rtc: initialize emulated RTC from environment variable

Up to now the emulated RTC is initialized using the U-Boot build time.

With this patch the environment variable 'rtc_emul_epoch' can be used to
provide a better initial time. The variable is a decimal string with
the number of seconds since 1970-01-01. Here is an example where the RTC
had not been probed yet:

    => setenv rtc_emul_epoch 1610109000
    => date
    Date: 2021-01-08 (Friday)    Time: 12:30:00

If the variable does not exist, the U-Boot build time is used as fallback.

The environment variable may be set when shutting down the operating system
if the U-Boot environment is exposed to the OS (cf. ENV_IS_IN_FAT and
ENV_IS_IN_EXT4).

Suggested-by: Pablo Sebastián Greco <pgreco@centosproject.org>
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index d06d272..cad667a 100644 (file)
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -68,11 +68,14 @@ config RTC_EMULATION
        depends on DM_RTC
        help
          On a board without hardware clock this software real time clock can be
-         used. The build time is used to initialize the RTC. So you will have
-         to adjust the time either manually using the 'date' command  or use
-         the 'sntp' to update the RTC with the time from a network time server.
-         See CONFIG_CMD_SNTP and CONFIG_BOOTP_NTPSERVER. The RTC time is
-         advanced according to CPU ticks.
+         used. The initial time may be provided via the environment variable
+         'rtc_emul_epoch' as a decimal string indicating seconds since
+         1970-01-01. If the environment variable is missing, the build time is
+         used to initialize the RTC. The time can be adjusted manually via the
+         'date' command or the 'sntp' command can be used to update the RTC
+         with the time from a network time server. See CONFIG_CMD_SNTP and
+         CONFIG_BOOTP_NTPSERVER. The RTC time is advanced according to CPU
+         ticks.
 
 config RTC_ISL1208
        bool "Enable ISL1208 driver"

diff --git a/drivers/rtc/emul_rtc.c b/drivers/rtc/emul_rtc.c
index 209b496..7e52210 100644 (file)
--- a/drivers/rtc/emul_rtc.c
+++ b/drivers/rtc/emul_rtc.c
@@ -8,6 +8,7 @@
 #include <common.h>
 #include <div64.h>
 #include <dm.h>
+#include <env.h>
 #include <generated/timestamp_autogenerated.h>
 #include <rtc.h>
 
@@ -60,9 +61,18 @@ static int emul_rtc_set(struct udevice *dev, const struct rtc_time *time)
 int emul_rtc_probe(struct udevice *dev)
 {
        struct emul_rtc *priv = dev_get_priv(dev);
-
-       /* Use the build date as initial time */
-       priv->offset_us = U_BOOT_EPOCH * 1000000ULL - timer_get_us();
+       const char *epoch_str;
+       u64 epoch;
+
+       epoch_str = env_get("rtc_emul_epoch");
+
+       if (epoch_str) {
+               epoch = simple_strtoull(epoch_str, NULL, 10);
+       } else {
+               /* Use the build date as initial time */
+               epoch = U_BOOT_EPOCH;
+       }
+       priv->offset_us = epoch * 1000000ULL - timer_get_us();
        priv->isdst = -1;
 
        return 0;