[linux-sunxi] [PATCH v5 02/12] clk: sunxi-ng: Use u64 for calculation of nkmp rate

[Jernej Skrabec]

When parent rate is 24MHz and multiplier N >= 180, intermediate clock
rate doesn't fit in 32 bit variable anymore.

Because of that, introduce function for calculating clock rate which
uses 64 bit variable for intermediate result.

Acked-by: Maxime Ripard <maxime.rip...@bootlin.com>
Signed-off-by: Jernej Skrabec <jernej.skra...@siol.net>
---
 drivers/clk/sunxi-ng/ccu_nkmp.c | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/drivers/clk/sunxi-ng/ccu_nkmp.c b/drivers/clk/sunxi-ng/ccu_nkmp.c
index a99068a08315..c3f6fe7be565 100644
--- a/drivers/clk/sunxi-ng/ccu_nkmp.c
+++ b/drivers/clk/sunxi-ng/ccu_nkmp.c
@@ -20,6 +20,18 @@ struct _ccu_nkmp {
        unsigned long   p, min_p, max_p;
 };
 
+static unsigned long ccu_nkmp_calc_rate(unsigned long parent,
+                                       unsigned long n, unsigned long k,
+                                       unsigned long m, unsigned long p)
+{
+       u64 rate = parent;
+
+       rate *= n * k;
+       do_div(rate, m * p);
+
+       return rate;
+}
+
 static void ccu_nkmp_find_best(unsigned long parent, unsigned long rate,
                               struct _ccu_nkmp *nkmp)
 {
@@ -33,7 +45,9 @@ static void ccu_nkmp_find_best(unsigned long parent, unsigned 
long rate,
                                for (_p = nkmp->min_p; _p <= nkmp->max_p; _p 
<<= 1) {
                                        unsigned long tmp_rate;
 
-                                       tmp_rate = parent * _n * _k / (_m * _p);
+                                       tmp_rate = ccu_nkmp_calc_rate(parent,
+                                                                     _n, _k,
+                                                                     _m, _p);
 
                                        if (tmp_rate > rate)
                                                continue;
@@ -107,7 +121,7 @@ static unsigned long ccu_nkmp_recalc_rate(struct clk_hw *hw,
        p = reg >> nkmp->p.shift;
        p &= (1 << nkmp->p.width) - 1;
 
-       return (parent_rate * n * k >> p) / m;
+       return ccu_nkmp_calc_rate(parent_rate, n, k, m, 1 << p);
 }
 
 static long ccu_nkmp_round_rate(struct clk_hw *hw, unsigned long rate,
@@ -127,7 +141,8 @@ static long ccu_nkmp_round_rate(struct clk_hw *hw, unsigned 
long rate,
 
        ccu_nkmp_find_best(*parent_rate, rate, &_nkmp);
 
-       return *parent_rate * _nkmp.n * _nkmp.k / (_nkmp.m * _nkmp.p);
+       return ccu_nkmp_calc_rate(*parent_rate, _nkmp.n, _nkmp.k,
+                                 _nkmp.m, _nkmp.p);
 }
 
 static int ccu_nkmp_set_rate(struct clk_hw *hw, unsigned long rate,
-- 
2.16.1

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