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>

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

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.
 

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);
 }