sandbox: keep time offset when resetting

The UEFI Self Certification Test (SCT) checks the SetTime() service with
the following steps:

* set date
* reset
* check date matches

To be compliant the sandbox should keep the offset to the host RTC during
resets. The implementation uses the environment variable
UBOOT_SB_TIME_OFFSET to persist the offset.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>

arch/sandbox/cpu/os.c

@@ -32,6 +32,9 @@
 #include <os.h>
 #include <rtc_def.h>
 
+/* Environment variable for time offset */
+#define ENV_TIME_OFFSET "UBOOT_SB_TIME_OFFSET"
+
 /* Operating System Interface */
 
 struct os_mem_hdr {
@@ -798,6 +801,28 @@ int os_spl_to_uboot(const char *fname)
 	return os_jump_to_file(fname);
 }
 
+long os_get_time_offset(void)
+{
+	const char *offset;
+
+	offset = getenv(ENV_TIME_OFFSET);
+	if (offset)
+		return strtol(offset, NULL, 0);
+	return 0;
+}
+
+void os_set_time_offset(long offset)
+{
+	char buf[21];
+	int ret;
+
+	snprintf(buf, sizeof(buf), "%ld", offset);
+	ret = setenv(ENV_TIME_OFFSET, buf, true);
+	if (ret)
+		printf("Could not set environment variable %s\n",
+		       ENV_TIME_OFFSET);
+}
+
 void os_localtime(struct rtc_time *rt)
 {
 	time_t t = time(NULL);

doc/arch/sandbox.rst

@@ -131,6 +131,13 @@ available options. Some of these are described below:
 -i
   Go to interactive mode after executing the commands specified by -c.
 
+Environment Variables
+---------------------
+
+UBOOT_SB_TIME_OFFSET
+    This environment variable stores the offset of the emulated real time clock
+    to the host's real time clock in seconds. The offset defaults to zero.
+
 Memory Emulation
 ----------------
 

drivers/rtc/i2c_rtc_emul.c

@@ -57,6 +57,7 @@ long sandbox_i2c_rtc_set_offset(struct udevice *dev, bool use_system_time,
 	plat->use_system_time = use_system_time;
 	if (offset != -1)
 		plat->offset = offset;
+	os_set_time_offset(plat->offset);
 
 	return old_offset;
 }
@@ -80,7 +81,7 @@ static void reset_time(struct udevice *dev)
 
 	os_localtime(&now);
 	plat->base_time = rtc_mktime(&now);
-	plat->offset = 0;
+	plat->offset = os_get_time_offset();
 	plat->use_system_time = true;
 }
 
@@ -115,6 +116,7 @@ static int sandbox_i2c_rtc_set(struct udevice *dev, const struct rtc_time *time)
 		now = plat->base_time;
 	}
 	plat->offset = rtc_mktime(time) - now;
+	os_set_time_offset(plat->offset);
 
 	return 0;
 }

include/os.h

@@ -424,4 +424,22 @@ int os_setup_signal_handlers(void);
  */
 void os_signal_action(int sig, unsigned long pc);
 
+/**
+ * os_get_time_offset() - get time offset
+ *
+ * Get the time offset from environment variable UBOOT_SB_TIME_OFFSET.
+ *
+ * Return:	offset in seconds
+ */
+long os_get_time_offset(void);
+
+/**
+ * os_set_time_offset() - set time offset
+ *
+ * Save the time offset in environment variable UBOOT_SB_TIME_OFFSET.
+ *
+ * @offset:	offset in seconds
+ */
+void os_set_time_offset(long offset);
+
 #endif