[PATCH 1/2] clk: sunxi-ng: nkm: consider alternative parent rates when finding rate

[Frank Oltmanns <frank@oltmanns.dev>]

In case the CLK_SET_RATE_PARENT flag is set, consider using a different
parent rate when determining a new rate.

To find the best match for the requested rate, perform the following
steps for each NKM combination:
 - calculate the optimal parent rate,
 - find the best parent rate that the parent clock actually supports
 - use that parent rate to calculate the effective rate.

In case the clk does not support setting the parent rate, use the same
algorithm as before.

Signed-off-by: Frank Oltmanns <frank@oltmanns.dev>
---
 drivers/clk/sunxi-ng/ccu_nkm.c | 40 ++++++++++++++++++++++++++--------
 1 file changed, 31 insertions(+), 9 deletions(-)

diff --git a/drivers/clk/sunxi-ng/ccu_nkm.c b/drivers/clk/sunxi-ng/ccu_nkm.c
index a0978a50edae..c71e237226f2 100644
--- a/drivers/clk/sunxi-ng/ccu_nkm.c
+++ b/drivers/clk/sunxi-ng/ccu_nkm.c
@@ -16,10 +16,10 @@ struct _ccu_nkm {
 	unsigned long	m, min_m, max_m;
 };
 
-static unsigned long ccu_nkm_find_best(unsigned long parent, unsigned long rate,
-				       struct _ccu_nkm *nkm)
+static unsigned long ccu_nkm_find_best(unsigned long *parent, unsigned long rate,
+				       struct _ccu_nkm *nkm, struct clk_hw *parent_hw)
 {
-	unsigned long best_rate = 0;
+	unsigned long best_rate = 0, best_parent_rate = 0, tmp_parent = *parent;
 	unsigned long best_n = 0, best_k = 0, best_m = 0;
 	unsigned long _n, _k, _m;
 
@@ -28,12 +28,29 @@ static unsigned long ccu_nkm_find_best(unsigned long parent, unsigned long rate,
 			for (_m = nkm->min_m; _m <= nkm->max_m; _m++) {
 				unsigned long tmp_rate;
 
-				tmp_rate = parent * _n * _k / _m;
+				if (parent_hw) {
+					// We must round up the desired parent rate, because the
+					// rounding down happens when calculating tmp_rate. If we
+					// round down also here, we'd round down twice.
+					unsigned long optimal_parent =
+							(rate * _m + (_n * _k - 1)) / _n / _k;
+
+					tmp_parent = clk_hw_round_rate(parent_hw, optimal_parent);
+
+					// if the optimal parent rate is below the minimum rate of
+					// the parent ignore this combination
+					if (tmp_parent > optimal_parent)
+						continue;
+					tmp_rate = tmp_parent * _n * _k / _m;
+				} else {
+					tmp_rate = tmp_parent * _n * _k / _m;
+					if (tmp_rate > rate)
+						continue;
+				}
 
-				if (tmp_rate > rate)
-					continue;
 				if ((rate - tmp_rate) < (rate - best_rate)) {
 					best_rate = tmp_rate;
+					best_parent_rate = tmp_parent;
 					best_n = _n;
 					best_k = _k;
 					best_m = _m;
@@ -46,6 +63,8 @@ static unsigned long ccu_nkm_find_best(unsigned long parent, unsigned long rate,
 	nkm->k = best_k;
 	nkm->m = best_m;
 
+	*parent = best_parent_rate;
+
 	return best_rate;
 }
 
@@ -106,7 +125,7 @@ static unsigned long ccu_nkm_recalc_rate(struct clk_hw *hw,
 }
 
 static unsigned long ccu_nkm_round_rate(struct ccu_mux_internal *mux,
-					struct clk_hw *hw,
+					struct clk_hw *parent_hw,
 					unsigned long *parent_rate,
 					unsigned long rate,
 					void *data)
@@ -124,7 +143,10 @@ static unsigned long ccu_nkm_round_rate(struct ccu_mux_internal *mux,
 	if (nkm->common.features & CCU_FEATURE_FIXED_POSTDIV)
 		rate *= nkm->fixed_post_div;
 
-	rate = ccu_nkm_find_best(*parent_rate, rate, &_nkm);
+	if (!clk_hw_can_set_rate_parent(&nkm->common.hw))
+		rate = ccu_nkm_find_best(parent_rate, rate, &_nkm, NULL);
+	else
+		rate = ccu_nkm_find_best(parent_rate, rate, &_nkm, parent_hw);
 
 	if (nkm->common.features & CCU_FEATURE_FIXED_POSTDIV)
 		rate /= nkm->fixed_post_div;
@@ -159,7 +181,7 @@ static int ccu_nkm_set_rate(struct clk_hw *hw, unsigned long rate,
 	_nkm.min_m = 1;
 	_nkm.max_m = nkm->m.max ?: 1 << nkm->m.width;
 
-	ccu_nkm_find_best(parent_rate, rate, &_nkm);
+	ccu_nkm_find_best(&parent_rate, rate, &_nkm, NULL);
 
 	spin_lock_irqsave(nkm->common.lock, flags);
 
-- 
2.40.1