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>

1 files changed, 17 insertions, 0 deletions

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 3365e32dc208..85d376396313 100644
--- 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,