CLK_DIV_FACTOR_APB_CLK
writel(0x4, isys_base + IS_IO_GPREGS_BASE + CLK_DIV_FACTOR_APB_CLK);
writel(0x2, isys_base + offset + CLK_DIV_FACTOR_APB_CLK);
readl(isys_base + offset + CLK_DIV_FACTOR_APB_CLK));