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authorCarlo Caione <carlo.caione@gmail.com>2011-06-21 20:56:53 +0200
committerSascha Hauer <s.hauer@pengutronix.de>2011-06-22 00:17:56 +0200
commit701edd4d986841359a135e53d93e7472f5859435 (patch)
tree61f6179c174911bbe555d0062b47ce12eae3beb5 /common/clock.c
parentf568880f8f560938650896284950338592d0f8fa (diff)
downloadbarebox-701edd4d986841359a135e53d93e7472f5859435.tar.gz
shift and clocksource
Added clocks_calc_mult_shift() Signed-off-by: Carlo Caione <carlo.caione@gmail.com> Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Diffstat (limited to 'common/clock.c')
-rw-r--r--common/clock.c55
1 files changed, 55 insertions, 0 deletions
diff --git a/common/clock.c b/common/clock.c
index 15df0ab..79c06c8 100644
--- a/common/clock.c
+++ b/common/clock.c
@@ -57,6 +57,61 @@ uint64_t get_time_ns(void)
EXPORT_SYMBOL(get_time_ns);
/**
+ * clocks_calc_mult_shift - calculate mult/shift factors for scaled math of clocks
+ * @mult: pointer to mult variable
+ * @shift: pointer to shift variable
+ * @from: frequency to convert from
+ * @to: frequency to convert to
+ * @maxsec: guaranteed runtime conversion range in seconds
+ *
+ * The function evaluates the shift/mult pair for the scaled math
+ * operations of clocksources and clockevents.
+ *
+ * @to and @from are frequency values in HZ. For clock sources @to is
+ * NSEC_PER_SEC == 1GHz and @from is the counter frequency. For clock
+ * event @to is the counter frequency and @from is NSEC_PER_SEC.
+ *
+ * The @maxsec conversion range argument controls the time frame in
+ * seconds which must be covered by the runtime conversion with the
+ * calculated mult and shift factors. This guarantees that no 64bit
+ * overflow happens when the input value of the conversion is
+ * multiplied with the calculated mult factor. Larger ranges may
+ * reduce the conversion accuracy by chosing smaller mult and shift
+ * factors.
+ */
+
+void clocks_calc_mult_shift(uint32_t *mult, uint32_t *shift, uint32_t from, uint32_t to, uint32_t maxsec)
+{
+ uint64_t tmp;
+ uint32_t sft, sftacc = 32;
+
+ /*
+ * Calculate the shift factor which is limiting the conversion
+ * range:
+ */
+ tmp = ((uint64_t)maxsec * from) >> 32;
+ while (tmp) {
+ tmp >>=1;
+ sftacc--;
+ }
+
+ /*
+ * Find the conversion shift/mult pair which has the best
+ * accuracy and fits the maxsec conversion range:
+ */
+ for (sft = 32; sft > 0; sft--) {
+ tmp = (uint64_t) to << sft;
+ tmp += from / 2;
+ do_div(tmp, from);
+ if ((tmp >> sftacc) == 0)
+ break;
+ }
+ *mult = tmp;
+ *shift = sft;
+}
+
+
+/**
* clocksource_hz2mult - calculates mult from hz and shift
* @hz: Clocksource frequency in Hz
* @shift_constant: Clocksource shift factor