backports: make backports-4.18 compatible with kernel < 3.19

backports-4.18.c uses ktime_divns() function.
As ktime_divns() is not exported in kernel < 3.19, this symbol
will not be resolved on compat.ko loading.
This commit fixes the linking issue [1].

[1]
-------------------------------
WARNING: "ktime_divns" [compat/compat.ko] undefined!
-------------------------------

Signed-off-by: Oleksandr Suvorov <oleksandr.suvorov@toradex.com>

1 files changed, 36 insertions, 0 deletions

diff --git a/backport/compat/backport-4.18.c b/backport/compat/backport-4.18.c
index c47fabe5..40551c76 100644
--- a/backport/compat/backport-4.18.c
+++ b/backport/compat/backport-4.18.c
@@ -1,11 +1,47 @@
 /*
  * Copyright (C) 2018 Intel Corporation
+ * Copyright (c) 2020 Toradex
  */
 
 #include <linux/hrtimer.h>
 
+/*
+ * Before the commit 8b618628b2b the ktime_divns was non-exported function.
+ * Add the simple implementation of ktime_divns() to use in
+ * ktime_get_boottime_seconds().
+ */
+#if LINUX_VERSION_IS_LESS(3,19,0)
+
+#include <linux/ktime.h>
+
+#if BITS_PER_LONG < 64
+/*
+ * Divide a ktime value by a nanosecond value
+ */
+u64 ktime_divns(const ktime_t kt, s64 div)
+{
+	int sft = 0;
+	s64 dclc;
+	u64 tmp;
+
+	dclc = ktime_to_ns(kt);
+	tmp = dclc < 0 ? -dclc : dclc;
+
+	/* Make sure the divisor is less than 2^32: */
+	while (div >> 32) {
+		sft++;
+		div >>= 1;
+	}
+	tmp >>= sft;
+	do_div(tmp, (unsigned long) div);
+	return dclc < 0 ? -tmp : tmp;
+}
+#endif /* BITS_PER_LONG >= 64 */
+#endif /* < 3.19 */
+
 time64_t ktime_get_boottime_seconds(void)
 {
 	return ktime_divns(ktime_get_boottime(), NSEC_PER_SEC);
 }
 EXPORT_SYMBOL_GPL(ktime_get_boottime_seconds);
+