From 06030c4e33babd63b6630d358a04f3dfb34cc29c Mon Sep 17 00:00:00 2001 From: Lubomir Rintel Date: Wed, 20 May 2020 00:41:39 +0200 Subject: [PATCH] clk: mmp: frac: Do not lose last 4 digits of precision While calculating the output rate of a fractional divider clock, the value is divided and multipled by 10000, discarding the least significant digits -- presumably to fit the intermediate value within 32 bits. The precision we're losing is, however, not insignificant for things like I2S clock. Maybe also elsewhere, now that since commit ea56ad60260e ("clk: mmp2: Stop pretending PLL outputs are constant") the parent rates are more precise and no longer rounded to 10000s. Signed-off-by: Lubomir Rintel Link: https://lkml.kernel.org/r/20200519224151.2074597-2-lkundrak@v3.sk Signed-off-by: Stephen Boyd --- drivers/clk/mmp/clk-frac.c | 24 ++++++++++++++++-------- 1 file changed, 16 insertions(+), 8 deletions(-) diff --git a/drivers/clk/mmp/clk-frac.c b/drivers/clk/mmp/clk-frac.c index fabc09ac..ed9928f 100644 --- a/drivers/clk/mmp/clk-frac.c +++ b/drivers/clk/mmp/clk-frac.c @@ -28,13 +28,15 @@ static long clk_factor_round_rate(struct clk_hw *hw, unsigned long drate, unsigned long *prate) { struct mmp_clk_factor *factor = to_clk_factor(hw); - unsigned long rate = 0, prev_rate; + u64 rate = 0, prev_rate; int i; for (i = 0; i < factor->ftbl_cnt; i++) { prev_rate = rate; - rate = (((*prate / 10000) * factor->ftbl[i].den) / - (factor->ftbl[i].num * factor->masks->factor)) * 10000; + rate = *prate; + rate *= factor->ftbl[i].den; + do_div(rate, factor->ftbl[i].num * factor->masks->factor); + if (rate > drate) break; } @@ -54,6 +56,7 @@ static unsigned long clk_factor_recalc_rate(struct clk_hw *hw, struct mmp_clk_factor *factor = to_clk_factor(hw); struct mmp_clk_factor_masks *masks = factor->masks; unsigned int val, num, den; + u64 rate; val = readl_relaxed(factor->base); @@ -66,8 +69,11 @@ static unsigned long clk_factor_recalc_rate(struct clk_hw *hw, if (!den) return 0; - return (((parent_rate / 10000) * den) / - (num * factor->masks->factor)) * 10000; + rate = parent_rate; + rate *= den; + do_div(rate, num * factor->masks->factor); + + return rate; } /* Configures new clock rate*/ @@ -78,12 +84,14 @@ static int clk_factor_set_rate(struct clk_hw *hw, unsigned long drate, struct mmp_clk_factor_masks *masks = factor->masks; int i; unsigned long val; - unsigned long rate = 0; unsigned long flags = 0; + u64 rate = 0; for (i = 0; i < factor->ftbl_cnt; i++) { - rate = (((prate / 10000) * factor->ftbl[i].den) / - (factor->ftbl[i].num * factor->masks->factor)) * 10000; + rate = prate; + rate *= factor->ftbl[i].den; + do_div(rate, factor->ftbl[i].num * factor->masks->factor); + if (rate > drate) break; } -- 2.7.4