clk: divider: Add round to closest divider

In some cases, we want to be able to round the divider to the closest one,
instead than rounding up.

This patch adds a new CLK_DIVIDER_ROUND_CLOSEST flag to specify the divider
has to round to closest div, keeping rounding up as de default behaviour.

Signed-off-by: Maxime Coquelin <maxime.coquelin@st.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>

1 files changed, 67 insertions, 2 deletions

diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c
index 4637697c139f..c57294563a98 100644
--- a/drivers/clk/clk-divider.c
+++ b/drivers/clk/clk-divider.c
@@ -43,6 +43,17 @@ static unsigned int _get_table_maxdiv(const struct clk_div_table *table)
         return maxdiv;
 }
 
+static unsigned int _get_table_mindiv(const struct clk_div_table *table)
+{
+        unsigned int mindiv = UINT_MAX;
+        const struct clk_div_table *clkt;
+
+        for (clkt = table; clkt->div; clkt++)
+                if (clkt->div < mindiv)
+                        mindiv = clkt->div;
+        return mindiv;
+}
+
 static unsigned int _get_maxdiv(struct clk_divider *divider)
 {
         if (divider->flags & CLK_DIVIDER_ONE_BASED)
@@ -162,6 +173,24 @@ static int _round_up_table(const struct clk_div_table *table, int div)
         return up;
 }
 
+static int _round_down_table(const struct clk_div_table *table, int div)
+{
+        const struct clk_div_table *clkt;
+        int down = _get_table_mindiv(table);
+
+        for (clkt = table; clkt->div; clkt++) {
+                if (clkt->div == div)
+                        return clkt->div;
+                else if (clkt->div > div)
+                        continue;
+
+                if ((div - clkt->div) < (div - down))
+                        down = clkt->div;
+        }
+
+        return down;
+}
+
 static int _div_round_up(struct clk_divider *divider,
                 unsigned long parent_rate, unsigned long rate)
 {
@@ -175,6 +204,42 @@ static int _div_round_up(struct clk_divider *divider,
         return div;
 }
 
+static int _div_round_closest(struct clk_divider *divider,
+                unsigned long parent_rate, unsigned long rate)
+{
+        int up, down, div;
+
+        up = down = div = DIV_ROUND_CLOSEST(parent_rate, rate);
+
+        if (divider->flags & CLK_DIVIDER_POWER_OF_TWO) {
+                up = __roundup_pow_of_two(div);
+                down = __rounddown_pow_of_two(div);
+        } else if (divider->table) {
+                up = _round_up_table(divider->table, div);
+                down = _round_down_table(divider->table, div);
+        }
+
+        return (up - div) <= (div - down) ? up : down;
+}
+
+static int _div_round(struct clk_divider *divider, unsigned long parent_rate,
+                unsigned long rate)
+{
+        if (divider->flags & CLK_DIVIDER_ROUND_CLOSEST)
+                return _div_round_closest(divider, parent_rate, rate);
+
+        return _div_round_up(divider, parent_rate, rate);
+}
+
+static bool _is_best_div(struct clk_divider *divider,
+                int rate, int now, int best)
+{
+        if (divider->flags & CLK_DIVIDER_ROUND_CLOSEST)
+                return abs(rate - now) < abs(rate - best);
+
+        return now <= rate && now > best;
+}
+
 static int clk_divider_bestdiv(struct clk_hw *hw, unsigned long rate,
                 unsigned long *best_parent_rate)
 {
@@ -190,7 +255,7 @@ static int clk_divider_bestdiv(struct clk_hw *hw, unsigned long rate,
 
         if (!(__clk_get_flags(hw->clk) & CLK_SET_RATE_PARENT)) {
                 parent_rate = *best_parent_rate;
-                bestdiv = _div_round_up(divider, parent_rate, rate);
+                bestdiv = _div_round(divider, parent_rate, rate);
                 bestdiv = bestdiv == 0 ? 1 : bestdiv;
                 bestdiv = bestdiv > maxdiv ? maxdiv : bestdiv;
                 return bestdiv;
@@ -217,7 +282,7 @@ static int clk_divider_bestdiv(struct clk_hw *hw, unsigned long rate,
                 parent_rate = __clk_round_rate(__clk_get_parent(hw->clk),
                                 MULT_ROUND_UP(rate, i));
                 now = DIV_ROUND_UP(parent_rate, i);
-                if (now <= rate && now > best) {
+                if (_is_best_div(divider, rate, now, best)) {
                         bestdiv = i;
                         best = now;
                         *best_parent_rate = parent_rate;