devm_ioremap_resource

devm_ioremap_resource 是一个函数，它是 Linux 内核中的一部分，用于将设备的物理地址映射到内核虚拟地址空间。这个函数通常在设备驱动程序中使用，以便驱动程序可以访问设备的寄存器或内存区域。

函数的声明如下：

void __iomem *devm_ioremap_resource(struct device *dev, struct resource *res);

参数说明：

- `dev`：设备的 struct device 结构体指针。
- `res`：描述设备资源的 struct resource 结构体指针。

函数返回一个指向映射区域的指针，如果出错则返回 ERR_PTR()。

在函数内部，devm_ioremap_resource 首先调用 devm_request_mem_region 函数来请求设备内存区域，然后使用 ioremap_nocache 函数将物理地址映射到内核虚拟地址空间。最后，函数将 iounmap 函数注册到设备释放函数列表中，以确保设备被卸载时内存区域被正确释放。

请注意，devm_ioremap_resource 是 devm_ 函数族的一员，这意味着它使用了设备模型 (device model) 的内存管理机制，可以避免在驱动程序中手动释放内存区域。

相关问题

解析下面程序： mem = platform_get_resource(pdev, IORESOURCE_MEM, 0); chip->regs = devm_ioremap_resource(chip->dev, mem);

这段程序的作用是获取pdev设备的IORESOURCE_MEM资源，并将其映射到chip->regs变量上。其中，platform_get_resource用于获取pdev设备的资源，IORESOURCE_MEM表示资源类型为内存，0表示获取第一个IORESOURCE_MEM类型的资源。devm_ioremap_resource用于将资源映射到内存空间，并返回映射后的内存地址。

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.