clocksource: Simplify the clocks_calc_max_nsecs() logic

[deliverable/linux.git] / kernel / time / clocksource.c

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index 4892352f0e4989c561c5d16ba3b27c063082a8f6..2148f413256caa24bfb28babc1b09b75f99bb10e 100644 (file)
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -476,19 +476,10 @@ u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask)
 
        /*
         * Calculate the maximum number of cycles that we can pass to the
-        * cyc2ns function without overflowing a 64-bit signed result. The
-        * maximum number of cycles is equal to ULLONG_MAX/(mult+maxadj)
-        * which is equivalent to the below.
-        * max_cycles < (2^63)/(mult + maxadj)
-        * max_cycles < 2^(log2((2^63)/(mult + maxadj)))
-        * max_cycles < 2^(log2(2^63) - log2(mult + maxadj))
-        * max_cycles < 2^(63 - log2(mult + maxadj))
-        * max_cycles < 1 << (63 - log2(mult + maxadj))
-        * Please note that we add 1 to the result of the log2 to account for
-        * any rounding errors, ensure the above inequality is satisfied and
-        * no overflow will occur.
+        * cyc2ns() function without overflowing a 64-bit result.
         */
-       max_cycles = 1ULL << (63 - (ilog2(mult + maxadj) + 1));
+       max_cycles = ULLONG_MAX;
+       do_div(max_cycles, mult+maxadj);
 
        /*
         * The actual maximum number of cycles we can defer the clocksource is