如何为 sysfs 属性创建大量类似的函数？

Question

我的 FPGA 中有一个通用 AXI 从设备，带有多个 I/O 寄存器。我想使用 sysfs 接口访问我的寄存器。对于我想要访问的每个寄存器，我创建一个_show和 一个_store函数，但这会需要很多代码。

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);

例如，当创建 32 个寄存器时，我必须执行 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，特别是对于给定的 sysfs-attribute 用例？

Answer 1

您的_show和_store函数不使用struct device_attribute *attr参数，但确切地说此参数旨在包含有关给定文件表示的特定事物的信息：

// 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);

类似的方法也用在DEVICE_ULONG_ATTR宏中，定义在include/linux/device.h中。该宏为“long”类型的变量创建一个属性。