rtc-proc: permit the /proc/driver/rtc device to use other devices

To get time information via /proc/driver/rtc, only the first device (rtc0)
is used.  If the rtcN (eg.  rtc1 or rtc2) is used for the system clock,
there is no way to get information of rtcN via /proc/driver/rtc.  With
this patch, the time data can be retrieved from the system clock RTC.

If the RTC_HCTOSYS_DEVICE is not defined, then rtc0 is used by default.

Signed-off-by: Milo(Woogyom) Kim <milo.kim@ti.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 31 insertions, 8 deletions

diff --git a/Documentation/rtc.txt b/Documentation/rtc.txt
index 250160469d83..32aa4002de4a 100644
--- a/Documentation/rtc.txt
+++ b/Documentation/rtc.txt
@@ -119,8 +119,9 @@ three different userspace interfaces:
     *   /sys/class/rtc/rtcN ... sysfs attributes support readonly
         access to some RTC attributes.
 
-    *   /proc/driver/rtc ... the first RTC (rtc0) may expose itself
-        using a procfs interface.  More information is (currently) shown
+    *   /proc/driver/rtc ... the system clock RTC may expose itself
+        using a procfs interface. If there is no RTC for the system clock,
+        rtc0 is used by default. More information is (currently) shown
         here than through sysfs.
 
 The RTC Class framework supports a wide variety of RTCs, ranging from those
diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index fabc99a75c65..a4a805c273bb 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -69,13 +69,15 @@ config RTC_INTF_SYSFS
           If unsure, say Y.
 
 config RTC_INTF_PROC
-        boolean "/proc/driver/rtc (procfs for rtc0)"
+        boolean "/proc/driver/rtc (procfs for rtcN)"
         depends on PROC_FS
         default RTC_CLASS
         help
-          Say yes here if you want to use your first RTC through the proc
-          interface, /proc/driver/rtc. Other RTCs will not be available
-          through that API.
+          Say yes here if you want to use your system clock RTC through
+          the proc interface, /proc/driver/rtc.
+          Other RTCs will not be available through that API.
+          If there is no RTC for the system clock, then the first RTC(rtc0)
+          is used by default.
 
           If unsure, say Y.
 
diff --git a/drivers/rtc/rtc-proc.c b/drivers/rtc/rtc-proc.c
index 0a59fda5c09d..e96236ac2e78 100644
--- a/drivers/rtc/rtc-proc.c
+++ b/drivers/rtc/rtc-proc.c
@@ -18,6 +18,26 @@
 
 #include "rtc-core.h"
 
+#define NAME_SIZE       10
+
+#if defined(CONFIG_RTC_HCTOSYS_DEVICE)
+static bool is_rtc_hctosys(struct rtc_device *rtc)
+{
+        int size;
+        char name[NAME_SIZE];
+
+        size = scnprintf(name, NAME_SIZE, "rtc%d", rtc->id);
+        if (size > NAME_SIZE)
+                return false;
+
+        return !strncmp(name, CONFIG_RTC_HCTOSYS_DEVICE, NAME_SIZE);
+}
+#else
+static bool is_rtc_hctosys(struct rtc_device *rtc)
+{
+        return (rtc->id == 0);
+}
+#endif
 
 static int rtc_proc_show(struct seq_file *seq, void *offset)
 {
@@ -117,12 +137,12 @@ static const struct file_operations rtc_proc_fops = {
 
 void rtc_proc_add_device(struct rtc_device *rtc)
 {
-        if (rtc->id == 0)
+        if (is_rtc_hctosys(rtc))
                 proc_create_data("driver/rtc", 0, NULL, &rtc_proc_fops, rtc);
 }
 
 void rtc_proc_del_device(struct rtc_device *rtc)
 {
-        if (rtc->id == 0)
+        if (is_rtc_hctosys(rtc))
                 remove_proc_entry("driver/rtc", NULL);
 }