am335x how to set gpio in linux kernel

Hi dear

i'm using {"mcasp0_ahclkx.gpio3_21",        OMAP_MUX_MODE7 | AM33XX_PIN_OUTPUT},to turn on my LCD.i want to set gpio3_21 to high in kernel. i find the function

void omap_mux_write(struct omap_mux_partition *partition, u16 val,
               u16 reg)
{
    if (partition->flags & OMAP_MUX_REG_8BIT)
        __raw_writeb(val, partition->base + reg);
    else
        __raw_writew(val, partition->base + reg);
},

i printk the value when list the pin ,below is the value

[    0.976165] muxmode=7
[    0.978546] partitionname=core
[    0.981781] partitionflag=0
[    0.984741] partitionbase=f9e10000(a pointer address)
[    0.988311] muxregoffset=2476(0x9ac)

i read the AM335x ARM® CortexTM-A8 Microprocessors(MPUs) Technical Reference Manual, gpio3 address is 0x481A_E000 - 0x481A_EFFF, the GPIO_DATAOUT Register (offset = 13Ch) , the address confused me. how can i to set the gpio3_21 to high in linux kernel?