[PATCH 1/1] clk: nuvoton: ma35d1-divider: use direct formula instead of divider table

[Joey Lu <a0987203069@gmail.com>]

The ADC clock divider register implements a simple closed-form relation,
rate = parent_rate / (2 * (N + 1)), but it was previously modeled by
building a clk_div_table with one entry per possible divider value (up
to 2^width entries) and feeding it through the generic
divider_recalc_rate()/divider_determine_rate()/divider_get_val() helpers.
This is unnecessarily expensive (a large table allocation and a linear
scan on every rate lookup) for what is just a closed-form expression.

Also drop the mask_bit/mask mechanism: the previous code unconditionally
OR'd an arbitrary bit into the divider register on every set_rate() call.
The one existing caller passed mask_bit as a bitmask value (0x1ffff)
rather than a bit index, which BIT() then shifted by an out-of-range
amount, undefined behavior. Since the divider field write already clears
and rewrites only its own bits, no extra forced bit is required, so the
parameter is removed entirely.

Compute the divisor directly in recalc_rate()/determine_rate()/set_rate()
instead, with explicit range clamping and a rate == 0 guard.

Fixes: 691521a367cf ("clk: nuvoton: Add clock driver for ma35d1 clock controller")
Signed-off-by: Joey Lu <a0987203069@gmail.com>
---
 drivers/clk/nuvoton/clk-ma35d1-divider.c | 73 +++++++++++-------------
 drivers/clk/nuvoton/clk-ma35d1.c         |  2 +-
 drivers/clk/nuvoton/clk-ma35d1.h         |  2 +-
 3 files changed, 36 insertions(+), 41 deletions(-)

diff --git a/drivers/clk/nuvoton/clk-ma35d1-divider.c b/drivers/clk/nuvoton/clk-ma35d1-divider.c
index e992e7c30341..03fcf87caae1 100644
--- a/drivers/clk/nuvoton/clk-ma35d1-divider.c
+++ b/drivers/clk/nuvoton/clk-ma35d1-divider.c
@@ -16,8 +16,6 @@ struct ma35d1_adc_clk_div {
 	void __iomem *reg;
 	u8 shift;
 	u8 width;
-	u32 mask;
-	const struct clk_div_table *table;
 	/* protects concurrent access to clock divider registers */
 	spinlock_t *lock;
 };
@@ -29,44 +27,60 @@ static inline struct ma35d1_adc_clk_div *to_ma35d1_adc_clk_div(struct clk_hw *_h
 
 static unsigned long ma35d1_clkdiv_recalc_rate(struct clk_hw *hw, unsigned long parent_rate)
 {
-	unsigned int val;
 	struct ma35d1_adc_clk_div *dclk = to_ma35d1_adc_clk_div(hw);
+	unsigned int val;
 
 	val = readl_relaxed(dclk->reg) >> dclk->shift;
 	val &= clk_div_mask(dclk->width);
-	val += 1;
-	return divider_recalc_rate(hw, parent_rate, val, dclk->table,
-				   CLK_DIVIDER_ROUND_CLOSEST, dclk->width);
+
+	return DIV_ROUND_CLOSEST_ULL((u64)parent_rate, 2 * (val + 1));
 }
 
 static int ma35d1_clkdiv_determine_rate(struct clk_hw *hw,
 					struct clk_rate_request *req)
 {
 	struct ma35d1_adc_clk_div *dclk = to_ma35d1_adc_clk_div(hw);
+	unsigned int val;
+
+	if (!req->rate)
+		return -EINVAL;
 
-	return divider_determine_rate(hw, req, dclk->table, dclk->width,
-				      CLK_DIVIDER_ROUND_CLOSEST);
+	val = DIV_ROUND_UP(req->best_parent_rate, 2 * req->rate);
+	if (val == 0)
+		val = 1;
+	if (val > (unsigned int)clk_div_mask(dclk->width) + 1)
+		val = clk_div_mask(dclk->width) + 1;
+
+	req->rate = DIV_ROUND_CLOSEST_ULL((u64)req->best_parent_rate, 2 * val);
+
+	return 0;
 }
 
 static int ma35d1_clkdiv_set_rate(struct clk_hw *hw, unsigned long rate, unsigned long parent_rate)
 {
-	int value;
-	unsigned long flags = 0;
-	u32 data;
 	struct ma35d1_adc_clk_div *dclk = to_ma35d1_adc_clk_div(hw);
+	unsigned long flags;
+	unsigned int val;
+	u32 data;
+
+	if (!rate)
+		return -EINVAL;
 
