clk: stm32f4: use FIELD helpers to access the PLLCFGR fields

Use GENMASK() along with FIELD_GET() and FIELD_PREP() helpers to access
the PLLCFGR fields instead of manually masking and shifting.

Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Link: https://lore.kernel.org/r/20250114182021.670435-4-dario.binacchi@amarulasolutions.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/clk-stm32f4.c

@@ -5,6 +5,7 @@
  * Inspired by clk-asm9260.c .
  */
 
+#include <linux/bitfield.h>
 #include <linux/clk-provider.h>
 #include <linux/err.h>
 #include <linux/io.h>
@@ -39,6 +40,8 @@
 #define STM32F4_RCC_DCKCFGR		0x8c
 #define STM32F7_RCC_DCKCFGR2		0x90
 
+#define STM32F4_RCC_PLLCFGR_N_MASK	GENMASK(14, 6)
+
 #define NONE -1
 #define NO_IDX  NONE
 #define NO_MUX  NONE
@@ -632,9 +635,11 @@ static unsigned long stm32f4_pll_recalc(struct clk_hw *hw,
 {
 	struct clk_gate *gate = to_clk_gate(hw);
 	struct stm32f4_pll *pll = to_stm32f4_pll(gate);
+	unsigned long val;
 	unsigned long n;
 
-	n = (readl(base + pll->offset) >> 6) & 0x1ff;
+	val = readl(base + pll->offset);
+	n = FIELD_GET(STM32F4_RCC_PLLCFGR_N_MASK, val);
 
 	return parent_rate * n;
 }
@@ -673,9 +678,10 @@ static int stm32f4_pll_set_rate(struct clk_hw *hw, unsigned long rate,
 
 	n = rate  / parent_rate;
 
-	val = readl(base + pll->offset) & ~(0x1ff << 6);
+	val = readl(base + pll->offset) & ~STM32F4_RCC_PLLCFGR_N_MASK;
+	val |= FIELD_PREP(STM32F4_RCC_PLLCFGR_N_MASK, n);
 
-	writel(val | ((n & 0x1ff) <<  6), base + pll->offset);
+	writel(val, base + pll->offset);
 
 	if (pll_state)
 		stm32f4_pll_enable(hw);