There are users which print time and date represented by content of
struct rtc_time in human readable format.

Instead of open coding that each time introduce %ptR[dt][r] specifier.

Cc: Arnd Bergmann <a...@arndb.de>
Cc: Bartlomiej Zolnierkiewicz <b.zolnier...@samsung.com>
Cc: Dmitry Torokhov <dmitry.torok...@gmail.com>
Cc: Geert Uytterhoeven <ge...@linux-m68k.org>
Cc: Guan Xuetao <g...@mprc.pku.edu.cn>
Cc: Ingo Molnar <mi...@kernel.org>
Cc: Jason Wessel <jason.wes...@windriver.com>
Cc: Jonathan Corbet <cor...@lwn.net>
Cc: Jonathan Hunter <jonath...@nvidia.com>
Cc: Krzysztof Kozlowski <k...@kernel.org>
Cc: "Rafael J. Wysocki" <r...@rjwysocki.net>
Cc: Thierry Reding <thierry.red...@gmail.com>
Signed-off-by: Andy Shevchenko <andriy.shevche...@linux.intel.com>
---
 Documentation/core-api/printk-formats.rst |  18 ++++
 lib/test_printf.c                         |   6 ++
 lib/vsprintf.c                            | 111 ++++++++++++++++++++++
 3 files changed, 135 insertions(+)

diff --git a/Documentation/core-api/printk-formats.rst 
b/Documentation/core-api/printk-formats.rst
index ff48b55040ef..a7fae4538946 100644
--- a/Documentation/core-api/printk-formats.rst
+++ b/Documentation/core-api/printk-formats.rst
@@ -412,6 +412,24 @@ Examples::
 
 Passed by reference.
 
+Time and date (struct rtc_time)
+-------------------------------
+
+::
+
+       %ptR            YYYY-mm-ddTHH:MM:SS
+       %ptRd           YYYY-mm-dd
+       %ptRt           HH:MM:SS
+       %ptR[dt][r]
+
+For printing date and time as represented by struct rtc_time structure in
+human readable format.
+
+By default year will be incremented by 1900 and month by 1. Use %ptRr (raw)
+to suppress this behaviour.
+
+Passed by reference.
+
 struct clk
 ----------
 
diff --git a/lib/test_printf.c b/lib/test_printf.c
index 53527ea822b5..97b7d14961d6 100644
--- a/lib/test_printf.c
+++ b/lib/test_printf.c
@@ -418,6 +418,11 @@ struct_va_format(void)
 {
 }
 
+static void __init
+struct_rtc_time(void)
+{
+}
+
 static void __init
 struct_clk(void)
 {
@@ -529,6 +534,7 @@ test_pointer(void)
        uuid();
        dentry();
        struct_va_format();
+       struct_rtc_time();
        struct_clk();
        bitmap();
        netdev_features();
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 37a54a6dd594..0a66d0b9c589 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -30,6 +30,7 @@
 #include <linux/ioport.h>
 #include <linux/dcache.h>
 #include <linux/cred.h>
+#include <linux/rtc.h>
 #include <linux/uuid.h>
 #include <linux/of.h>
 #include <net/addrconf.h>
@@ -822,6 +823,20 @@ static const struct printf_spec default_dec_spec = {
        .precision = -1,
 };
 
+static const struct printf_spec default_dec02_spec = {
+       .base = 10,
+       .field_width = 2,
+       .precision = -1,
+       .flags = ZEROPAD,
+};
+
+static const struct printf_spec default_dec04_spec = {
+       .base = 10,
+       .field_width = 4,
+       .precision = -1,
+       .flags = ZEROPAD,
+};
+
 static noinline_for_stack
 char *resource_string(char *buf, char *end, struct resource *res,
                      struct printf_spec spec, const char *fmt)
@@ -1549,6 +1564,98 @@ char *address_val(char *buf, char *end, const void 
*addr, const char *fmt)
        return special_hex_number(buf, end, num, size);
 }
 
+static noinline_for_stack
+char *date_str(char *buf, char *end, const struct rtc_time *tm, bool r)
+{
+       int year = tm->tm_year + (r ? 0 : 1900);
+       int mon = tm->tm_mon + (r ? 0 : 1);
+
+       buf = number(buf, end, year, default_dec04_spec);
+       if (buf < end)
+               *buf = '-';
+       buf++;
+
+       buf = number(buf, end, mon, default_dec02_spec);
+       if (buf < end)
+               *buf = '-';
+       buf++;
+
+       return number(buf, end, tm->tm_mday, default_dec02_spec);
+}
+
+static noinline_for_stack
+char *time_str(char *buf, char *end, const struct rtc_time *tm, bool r)
+{
+       buf = number(buf, end, tm->tm_hour, default_dec02_spec);
+       if (buf < end)
+               *buf = ':';
+       buf++;
+
+       buf = number(buf, end, tm->tm_min, default_dec02_spec);
+       if (buf < end)
+               *buf = ':';
+       buf++;
+
+       return number(buf, end, tm->tm_sec, default_dec02_spec);
+}
+
+static noinline_for_stack
+char *rtc_str(char *buf, char *end, const struct rtc_time *tm, const char *fmt)
+{
+       bool have_t = true, have_d = true;
+       bool raw = false;
+       int count = 2;
+       bool found;
+
+       switch (fmt[count]) {
+       case 'd':
+               have_t = false;
+               count++;
+               break;
+       case 't':
+               have_d = false;
+               count++;
+               break;
+       }
+
+       found = true;
+       do {
+               switch (fmt[count++]) {
+               case 'r':
+                       raw = true;
+                       break;
+               default:
+                       found = false;
+                       break;
+               }
+       } while (found);
+
+       if (have_d)
+               buf = date_str(buf, end, tm, raw);
+       if (have_d && have_t) {
+               /* Respect ISO 8601 */
+               if (buf < end)
+                       *buf = 'T';
+               buf++;
+       }
+       if (have_t)
+               buf = time_str(buf, end, tm, raw);
+
+       return buf;
+}
+
+static noinline_for_stack
+char *timeanddate(char *buf, char *end, void *ptr, struct printf_spec spec,
+                 const char *fmt)
+{
+       switch (fmt[1]) {
+       case 'R':
+               return rtc_str(buf, end, (const struct rtc_time *)ptr, fmt);
+       default:
+               return ptr_to_id(buf, end, ptr, spec);
+       }
+}
+
 static noinline_for_stack
 char *clock(char *buf, char *end, struct clk *clk, struct printf_spec spec,
            const char *fmt)
@@ -1828,6 +1935,8 @@ char *device_node_string(char *buf, char *end, struct 
device_node *dn,
  * - 'd[234]' For a dentry name (optionally 2-4 last components)
  * - 'D[234]' Same as 'd' but for a struct file
  * - 'g' For block_device name (gendisk + partition number)
+ * - 't[R][dt][rv]' For time and date as represented:
+ *      R    struct rtc_time
  * - 'C' For a clock, it prints the name (Common Clock Framework) or address
  *       (legacy clock framework) of the clock
  * - 'Cn' For a clock, it prints the name (Common Clock Framework) or address
@@ -1952,6 +2061,8 @@ char *pointer(const char *fmt, char *buf, char *end, void 
*ptr,
                return address_val(buf, end, ptr, fmt);
        case 'd':
                return dentry_name(buf, end, ptr, spec, fmt);
+       case 't':
+               return timeanddate(buf, end, ptr, spec, fmt);
        case 'C':
                return clock(buf, end, ptr, spec, fmt);
        case 'D':
-- 
2.19.2

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