devm_ioremap

devm_ioremap() is a function used in Linux kernel programming to map a physical memory region into the kernel's virtual address space. It is a variant of the ioremap() function that is designed to be used with managed devices in the kernel.

The devm prefix stands for device-managed, which means that the mapping is automatically released when the device is removed or the driver module is unloaded. This avoids the need for explicit cleanup code in the driver and reduces the risk of resource leaks.

The function takes three arguments: the device pointer, the physical address of the memory region to map, and the size of the region. It returns a virtual address that can be used to access the memory region from kernel code.

Here is an example usage of devm_ioremap():

static int my_driver_probe(struct platform_device *pdev)
{
    void __iomem *base_addr;
    int ret;

    base_addr = devm_ioremap(&pdev->dev, PHYS_ADDR, SIZE);
    if (!base_addr) {
        dev_err(&pdev->dev, "Failed to map memory region\n");
        return -ENOMEM;
    }

    // Use base_addr to access the memory region

    return 0;
}

In this example, the driver is using devm_ioremap() to map a physical memory region defined by the PHYS_ADDR and SIZE constants. If the mapping fails, an error message is printed and the probe function returns an error code. Otherwise, the driver can use the base_addr pointer to access the memory region.

When the device is removed or the driver module is unloaded, the memory mapping will be automatically released by the kernel.