STM32F4_RCC_PLLCFGR_N_MASK
n = FIELD_GET(STM32F4_RCC_PLLCFGR_N_MASK, val);
val = readl(base + pll->offset) & ~STM32F4_RCC_PLLCFGR_N_MASK;
val |= FIELD_PREP(STM32F4_RCC_PLLCFGR_N_MASK, n);
n = FIELD_GET(STM32F4_RCC_PLLCFGR_N_MASK, val);