[PATCH 1/5] clk: sunxi-ng: nkm: Support constraints on m/n ratio and parent rate

[Frank Oltmanns]

The Allwinner A64 manual lists the following constraints for the
PLL-MIPI clock:
 - M/N >= 3
 - (PLL_VIDEO0)/M >= 24MHz

The PLL-MIPI clock is implemented as ccu_nkm. Therefore, add support for
these constraints.

Signed-off-by: Frank Oltmanns <fr...@oltmanns.dev>
---
 drivers/clk/sunxi-ng/ccu_nkm.c | 23 +++++++++++++++++++++++
 drivers/clk/sunxi-ng/ccu_nkm.h |  8 ++++++++
 2 files changed, 31 insertions(+)

diff --git a/drivers/clk/sunxi-ng/ccu_nkm.c b/drivers/clk/sunxi-ng/ccu_nkm.c
index eed64547ad42..2af5c1ebd527 100644
--- a/drivers/clk/sunxi-ng/ccu_nkm.c
+++ b/drivers/clk/sunxi-ng/ccu_nkm.c
@@ -16,6 +16,20 @@ struct _ccu_nkm {
        unsigned long   m, min_m, max_m;
 };
 
+static bool ccu_nkm_is_valid_rate(struct ccu_common *common, unsigned long 
parent,
+                                 unsigned long n, unsigned long m)
+{
+       struct ccu_nkm *nkm = container_of(common, struct ccu_nkm, common);
+
+       if (nkm->max_mn_ratio && (m > nkm->max_mn_ratio * n))
+               return false;
+
+       if (nkm->parent_wo_nk && (parent < nkm->parent_wo_nk * m))
+               return false;
+
+       return true;
+}
+
 static unsigned long ccu_nkm_find_best_with_parent_adj(struct ccu_common 
*common,
                                                       struct clk_hw *parent_hw,
                                                       unsigned long *parent, 
unsigned long rate,
@@ -32,6 +46,9 @@ static unsigned long ccu_nkm_find_best_with_parent_adj(struct 
ccu_common *common
 
                                tmp_parent = clk_hw_round_rate(parent_hw, rate 
* _m / (_n * _k));
 
+                               if (!ccu_nkm_is_valid_rate(common, tmp_parent, 
_n, _m))
+                                       continue;
+
                                tmp_rate = tmp_parent * _n * _k / _m;
 
                                if (ccu_is_better_rate(common, rate, tmp_rate, 
best_rate) ||
@@ -65,6 +82,12 @@ static unsigned long ccu_nkm_find_best(unsigned long parent, 
unsigned long rate,
        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++) {
+                               if ((common->reg == 0x040) && (_m > 3 * _n))
+                                       break;
+
+                               if ((common->reg == 0x040) && (parent < 
24000000 * _m))
+                                       continue;
+
                                unsigned long tmp_rate;
 
                                tmp_rate = parent * _n * _k / _m;
diff --git a/drivers/clk/sunxi-ng/ccu_nkm.h b/drivers/clk/sunxi-ng/ccu_nkm.h
index 6601defb3f38..d3d3eaf55faf 100644
--- a/drivers/clk/sunxi-ng/ccu_nkm.h
+++ b/drivers/clk/sunxi-ng/ccu_nkm.h
@@ -16,6 +16,12 @@
  * struct ccu_nkm - Definition of an N-K-M clock
  *
  * Clocks based on the formula parent * N * K / M
+ *
+ * @max_mn_ratio:      Maximum value for M / N.
+ * @parent_wo_nk:      The minimum rate the parent must provide after applying 
the divisor,
+ *                     but without applying the multipliers, i.e. the 
contstraint
+ *                        (parent rate)/M >= parent_wo_nk
+ *                     must be fulfilled.
  */
 struct ccu_nkm {
        u32                     enable;
@@ -27,6 +33,8 @@ struct ccu_nkm {
        struct ccu_mux_internal mux;
 
        unsigned int            fixed_post_div;
+       unsigned long           max_mn_ratio;
+       unsigned long           parent_wo_nk;
 
        struct ccu_common       common;
 };

-- 
2.43.0