch_do_vmctl.c arch_system.c \
-	omap_serial.c omap_timer.c omap_padconf.c omap_intr.c exception.c \
-	klib.S memory.c \
+	omap_serial.c omap_timer.c omap_padconf.c omap_intr.c omap_rtc.c \
+	exception.c klib.S memory.c \
 	protect.c direct_tty_utils.c arch_reset.c \
 	pg_utils.c phys_copy.S phys_memset.S exc.S
 OBJS.kernel+=	${UNPAGED_OBJS}

kernel/arch/earm/arch_reset.c

@@ -8,12 +8,15 @@
 #include <assert.h>
 #include <signal.h>
 #include <machine/vm.h>
+#include <io.h>
 
+#include <minix/reboot.h>
 #include <minix/u64.h>
 
 #include "archconst.h"
 #include "arch_proto.h"
 #include "serial.h"
+#include "omap_rtc.h"
 #include "kernel/proc.h"
 #include "kernel/debug.h"
 #include "direct_utils.h"
@@ -34,9 +37,48 @@ reset(void)
     while (1);
 }
 
+void
+poweroff(void)
+{
+
+/*
+ * The am335x can signal an external power management chip to cut the power
+ * by toggling the PMIC_POWER_EN pin. It might fail if there isn't an
+ * external PMIC or if the PMIC hasn't been configured to respond to toggles.
+ * The only way to pull the pin low is via ALARM2 (see TRM 20.3.3.8).
+ * At this point PM should have already signaled readclock to set the alarm.
+ */
+#ifdef AM335X
+
+	/* Powers down the SoC within 3 seconds */
+	direct_print("PMIC Power-Off in 3 Seconds\n");
+
+	/* rtc was frozen to prevent premature power-off, unfreeze it now */
+	omap3_rtc_run();
+
+	/* wait for the alarm to go off and PMIC to disable power to SoC */
+	while (1);
+
+#endif /* AM335X */
+
+	/* fallback option: hang */
+	direct_print("Unable to power-off this device.");
+	while (1);
+}
+
 __dead void
 arch_shutdown(int how)
 {
+	switch (how) {
+
+	case RBT_POWEROFF:
+		/* Power off if possible, hang otherwise */
+		poweroff();
+		NOT_REACHABLE;
+
+	default:
+		break;
+	}
 	while (1);
 }
 

kernel/arch/earm/arch_system.c

@@ -128,6 +128,9 @@ void arch_init(void)
 
 	/* configure i2c pinmux */
 	omap3_padconf_init();
+
+	/* map memory for rtc */
+	omap3_rtc_init();
 }
 
 /*===========================================================================*

kernel/arch/earm/omap_rtc.c

@@ -0,0 +1,55 @@
+/*
+ * This is a mini driver for the AM335X Real Time Clock. The majority of the
+ * work is done in user space in readclock, but for power-off the clock needs
+ * to be put into run mode at the last possible moment in arch_reset.c. This
+ * driver just implements mapping the memory and re-starting the clock.
+ */
+
+#include <assert.h>
+#include <sys/types.h>
+#include <machine/cpu.h>
+#include <minix/type.h>
+#include <io.h>
+
+#include "kernel/kernel.h"
+#include "kernel/proc.h"
+#include "kernel/vm.h"
+#include "kernel/proto.h"
+#include "arch_proto.h"
+#include "omap_rtc.h"
+
+#define RTC_SS_BASE 0x44e3e000
+#define RTC_SS_SIZE 0x1000
+#define RTC_CTRL_REG 0x40
+#define RTC_CTRL_RTC_STOP_BIT 0
+
+struct omap_rtc
+{
+	vir_bytes base;
+	vir_bytes size;
+};
+
+static struct omap_rtc omap_rtc = {
+	.base = RTC_SS_BASE,
+	.size = RTC_SS_SIZE
+};
+
+static kern_phys_map rtc_phys_map;
+
+void
+omap3_rtc_init(void)
+{
+#ifdef AM335X
+	kern_phys_map_ptr(omap_rtc.base, omap_rtc.size, &rtc_phys_map,
+	    &omap_rtc.base);
+#endif /* AM335X */
+}
+
+void
+omap3_rtc_run(void)
+{
+#ifdef AM335X
+	/* Setting the stop bit starts the RTC running */
+	mmio_set((omap_rtc.base + RTC_CTRL_REG), (1 << RTC_CTRL_RTC_STOP_BIT));
+#endif /* AM335X */
+}

kernel/arch/earm/omap_rtc.h

@@ -0,0 +1,7 @@
+#ifndef __OMAP_RTC_H
+#define __OMAP_RTC_H
+
+void omap3_rtc_init(void);
+void omap3_rtc_run(void);
+
+#endif /* __OMAP_RTC_H */