-	value = divider_get_val(rate, parent_rate, dclk->table,
-				dclk->width, CLK_DIVIDER_ROUND_CLOSEST);
+	val = DIV_ROUND_UP(parent_rate, 2 * rate);
+	if (val == 0)
+		val = 1;
+	if (val > (unsigned int)clk_div_mask(dclk->width) + 1)
+		val = clk_div_mask(dclk->width) + 1;
 
 	spin_lock_irqsave(dclk->lock, flags);
 
 	data = readl_relaxed(dclk->reg);
 	data &= ~(clk_div_mask(dclk->width) << dclk->shift);
-	data |= (value - 1) << dclk->shift;
-	data |= dclk->mask;
+	data |= (val - 1) << dclk->shift;
 	writel_relaxed(data, dclk->reg);
 
 	spin_unlock_irqrestore(dclk->lock, flags);
+
 	return 0;
 }
 
@@ -79,39 +93,21 @@ static const struct clk_ops ma35d1_adc_clkdiv_ops = {
 struct clk_hw *ma35d1_reg_adc_clkdiv(struct device *dev, const char *name,
 				     struct clk_hw *parent_hw, spinlock_t *lock,
 				     unsigned long flags, void __iomem *reg,
-				     u8 shift, u8 width, u32 mask_bit)
+				     u8 shift, u8 width)
 {
-	struct ma35d1_adc_clk_div *div;
-	struct clk_init_data init;
-	struct clk_div_table *table;
 	struct clk_parent_data pdata = { .index = 0 };
-	u32 max_div, min_div;
+	struct ma35d1_adc_clk_div *div;
+	struct clk_init_data init = {};
 	struct clk_hw *hw;
 	int ret;
-	int i;
 
 	div = devm_kzalloc(dev, sizeof(*div), GFP_KERNEL);
 	if (!div)
 		return ERR_PTR(-ENOMEM);
 
-	max_div = clk_div_mask(width) + 1;
-	min_div = 1;
-
-	table = devm_kcalloc(dev, max_div + 1, sizeof(*table), GFP_KERNEL);
-	if (!table)
-		return ERR_PTR(-ENOMEM);
-
-	for (i = 0; i < max_div; i++) {
-		table[i].val = min_div + i;
-		table[i].div = 2 * table[i].val;
-	}
-	table[max_div].val = 0;
-	table[max_div].div = 0;
-
-	memset(&init, 0, sizeof(init));
 	init.name = name;
 	init.ops = &ma35d1_adc_clkdiv_ops;
-	init.flags |= flags;
+	init.flags = flags;
 	pdata.hw = parent_hw;
 	init.parent_data = &pdata;
 	init.num_parents = 1;
@@ -119,15 +115,14 @@ struct clk_hw *ma35d1_reg_adc_clkdiv(struct device *dev, const char *name,
 	div->reg = reg;
 	div->shift = shift;
 	div->width = width;
-	div->mask = mask_bit ? BIT(mask_bit) : 0;
 	div->lock = lock;
 	div->hw.init = &init;
-	div->table = table;
 
 	hw = &div->hw;
 	ret = devm_clk_hw_register(dev, hw);
 	if (ret)
 		return ERR_PTR(ret);
+
 	return hw;
 }
 EXPORT_SYMBOL_GPL(ma35d1_reg_adc_clkdiv);
diff --git a/drivers/clk/nuvoton/clk-ma35d1.c b/drivers/clk/nuvoton/clk-ma35d1.c
index 9f65d0623517..f91a8369a2bc 100644
--- a/drivers/clk/nuvoton/clk-ma35d1.c
+++ b/drivers/clk/nuvoton/clk-ma35d1.c
@@ -1017,7 +1017,7 @@ static int ma35d1_clocks_probe(struct platform_device *pdev)
 	hws[ADC_DIV] = ma35d1_reg_adc_clkdiv(dev, "adc_div", hws[PCLK0],
 					     &ma35d1_lock, 0,
 					     clk_base + REG_CLK_CLKDIV4,
-					     4, 17, 0x1ffff);
+					     4, 17);
 	hws[ADC_GATE] = ma35d1_clk_gate(dev, "adc_gate", "adc_div",
 					clk_base + REG_CLK_APBCLK2, 24);
 
diff --git a/drivers/clk/nuvoton/clk-ma35d1.h b/drivers/clk/nuvoton/clk-ma35d1.h
index 3adee440f60a..1fdcd4658b5f 100644
--- a/drivers/clk/nuvoton/clk-ma35d1.h
+++ b/drivers/clk/nuvoton/clk-ma35d1.h
@@ -13,6 +13,6 @@ struct clk_hw *ma35d1_reg_clk_pll(struct device *dev, u32 id, u8 u8mode, const c
 struct clk_hw *ma35d1_reg_adc_clkdiv(struct device *dev, const char *name,
 				     struct clk_hw *parent_hw, spinlock_t *lock,
 				     unsigned long flags, void __iomem *reg,
-				     u8 shift, u8 width, u32 mask_bit);
+				     u8 shift, u8 width);
 
 #endif /* __DRV_CLK_NUVOTON_MA35D1_H */
-- 
2.43.0