[PATCH 1/1] clk: nuvoton: ma35d1: fix PLL frequency calculation

[Joey Lu <a0987203069@gmail.com>]

Fix four bugs in the MA35D1 PLL driver:

1. PLL_CTL1_FRAC was defined as GENMASK(31, 24) (8 bits), but the
   hardware fractional field spans bits [31:8] (24 bits). This caused
   wrong frequency calculation in fractional and spread-spectrum modes.

2. div_u64() does not modify its argument in-place; the quotient must
   be assigned from the return value. Both ma35d1_calc_smic_pll_freq()
   and ma35d1_calc_pll_freq() discarded the return value, leaving
   pll_freq undivided and orders of magnitude too high.

3. The fractional-mode calculation divided x by FIELD_MAX(PLL_CTL1_FRAC)
   to get 2 decimal digits. After correcting the mask to 24 bits, update
   the arithmetic to use 3 decimal digits with proper 24-bit fixed-point
   rounding.

4. ma35d1_clk_pll_determine_rate() called ma35d1_pll_find_closest()
   unconditionally before the switch, but then overwrote its result by
   reading the current hardware registers for every PLL type. Move the
   find_closest() call inside the configurable-PLL branch (APLL, EPLL,
   VPLL). CAPLL and DDRPLL do not support runtime rate changes and
   correctly return the current hardware rate.

Fixes: 691521a367cf ("clk: nuvoton: Add clock driver for ma35d1 clock controller")
Signed-off-by: Joey Lu <a0987203069@gmail.com>
---
 drivers/clk/nuvoton/clk-ma35d1-pll.c | 34 +++++++++++++--------------
 1 file changed, 17 insertions(+), 17 deletions(-)

diff --git a/drivers/clk/nuvoton/clk-ma35d1-pll.c b/drivers/clk/nuvoton/clk-ma35d1-pll.c
index 4620acfe47e8..314b81e7727c 100644
--- a/drivers/clk/nuvoton/clk-ma35d1-pll.c
+++ b/drivers/clk/nuvoton/clk-ma35d1-pll.c
@@ -48,7 +48,7 @@
 #define PLL_CTL1_PD		BIT(0)
 #define PLL_CTL1_BP		BIT(1)
 #define PLL_CTL1_OUTDIV		GENMASK(6, 4)
-#define PLL_CTL1_FRAC		GENMASK(31, 24)
+#define PLL_CTL1_FRAC		GENMASK(31, 8)
 #define PLL_CTL2_SLOPE		GENMASK(23, 0)
 
 #define INDIV_MIN		1
@@ -92,7 +92,7 @@ static unsigned long ma35d1_calc_smic_pll_freq(u32 pll0_ctl0,
 	p = FIELD_GET(SPLL0_CTL0_OUTDIV, pll0_ctl0);
 	outdiv = 1 << p;
 	pll_freq = (u64)parent_rate * n;
-	div_u64(pll_freq, m * outdiv);
+	pll_freq = div_u64(pll_freq, m * outdiv);
 	return pll_freq;
 }
 
@@ -110,12 +110,12 @@ static unsigned long ma35d1_calc_pll_freq(u8 mode, u32 *reg_ctl, unsigned long p
 
 	if (mode == PLL_MODE_INT) {
 		pll_freq = (u64)parent_rate * n;
-		div_u64(pll_freq, m * p);
+		pll_freq = div_u64(pll_freq, m * p);
 	} else {
 		x = FIELD_GET(PLL_CTL1_FRAC, reg_ctl[1]);
-		/* 2 decimal places floating to integer (ex. 1.23 to 123) */
-		n = n * 100 + ((x * 100) / FIELD_MAX(PLL_CTL1_FRAC));
-		pll_freq = div_u64(parent_rate * n, 100 * m * p);
+		/* x is 24-bit fractional part, convert to 3 decimal digits */
+		n = n * 1000 + (u32)(((u64)x * 1000 + 500) >> 24);
+		pll_freq = div_u64((u64)parent_rate * n, 1000 * m * p);
 	}
 	return pll_freq;
 }
@@ -255,32 +255,32 @@ static int ma35d1_clk_pll_determine_rate(struct clk_hw *hw,
 	if (req->best_parent_rate < PLL_FREF_MIN_FREQ || req->best_parent_rate > PLL_FREF_MAX_FREQ)
 		return -EINVAL;
 
-	ret = ma35d1_pll_find_closest(pll, req->rate, req->best_parent_rate,
-				      reg_ctl, &pll_freq);
-	if (ret < 0)
-		return ret;
-
 	switch (pll->id) {
 	case CAPLL:
+	case DDRPLL:
+		/* Read-only PLLs: return current rate */
 		reg_ctl[0] = readl_relaxed(pll->ctl0_base);
-		pll_freq = ma35d1_calc_smic_pll_freq(reg_ctl[0], req->best_parent_rate);
+		if (pll->id == CAPLL) {
+			pll_freq = ma35d1_calc_smic_pll_freq(reg_ctl[0], req->best_parent_rate);
+		} else {
+			reg_ctl[1] = readl_relaxed(pll->ctl1_base);
+			pll_freq = ma35d1_calc_pll_freq(pll->mode, reg_ctl, req->best_parent_rate);
+		}
 		req->rate = pll_freq;
-
 		return 0;
-	case DDRPLL:
 	case APLL:
 	case EPLL:
 	case VPLL:
-		reg_ctl[0] = readl_relaxed(pll->ctl0_base);
-		reg_ctl[1] = readl_relaxed(pll->ctl1_base);
-		pll_freq = ma35d1_calc_pll_freq(pll->mode, reg_ctl, req->best_parent_rate);
+		/* Configurable PLLs: find closest achievable rate */
+		ret = ma35d1_pll_find_closest(pll, req->rate, req->best_parent_rate,
+					      reg_ctl, &pll_freq);
+		if (ret < 0)
+			return ret;
 		req->rate = pll_freq;
-
 		return 0;
 	}
 
 	req->rate = 0;
-
 	return 0;
 }
 
-- 
2.49.0