drivers/mfd/Mfd-core.c

mfd: multifunction device drivers---多功能设备驱动开发；
A product or device that has multiple functions. An example of this might be a printer that also makes copies, faxes, and scans. Another example is a CD or DVD that might contain multiple applications on the same disk; this may be a Mac and PC version of the same software or media meant to be played on more than one platform. Also called multi function product (MFP), all-in-one.

源码主要是做了一些platform_device的注册和添加删除工作。

int mfd_add_devices(struct device *parent, int id,
            struct mfd_cell *cells, int n_devs,
            struct resource *mem_base,
            int irq_base)
{
    int i;
    int ret = 0;
    atomic_t *cnts;

    /* initialize reference counting for all cells */
    cnts = kcalloc(n_devs, sizeof(*cnts), GFP_KERNEL);
    if (!cnts)
        return -ENOMEM;

    for (i = 0; i < n_devs; i++) {
        atomic_set(&cnts[i], 0);
        cells[i].usage_count = &cnts[i];
        ret = mfd_add_device(parent, id, cells + i, mem_base, irq_base); 调用mfd_add_device()
        if (ret)
            break;
    }

    if (ret)
        mfd_remove_devices(parent);

    return ret;
}
EXPORT_SYMBOL(mfd_add_devices);

在这个函数中，参数cells是数组，个数为参数n_devs。用户调用此函数前初始化了cells部分内容，但其中成员由本函数初始化：

/*
 * This struct describes the MFD part ("cell").
 * After registration the copy of this structure will become the platform data
 * of the resulting platform_device
 */
struct mfd_cell {  //个人理解：注册mfd_cell后等效为platform_device
    const char      *name;
    int         id;

    /* refcounting for multiple drivers to use a single cell */
    atomic_t        *usage_count;　　　　//本函数初始化
    int         (*enable)(struct platform_device *dev);
    int         (*disable)(struct platform_device *dev);

    int         (*suspend)(struct platform_device *dev);
    int         (*resume)(struct platform_device *dev);

    /* platform data passed to the sub devices drivers */
    void            *platform_data;
    size_t          pdata_size;

    /*
     * These resources can be specified relative to the parent device.
     * For accessing hardware you should use resources from the platform dev
     */
    int         num_resources;
    const struct resource   *resources;

    /* don't check for resource conflicts */
    bool            ignore_resource_conflicts;

    /*
     * Disable runtime PM callbacks for this subdevice - see
     * pm_runtime_no_callbacks().
     */
    bool            pm_runtime_no_callbacks;
};

再来看mfd_add_device()

static int mfd_add_device(struct device *parent, int id,
              const struct mfd_cell *cell,
              struct resource *mem_base,
              int irq_base)
{
    struct resource *res;
    struct platform_device *pdev;
    int ret = -ENOMEM;
    int r;

    pdev = platform_device_alloc(cell->name, id + cell->id); //申请pdev内存并初始化name和id
    if (!pdev)
        goto fail_alloc;

    res = kzalloc(sizeof(*res) * cell->num_resources, GFP_KERNEL);
    if (!res)
        goto fail_device;

    pdev->dev.parent = parent;
    pdev->dev.type = &mfd_dev_type;

    if (cell->pdata_size) {  //重新分配pdev->dev. platform_data内存并将cell->platform_data赋给它。
        ret = platform_device_add_data(pdev,
                    cell->platform_data, cell->pdata_size);
        if (ret)
            goto fail_res;
    }

    ret = mfd_platform_add_cell(pdev, cell); //重新分配pdev->mfd_cell内存并将cell赋给它。
    if (ret)
        goto fail_res;

//初始化cell->num_resources 个数量的res将它赋给pdev->resource
    for (r = 0; r < cell->num_resources; r++) {
        res[r].name = cell->resources[r].name;
        res[r].flags = cell->resources[r].flags;

        /* Find out base to use */
        if ((cell->resources[r].flags & IORESOURCE_MEM) && mem_base) {
            res[r].parent = mem_base;
            res[r].start = mem_base->start +    //cell中的每个内存start都要加上mem_base->start
                cell->resources[r].start;
            res[r].end = mem_base->start +
                cell->resources[r].end;
        } else if (cell->resources[r].flags & IORESOURCE_IRQ) {
            res[r].start = irq_base +           //每个cell中的irq都要加上irq_base。
                cell->resources[r].start;
            res[r].end   = irq_base +
                cell->resources[r].end;
        } else {
            res[r].parent = cell->resources[r].parent;
            res[r].start = cell->resources[r].start;
            res[r].end   = cell->resources[r].end;
        }

        if (!cell->ignore_resource_conflicts) {
            ret = acpi_check_resource_conflict(&res[r]);
            if (ret)
                goto fail_res;
        }
    }

    ret = platform_device_add_resources(pdev, res, cell->num_resources);//将多个res赋给pdev
    if (ret)
        goto fail_res;

    ret = platform_device_add(pdev); //添加一个platform_device到系统，这时在dev的驱动中会使用这些res数据。
    if (ret)
        goto fail_res;

    if (cell->pm_runtime_no_callbacks)
        pm_runtime_no_callbacks(&pdev->dev);

    kfree(res);

    return 0;

fail_res:
    kfree(res);
fail_device:
    platform_device_put(pdev);
fail_alloc:
    return ret;
}