Use ioremap(cookie, size) to create a driver
The ioremap macro is defined in asm/io.h
eg:IMX6U_CCM_CCGR1 = ioremap(CCM_CCGR1_BASE, 4);
Use iounmap to unregister the driver
2. Analysis of ioremap() related functions
After mapping the physical address of the I/O memory resource to the core virtual address, theoretically speaking, we can directly read and write the I/O memory resource like reading and writing RAM. In order to ensure the cross-platform portability of the driver, we should use specific functions in Linux to access I/O memory resources instead of using pointers to core virtual addresses .
The functions for reading and writing I/O are as follows:
a -- writel()
writel() writes data to the memory-mapped I/O space , and wirtel() writes 32-bit data (4 bytes) to I/O.
原型：void writel (unsigned char data , unsigned int addr )
b -- readl()
readl() reads data from memory-mapped I/O space , and readl reads 32-bit data (4 bytes) from I/O.
Prototype: unsigned char readl (unsigned int addr)
eg:
/* 2. Enable GPIO1 clock*/
val = readl(IMX6U_CCM_CCGR1);
val &= ~(3 << 26); /* Clear the previous setting*/
val |= (3 << 26); /* Set the new value */
writel(val, IMX6U_CCM_CCGR1);
readl() and writel() can cooperate with each other to realize the flashing of led, etc.
void led_switch(u8 sta)
{ u32 val = 0; if(sta == LEDON) { val = readl(GPIO1_DR);//Read the value of GPIO1_DR register val &= ~(1 << 3); //Register For the value, the value of shifting 1 to the left by 3 bits is reversed, then ANDed with val, and then assigned to val write(val, GPIO1_DR);//write val to the GPIO1_DR register } else if(sta == LEDOFF) { val = readl (GPIO1_DR); val|= (1 << 3); write(val, GPIO1_DR); } }