[PATCH v2 0/3] clk: nuvoton: ma35d1: fix PLL frequency calculation

[PATCH v2 0/3] clk: nuvoton: ma35d1: fix PLL frequency calculation

[Joey Lu]

Fix four bugs in the MA35D1 PLL clock driver that cause incorrect
frequency values returned from recalc_rate() and determine_rate().

v1 combined all fixes into a single commit.  At reviewer request,
split into one patch per logical fix:

  1/3 - fix div_u64 return value being discarded (affects both
        ma35d1_calc_smic_pll_freq and ma35d1_calc_pll_freq INT mode)

  2/3 - fix PLL_CTL1_FRAC mask width (8-bit -> 24-bit) and update
        the fractional-mode arithmetic accordingly

  3/3 - fix ma35d1_clk_pll_determine_rate: move find_closest() into
        the configurable-PLL branch; unify read-only PLL handling

Joey Lu (3):
  clk: nuvoton: ma35d1: fix ignored div_u64 return values in PLL freq
    calculation
  clk: nuvoton: ma35d1: fix PLL_CTL1_FRAC bit field width and fractional
    calc
  clk: nuvoton: ma35d1: fix ma35d1_clk_pll_determine_rate logic

 drivers/clk/nuvoton/clk-ma35d1-pll.c | 38 ++++++++++++++--------------
 1 file changed, 19 insertions(+), 19 deletions(-)

-- 
2.43.0

[PATCH v2 1/3] clk: nuvoton: ma35d1: fix ignored div_u64 return values in PLL freq calculation

[Joey Lu]

div_u64() does not modify its argument in place; the return value must
be assigned.  Both ma35d1_calc_smic_pll_freq() and ma35d1_calc_pll_freq()
called div_u64() and discarded the result, leaving pll_freq holding the
undivided product and thus returning a frequency orders of magnitude too
high.

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 | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/clk/nuvoton/clk-ma35d1-pll.c b/drivers/clk/nuvoton/clk-ma35d1-pll.c
index 4620acfe47e8..bfedd45bd04b 100644
--- a/drivers/clk/nuvoton/clk-ma35d1-pll.c
+++ b/drivers/clk/nuvoton/clk-ma35d1-pll.c
@@ -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;
 }
 
@@ -110,7 +110,7 @@ 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) */
-- 
2.43.0

[PATCH v2 2/3] clk: nuvoton: ma35d1: fix PLL_CTL1_FRAC bit field width and fractional calc

[Joey Lu]

PLL_CTL1_FRAC was defined as GENMASK(31, 24), covering only 8 bits.
The hardware fractional field occupies bits [31:8] (24 bits), so the
mask must be GENMASK(31, 8).

The previous fractional-mode calculation used FIELD_MAX(PLL_CTL1_FRAC)
as the denominator to obtain 2 decimal places.  With the corrected 24-bit
mask the old divisor is wrong; replace the arithmetic with a proper
24-bit fixed-point rounding to 3 decimal places:

  n_frac = n * 1000 + (x * 1000 + 500) >> 24

The +500 term provides round-to-nearest before the right shift.

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 | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/clk/nuvoton/clk-ma35d1-pll.c b/drivers/clk/nuvoton/clk-ma35d1-pll.c
index bfedd45bd04b..7e6b30d20c01 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
@@ -113,9 +113,9 @@ static unsigned long ma35d1_calc_pll_freq(u8 mode, u32 *reg_ctl, unsigned long 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;
 }
-- 
2.43.0

[PATCH v2 3/3] clk: nuvoton: ma35d1: fix ma35d1_clk_pll_determine_rate logic

[Joey Lu]

ma35d1_clk_pll_determine_rate() called ma35d1_pll_find_closest()
unconditionally before the switch statement, and then every case
branch overwrote pll_freq by reading the current hardware registers.
For CAPLL and DDRPLL this means find_closest() ran unnecessarily
(and incorrectly, since those PLLs are read-only) and its result
was silently discarded.

Fix by moving the find_closest() call inside the APLL/EPLL/VPLL
branch where it belongs.  Group CAPLL and DDRPLL together as
read-only PLLs that simply report their current rate; handle them
with an explicit if/else to keep the CAPLL (SMIC design) and DDRPLL
(standard design) paths distinct.

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 | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/drivers/clk/nuvoton/clk-ma35d1-pll.c b/drivers/clk/nuvoton/clk-ma35d1-pll.c
index 7e6b30d20c01..314b81e7727c 100644
--- a/drivers/clk/nuvoton/clk-ma35d1-pll.c
+++ b/drivers/clk/nuvoton/clk-ma35d1-pll.c
@@ -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;
 }
 
-- 
2.43.0