clk: renesas: rcar-gen2: Improve arithmetic divisions

- Use div64_ul() instead of div_u64() if the divisor is unsigned long,
    to avoid truncation to 32-bit on 64-bit platforms,
  - Prefer ULL constant suffixes over casts to u64,
  - Prioritize multiplication over division, to increase accuracy.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Link: https://lore.kernel.org/r/20190830134515.11925-2-geert+renesas@glider.be

diff --git a/drivers/clk/renesas/rcar-gen2-cpg.c b/drivers/clk/renesas/rcar-gen2-cpg.c
index f596a2dafcf4d8d1548b53ed506063f984578816..c378505830f0bacc6bc33a2798eac1bfe63e2ddf 100644 (file)
--- a/drivers/clk/renesas/rcar-gen2-cpg.c
+++ b/drivers/clk/renesas/rcar-gen2-cpg.c
@@ -72,10 +72,10 @@ static long cpg_z_clk_round_rate(struct clk_hw *hw, unsigned long rate,
        if (!prate)
                prate = 1;
 
-       mult = div_u64((u64)rate * 32, prate);
+       mult = div64_ul(rate * 32ULL, prate);
        mult = clamp(mult, 1U, 32U);
 
-       return *parent_rate / 32 * mult;
+       return div_u64((u64)*parent_rate * mult, 32);
 }
 
 static int cpg_z_clk_set_rate(struct clk_hw *hw, unsigned long rate,
@@ -86,7 +86,7 @@ static int cpg_z_clk_set_rate(struct clk_hw *hw, unsigned long rate,
        u32 val, kick;
        unsigned int i;
 
-       mult = div_u64((u64)rate * 32, parent_rate);
+       mult = div64_ul(rate * 32ULL, parent_rate);
        mult = clamp(mult, 1U, 32U);
 
        if (readl(zclk->kick_reg) & CPG_FRQCRB_KICK)