read only zero from ioremap register on STM32MP157

Question

I want to access an register , it's phy address is 0x50002000, in the driver init function, I can read out the value:

    gpioa = ioremap(0x50002000, 4);

    
    printk("ioremap(0x50002000) = 0x%x\n", gpioa);

    for (i = 0; i < 10; i++)
        printk("gpioa_mode = 0x%x\n", *gpioa);

But in the read function of file_operations, the value is always zero:

static ssize_t led_drv_read (struct file *file, char __user *buf, size_t size, loff_t *offset)
{
    printk("gpioa_mode(0x%x) = 0x%x\n", gpioa, ioread32(gpioa));
    return 0;
}

With devmem, it is zero too:

# devmem 0x50002000 32
0x00000000

Why ? Thank you.

I want to use ioremap to debug my driver, but it can not work.