c - 如何为 sysfs 属性创建许多类似的函数？

Question

我的 FPGA 中有一个带有多个 I/O 寄存器的通用 AXI 从设备。我想使用 sysfs 接口(interface)访问我的寄存器。对于我想要访问的每个寄存器，我都创建了一个 _show 和一个 _store 函数，但这将需要很多代码。

static ssize_t writereg0_store(struct device *dev, struct device_attribute                *attr, const char *buf, size_t count) {
    struct axi_register_driver *drv = dev_get_drvdata(dev);
    u32 val;

    if (kstrtou32(buf, 10, &val) != 0)
        return -EINVAL;

    iowrite32(val, drv->reg_base + WRITE_OFFSET + 0);

    return count;

}

static ssize_t writereg0_show(struct device *dev, struct device_attribute *attr, char *buf) {
    struct axi_register_driver *drv = dev_get_drvdata(dev);

    u32 reg;
    reg = ioread32(drv->reg_base + WRITE_OFFSET + 0);

    return sprintf(buf, "0x%x\n", reg);
}
static DEVICE_ATTR_RW(writereg0);

static ssize_t readreg0_show(struct device *dev, struct device_attribute *attr, char *buf) {
    struct axi_register_driver *drv = dev_get_drvdata(dev);

    u32 reg;
    reg = ioread32(drv->reg_base + 0);

    return sprintf(buf, "0x%x\n", reg);
}
static DEVICE_ATTR_RO(readreg0);

第二个只读寄存器基本相同，只是函数名和地址偏移量不同:

static ssize_t readreg1_show(struct device *dev, struct device_attribute *attr, char *buf) {
    struct axi_register_driver *drv = dev_get_drvdata(dev);

    u32 reg;
    reg = ioread32(drv->reg_base + OFF_REG1);

    return sprintf(buf, "0x%x\n", reg);
}
static DEVICE_ATTR_RO(readreg1);

当创建例如32 个寄存器，我必须这样做 32 次；代码不会很漂亮。

那么创建一堆类似函数的最佳方法是什么，尤其是对于给定的 sysfs-attribute 用例？

Answer 1

您的_show 和_store 函数不使用struct device_attribute *attr 参数，但恰恰该参数用于包含特定信息由给定文件表示的事物:

// Derive 'device_attribute' structure for a read register's attribute
struct dev_axi_read_reg_attribute {
    struct device_attribute attr;
    int reg_offset; // Offset of the register here
};

// Generic 'show' method, suitable for every read register
static ssize_t read_axi_reg_show(struct device *dev, struct device_attribute *attr, char *buf) {
    struct axi_register_driver *drv = dev_get_drvdata(dev);
    // 'attr' is actually of type `struct dev_axi_read_reg_attribute`.
    // See definition of the macro 'AXI_READ_REG_ATTR' below.
    struct dev_axi_read_reg_attribute* axi_read_attr = container_of(attr,
        struct dev_axi_read_reg_attribute, attr);

    u32 reg;
    // Take offset to the register from the attribute
    reg = ioread32(drv->reg_base + axi_read_attr->reg_offset);

    return sprintf(buf, "0x%x\n", reg);
}

// Macro for declare attribute for read register
#define AXI_READ_REG_ATTR(_name, _reg_offset) \
struct dev_axi_read_reg_attribute dev_attr_##_name = \
    { __ATTR(_name,  S_IRUGO, read_axi_reg_show, NULL), _reg_offset }

// Declare as many attributes as you want
static AXI_READ_REG_ATTR(readreg0, OFF_REG0);
static AXI_READ_REG_ATTR(readreg1, OFF_REG1);
// ...

static struct attribute *axi_register_attrs[] = {
    &dev_attr_readreg0.attr.attr,
    &dev_attr_readreg1.attr.attr,
    // ...
    NULL,
};
ATTRIBUTE_GROUPS(axi_register);

在 DEVICE_ULONG_ATTR 宏中使用了类似的方法，在 include/linux/device.h 中定义.该宏为“long”类型的变量创建了一个属性。