[Skiboot] [PATCH] hw/fake-rtc: Add support for emulated rtc clock

[Vaibhav Jain]

This patch adds support for an emulated rtc clock over existing fake rtc
implementation for generic platform (e.g BML). Presently a fake rtc
clock is initialized when reserved region named 'ibm,fake-rtc' is
present in the boot device tree. This mem-region points to the initial
value of bcd coded date-time values. However as this region is in system
memory hence its not updated with time. This results in an error from
hwclock tool which tries to detect a change in system clock and then
complains "Timed out waiting for time change."

The patch overcomes this issue by emulating an rtc clock whose date-time
values are calculated from the difference of current timebase and its
value when the initial epoch was assigned. The initial epoch is set from
the values at "ibm,fake-rtc" memory region.

Acked-by: Michael Neuling <mikey at neuling.org>
Signed-off-by: Vaibhav Jain <vaibhav at linux.vnet.ibm.com>
---
 hw/fake-rtc.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 50 insertions(+), 9 deletions(-)

diff --git a/hw/fake-rtc.c b/hw/fake-rtc.c
index 1b7c473..bf2fc0b 100644
--- a/hw/fake-rtc.c
+++ b/hw/fake-rtc.c
@@ -17,25 +17,53 @@
 #include <skiboot.h>
 #include <opal.h>
 #include <mem_region.h>
+#include <device.h>
+#include <timebase.h>
+#include <time-utils.h>
+#include <lock.h>
 
-static uint32_t *fake_ymd;
-static uint64_t *fake_hmsm;
+/* timebase when tm_offset was assigned */
+static unsigned long tb_synctime;
+
+/*
+ * Absolute time that was last assigned.
+ * Current rtc value is calculated from this.
+*/
+static struct tm tm_offset;
+
+/* protects tm_offset & tb_synctime */
+static struct lock emulation_lock;
 
 static int64_t fake_rtc_write(uint32_t ymd, uint64_t hmsm)
 {
-	*fake_ymd = ymd;
-	*fake_hmsm = hmsm;
+
+	lock(&emulation_lock);
+
+	datetime_to_tm(ymd, hmsm, &tm_offset);
+	tb_synctime = mftb();
+
+	unlock(&emulation_lock);
 
 	return OPAL_SUCCESS;
 }
 
 static int64_t fake_rtc_read(uint32_t *ymd, uint64_t *hmsm)
 {
+
+	time_t sec;
+	struct tm tm_calculated;
+
 	if (!ymd || !hmsm)
 		return OPAL_PARAMETER;
 
-	*ymd = *fake_ymd;
-	*hmsm = *fake_hmsm;
+	/* Compute the emulated clock value */
+	lock(&emulation_lock);
+
+	sec = tb_to_secs(mftb() - tb_synctime) + mktime(&tm_offset);
+	gmtime_r(&sec, &tm_calculated);
+	tm_to_datetime(&tm_calculated, ymd, hmsm);
+
+	unlock(&emulation_lock);
 
 	return OPAL_SUCCESS;
 }
@@ -43,7 +71,9 @@ static int64_t fake_rtc_read(uint32_t *ymd, uint64_t *hmsm)
 void fake_rtc_init(void)
 {
 	struct mem_region *rtc_region = NULL;
-	uint32_t *rtc = NULL;
+	uint32_t *rtc = NULL, *fake_ymd;
+	uint64_t *fake_hmsm;
+	struct dt_node *np;
 
 	/* Read initial values from reserved memory */
 	rtc_region = find_mem_region("ibm,fake-rtc");
@@ -54,14 +84,25 @@ void fake_rtc_init(void)
 		return;
 	}
 
+	init_lock(&emulation_lock);
+
+	/* Fetch the initial rtc values */
 	rtc = (uint32_t *) rtc_region->start;
 
 	fake_ymd = rtc;
 	fake_hmsm = ((uint64_t *) &rtc[1]);
 
-	prlog(PR_TRACE, "Init fake RTC to 0x%x 0x%llx\n",
-	      *fake_ymd, *fake_hmsm);
+	fake_rtc_write(*fake_ymd, *fake_hmsm);
 
+	/* Register opal calls */
 	opal_register(OPAL_RTC_READ, fake_rtc_read, 2);
 	opal_register(OPAL_RTC_WRITE, fake_rtc_write, 2);
+
+	/* add the fake rtc dt node */
+	np = dt_new(opal_node, "rtc");
+	dt_add_property_strings(np, "compatible", "ibm,opal-rtc");
+
+	prlog(PR_TRACE, "Init fake RTC to Date:%d-%d-%d Time:%d-%d-%d\n",
+	      tm_offset.tm_mon, tm_offset.tm_mday, tm_offset.tm_year,
+	      tm_offset.tm_hour, tm_offset.tm_min, tm_offset.tm_sec);
 }
-- 
2.2.1