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authorLubomir Rintel <lkundrak@v3.sk>2020-05-20 00:41:39 +0200
committerStephen Boyd <sboyd@kernel.org>2020-05-27 17:55:11 -0700
commit06030c4e33babd63b6630d358a04f3dfb34cc29c (patch)
treedf09c8881092de255f1fec9faa08139a8d45b58d /drivers/clk
parent8f3d9f354286745c751374f5f1fcafee6b3f3136 (diff)
downloadlinux-06030c4e33babd63b6630d358a04f3dfb34cc29c.tar.bz2
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 <lkundrak@v3.sk> Link: https://lkml.kernel.org/r/20200519224151.2074597-2-lkundrak@v3.sk Signed-off-by: Stephen Boyd <sboyd@kernel.org>
Diffstat (limited to 'drivers/clk')
-rw-r--r--drivers/clk/mmp/clk-frac.c24
1 files changed, 16 insertions, 8 deletions
diff --git a/drivers/clk/mmp/clk-frac.c b/drivers/clk/mmp/clk-frac.c
index fabc09aca6c4..ed9928f5bdc7 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;
}