rtc: NTP: Add CONFIG_RTC_SYSTOHC_DEVICE for NTP synchronization

Currently, CONFIG_RTC_SYSTOHC uses CONFIG_RTC_HCTOSYS_DEVICE which
is originally used by CONFIG_RTC_HCTOSYS, but this rtc device has
some limiations, for example, it must be battery-backed, be able
to work with irq off and through system suspension, etc.

So add CONFIG_RTC_SYSTOHC_DEVICE used exclusively for CONFIG_RTC_SYSTOHC,
it is more lenient compared to CONFIG_RTC_HCTOSYS_DEVICE, and could
be assigned any available RTC in the system.

Default value is CONFIG_RTC_HCTOSYS_DEVICE which is "rtc0" by default.
After this patch, NTP will sync up "rtc0" by default.

Cc: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Xunlei Pang <pang.xunlei@linaro.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

2 files changed, 21 insertions, 10 deletions

diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index c94bb6aded51..efaff368ee94 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -25,17 +25,9 @@ config RTC_HCTOSYS
           the value read from a specified RTC device. This is useful to avoid
           unnecessary fsck runs at boot time, and to network better.
 
-config RTC_SYSTOHC
-        bool "Set the RTC time based on NTP synchronization"
-        default y
-        help
-          If you say yes here, the system time (wall clock) will be stored
-          in the RTC specified by RTC_HCTOSYS_DEVICE approximately every 11
-          minutes if userspace reports synchronized NTP status.
-
 config RTC_HCTOSYS_DEVICE
         string "RTC used to set the system time"
-        depends on RTC_HCTOSYS = y || RTC_SYSTOHC = y
+        depends on RTC_HCTOSYS
         default "rtc0"
         help
           The RTC device that will be used to (re)initialize the system
@@ -56,6 +48,25 @@ config RTC_HCTOSYS_DEVICE
           sleep states. Do not specify an RTC here unless it stays powered
           during all this system's supported sleep states.
 
+config RTC_SYSTOHC
+        bool "Set the RTC time based on NTP synchronization"
+        default y
+        help
+          If you say yes here, the system time (wall clock) will be stored
+          in the RTC specified by RTC_HCTOSYS_DEVICE approximately every 11
+          minutes if userspace reports synchronized NTP status.
+
+config RTC_SYSTOHC_DEVICE
+        string "RTC used to synchronize NTP adjustment"
+        depends on RTC_SYSTOHC
+        default RTC_HCTOSYS_DEVICE if RTC_HCTOSYS
+        default "rtc0"
+        help
+          The RTC device used for NTP synchronization. The main difference
+          between RTC_HCTOSYS_DEVICE and RTC_SYSTOHC_DEVICE is that this
+          one can sleep when setting time, because it runs in the workqueue
+          context.
+
 config RTC_DEBUG
         bool "RTC debug support"
         help
diff --git a/drivers/rtc/systohc.c b/drivers/rtc/systohc.c
index 7728d5e32bf4..b4a68ffcd06b 100644
--- a/drivers/rtc/systohc.c
+++ b/drivers/rtc/systohc.c
@@ -31,7 +31,7 @@ int rtc_set_ntp_time(struct timespec64 now)
         else
                 rtc_time64_to_tm(now.tv_sec + 1, &tm);
 
-        rtc = rtc_class_open(CONFIG_RTC_HCTOSYS_DEVICE);
+        rtc = rtc_class_open(CONFIG_RTC_SYSTOHC_DEVICE);
         if (rtc) {
                 /* rtc_hctosys exclusively uses UTC, so we call set_time here,
                  * not set_mmss. */