timekeeping: Provide new API to get the current time resolution

This patch series introduces a new function
u32 ktime_get_resolution_ns(void)
which allows to clean up some driver code.

In particular the IIO subsystem has a function to provide timestamps for
events but no means to get their resolution. So currently the dht11 driver
tries to guess the resolution in a rather messy and convoluted way. We
can do much better with the new code.

This API is not designed to be exposed to user space.

This has been tested on i386, sunxi and mxs.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Harald Geyer <harald@ccbib.org>
[jstultz: Tweaked to make it build after upstream changes]
Signed-off-by: John Stultz <john.stultz@linaro.org>

diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h
index 99176af216af449563e3a190b96edc04ea1a1f9e..9af5c1214682e6b42a883754f12c2892ac880368 100644 (file)
--- a/include/linux/timekeeping.h
+++ b/include/linux/timekeeping.h
@@ -163,6 +163,7 @@ extern ktime_t ktime_get(void);
 extern ktime_t ktime_get_with_offset(enum tk_offsets offs);
 extern ktime_t ktime_mono_to_any(ktime_t tmono, enum tk_offsets offs);
 extern ktime_t ktime_get_raw(void);
+extern u32 ktime_get_resolution_ns(void);
 
 /**
  * ktime_get_real - get the real (wall-) time in ktime_t format

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 3365e32dc2086f4afc82d3147be7826e634f0bf8..85d3763963135cbbdc194fea894452b7f74c0c9b 100644 (file)
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -702,6 +702,23 @@ ktime_t ktime_get(void)
 }
 EXPORT_SYMBOL_GPL(ktime_get);
 
+u32 ktime_get_resolution_ns(void)
+{
+       struct timekeeper *tk = &tk_core.timekeeper;
+       unsigned int seq;
+       u32 nsecs;
+
+       WARN_ON(timekeeping_suspended);
+
+       do {
+               seq = read_seqcount_begin(&tk_core.seq);
+               nsecs = tk->tkr_mono.mult >> tk->tkr_mono.shift;
+       } while (read_seqcount_retry(&tk_core.seq, seq));
+
+       return nsecs;
+}
+EXPORT_SYMBOL_GPL(ktime_get_resolution_ns);
+
 static ktime_t *offsets[TK_OFFS_MAX] = {
        [TK_OFFS_REAL]  = &tk_core.timekeeper.offs_real,
        [TK_OFFS_BOOT]  = &tk_core.timekeeper.offs_boot,