rtc: class: support hctosys from modular RTC drivers

Due to distribution constraints it may not be possible to statically
compile the required RTC driver into the kernel.

Expand RTC_HCTOSYS support to cover all RTC devices (statically compiled
or not) by checking at the end of RTC device registration whether the
time should be synced.

Signed-off-by: Steve Muckle <smuckle@google.com>
Link: https://lore.kernel.org/r/20191106194625.116692-1-smuckle@google.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index 6c99156cbe5724bc409ca498af7cd384b06b42bf..417fc6ec9338b9cbcad9a9b64e91913006dc0399 100644 (file)
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -41,9 +41,6 @@ config RTC_HCTOSYS_DEVICE
          device should record time in UTC, since the kernel won't do
          timezone correction.
 
-         The driver for this RTC device must be loaded before late_initcall
-         functions run, so it must usually be statically linked.
-
          This clock should be battery-backed, so that it reads the correct
          time when the system boots from a power-off state. Otherwise, your
          system will need an external clock source (like an NTP server).

diff --git a/drivers/rtc/Makefile b/drivers/rtc/Makefile
index 6c3e93aa36dc40d022931c620ba0706f420bc58a..8642d6f7560d91592944ab83433418ff32a0a0df 100644 (file)
--- a/drivers/rtc/Makefile
+++ b/drivers/rtc/Makefile
@@ -6,7 +6,6 @@
 ccflags-$(CONFIG_RTC_DEBUG)    := -DDEBUG
 
 obj-$(CONFIG_RTC_LIB)          += lib.o
-obj-$(CONFIG_RTC_HCTOSYS)      += hctosys.o
 obj-$(CONFIG_RTC_SYSTOHC)      += systohc.o
 obj-$(CONFIG_RTC_CLASS)                += rtc-core.o
 obj-$(CONFIG_RTC_MC146818_LIB) += rtc-mc146818-lib.o

diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c
index 9458e6d6686aca8aeb6e0722c894114beb6ba652..8793b2b8cf9d9049ed90caf63762e2e0b4ec269b 100644 (file)
--- a/drivers/rtc/class.c
+++ b/drivers/rtc/class.c
@@ -34,6 +34,62 @@ static void rtc_device_release(struct device *dev)
 #ifdef CONFIG_RTC_HCTOSYS_DEVICE
 /* Result of the last RTC to system clock attempt. */
 int rtc_hctosys_ret = -ENODEV;
+
+/* IMPORTANT: the RTC only stores whole seconds. It is arbitrary
+ * whether it stores the most close value or the value with partial
+ * seconds truncated. However, it is important that we use it to store
+ * the truncated value. This is because otherwise it is necessary,
+ * in an rtc sync function, to read both xtime.tv_sec and
+ * xtime.tv_nsec. On some processors (i.e. ARM), an atomic read
+ * of >32bits is not possible. So storing the most close value would
+ * slow down the sync API. So here we have the truncated value and
+ * the best guess is to add 0.5s.
+ */
+
+static int rtc_hctosys(void)
+{
+       int err = -ENODEV;
+       struct rtc_time tm;
+       struct timespec64 tv64 = {
+               .tv_nsec = NSEC_PER_SEC >> 1,
+       };
+       struct rtc_device *rtc = rtc_class_open(CONFIG_RTC_HCTOSYS_DEVICE);
+
+       if (!rtc) {
+               pr_info("unable to open rtc device (%s)\n",
+                       CONFIG_RTC_HCTOSYS_DEVICE);
+               goto err_open;
+       }
+
+       err = rtc_read_time(rtc, &tm);
+       if (err) {
+               dev_err(rtc->dev.parent,
+                       "hctosys: unable to read the hardware clock\n");
+               goto err_read;
+       }
+
+       tv64.tv_sec = rtc_tm_to_time64(&tm);
+
+#if BITS_PER_LONG == 32
+       if (tv64.tv_sec > INT_MAX) {
+               err = -ERANGE;
+               goto err_read;
+       }
+#endif
+
+       err = do_settimeofday64(&tv64);
+
+       dev_info(rtc->dev.parent, "setting system clock to %ptR UTC (%lld)\n",
+                &tm, (long long)tv64.tv_sec);
+
+err_read:
+       rtc_class_close(rtc);
+
+err_open:
+       rtc_hctosys_ret = err;
+
+       return err;
+}
 #endif
 
 #if defined(CONFIG_PM_SLEEP) && defined(CONFIG_RTC_HCTOSYS_DEVICE)
@@ -375,6 +431,11 @@ int __rtc_register_device(struct module *owner, struct rtc_device *rtc)
        dev_info(rtc->dev.parent, "registered as %s\n",
                 dev_name(&rtc->dev));
 
+#ifdef CONFIG_RTC_HCTOSYS_DEVICE
+       if (!strcmp(dev_name(&rtc->dev), CONFIG_RTC_HCTOSYS_DEVICE))
+               rtc_hctosys();
+#endif
+
        return 0;
 }
 EXPORT_SYMBOL_GPL(__rtc_register_device);

diff --git a/drivers/rtc/hctosys.c b/drivers/rtc/hctosys.c
deleted file mode 100644 (file)
index a74d0d8..0000000
--- a/drivers/rtc/hctosys.c
+++ /dev/null
@@ -1,69 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0
-/*
- * RTC subsystem, initialize system time on startup
- *
- * Copyright (C) 2005 Tower Technologies
- * Author: Alessandro Zummo <a.zummo@towertech.it>
- */
-
-#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
-
-#include <linux/rtc.h>
-
-/* IMPORTANT: the RTC only stores whole seconds. It is arbitrary
- * whether it stores the most close value or the value with partial
- * seconds truncated. However, it is important that we use it to store
- * the truncated value. This is because otherwise it is necessary,
- * in an rtc sync function, to read both xtime.tv_sec and
- * xtime.tv_nsec. On some processors (i.e. ARM), an atomic read
- * of >32bits is not possible. So storing the most close value would
- * slow down the sync API. So here we have the truncated value and
- * the best guess is to add 0.5s.
- */
-
-static int __init rtc_hctosys(void)
-{
-       int err = -ENODEV;
-       struct rtc_time tm;
-       struct timespec64 tv64 = {
-               .tv_nsec = NSEC_PER_SEC >> 1,
-       };
-       struct rtc_device *rtc = rtc_class_open(CONFIG_RTC_HCTOSYS_DEVICE);
-
-       if (!rtc) {
-               pr_info("unable to open rtc device (%s)\n",
-                       CONFIG_RTC_HCTOSYS_DEVICE);
-               goto err_open;
-       }
-
-       err = rtc_read_time(rtc, &tm);
-       if (err) {
-               dev_err(rtc->dev.parent,
-                       "hctosys: unable to read the hardware clock\n");
-               goto err_read;
-       }
-
-       tv64.tv_sec = rtc_tm_to_time64(&tm);
-
-#if BITS_PER_LONG == 32
-       if (tv64.tv_sec > INT_MAX) {
-               err = -ERANGE;
-               goto err_read;
-       }
-#endif
-
-       err = do_settimeofday64(&tv64);
-
-       dev_info(rtc->dev.parent, "setting system clock to %ptR UTC (%lld)\n",
-                &tm, (long long)tv64.tv_sec);
-
-err_read:
-       rtc_class_close(rtc);
-
-err_open:
-       rtc_hctosys_ret = err;
-
-       return err;
-}
-
-late_initcall(rtc_hctosys);