[PATCH_v2 1/3] clk: clocking-wizard: fix clock difference detection

[Colin Foster]

The diff calculation didn't take into account rollover. As such, a
target clock frequency below the requested rate would not be considered.

Before this change, bogus diffs would be used to determine the closest
possible clock:

8<--------
clk-wizard-test: requesting 133312500 Hz on output 0 (clock NOT enabled)
*** Clock wizard - Matching for rate 133312500 parent rate 99999000
m = 33, d = 1, o = 25, freq = 131998680, diff = 18446744073708237796
m = 34, d = 1, o = 26, freq = 130767923, diff = 18446744073707007039
m = 35, d = 1, o = 26, freq = 134614038, diff = 1301538
m = 36, d = 1, o = 27, freq = 133332000, diff = 19500
8<--------

After this change:

8<--------
clk-wizard-test: requesting 133312500 Hz on output 0 (clock NOT enabled)
*** Clock wizard - Matching for rate 133312500 parent rate 99999000
m = 33, d = 1, o = 25, freq = 131998680, diff = 1313820
m = 35, d = 1, o = 26, freq = 134614038, diff = 1301538
m = 36, d = 1, o = 27, freq = 133332000, diff = 19500
8<--------

Reviewed-by: Shubhrajyoti Datta <shubhrajyoti.datta at amd.com>
Reviewed-by: Brian Masney <bmasney at redhat.com>
Signed-off-by: Colin Foster <colin.foster at in-advantage.com>
---
 drivers/clk/xilinx/clk-xlnx-clock-wizard.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/clk/xilinx/clk-xlnx-clock-wizard.c b/drivers/clk/xilinx/clk-xlnx-clock-wizard.c
index 4a0136349f71a..77c9d025ca8cf 100644
--- a/drivers/clk/xilinx/clk-xlnx-clock-wizard.c
+++ b/drivers/clk/xilinx/clk-xlnx-clock-wizard.c
@@ -406,7 +406,7 @@ static int clk_wzrd_get_divisors(struct clk_hw *hw, unsigned long rate,
 			if (o < omin || o > omax)
 				continue;
 			freq = DIV_ROUND_CLOSEST_ULL(vco_freq, o);
-			diff = freq - rate;
+			diff = abs(freq - rate);
 			if (diff < best_diff) {
 				best_diff = diff;
 				divider->m = m >> 3;
-- 
2.43.0