# [PATCH v6 02/11] clk: sunxi-ng: nkm: consider alternative parent rates when determining rate

From: Frank Oltmanns
Date: Mon Aug 07 2023 - 08:44:17 EST

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.

Acked-by: Maxime Ripard <mripard@xxxxxxxxxx>
Signed-off-by: Frank Oltmanns <frank@xxxxxxxxxxxx>
---
drivers/clk/sunxi-ng/ccu_nkm.c | 44 +++++++++++++++++++++++++++++++++++++++++-
1 file changed, 43 insertions(+), 1 deletion(-)

diff --git a/drivers/clk/sunxi-ng/ccu_nkm.c b/drivers/clk/sunxi-ng/ccu_nkm.c
index f267142e58b3..2f60f3c33e30 100644
--- a/drivers/clk/sunxi-ng/ccu_nkm.c
+++ b/drivers/clk/sunxi-ng/ccu_nkm.c
@@ -16,6 +16,45 @@ struct _ccu_nkm {
unsigned long m, min_m, max_m;
};

+static unsigned long ccu_nkm_find_best_with_parent_adj(struct clk_hw *parent_hw,
+ unsigned long *parent, unsigned long rate,
+ struct _ccu_nkm *nkm)
+{
+ unsigned long best_rate = 0, best_parent_rate = *parent, tmp_parent = *parent;
+ unsigned long best_n = 0, best_k = 0, best_m = 0;
+ unsigned long _n, _k, _m;
+
+ for (_k = nkm->min_k; _k <= nkm->max_k; _k++) {
+ for (_n = nkm->min_n; _n <= nkm->max_n; _n++) {
+ for (_m = nkm->min_m; _m <= nkm->max_m; _m++) {
+ unsigned long tmp_rate;
+
+ tmp_parent = clk_hw_round_rate(parent_hw, rate * _m / (_n * _k));
+
+ tmp_rate = tmp_parent * _n * _k / _m;
+ 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;
+ }
+ }
+ }
+ }
+
+ nkm->n = best_n;
+ nkm->k = best_k;
+ nkm->m = best_m;
+
+ *parent = best_parent_rate;
+
+ return best_rate;
+}
+
static unsigned long ccu_nkm_find_best(unsigned long parent, unsigned long rate,
struct _ccu_nkm *nkm)
{
@@ -124,7 +163,10 @@ 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);
+ else
+ rate = ccu_nkm_find_best_with_parent_adj(parent_hw, parent_rate, rate, &_nkm);

if (nkm->common.features & CCU_FEATURE_FIXED_POSTDIV)
rate /= nkm->fixed_post_div;

--
2.41.0