带cache的nand flash驱动怎么写

下面是一个简单的带cache的nand flash驱动的示例代码：

#include <linux/mtd/mtd.h>
#include <linux/mtd/nand.h>

#define CACHE_SIZE 4096

struct nand_cache {
    u8 data[CACHE_SIZE];
    int page;
    bool dirty;
};

struct my_nand {
    struct nand_chip chip;
    struct nand_cache cache;
};

static int my_nand_read_page(struct mtd_info *mtd, struct nand_chip *chip,
                    uint32_t page, uint8_t *buf, int len)
{
    struct my_nand *my_chip = container_of(chip, struct my_nand, chip);

    if (my_chip->cache.page == page) {
        memcpy(buf, my_chip->cache.data, len);
    } else {
        int ret = nand_read_page(mtd, chip, page, buf, len);
        if (ret == 0) {
            my_chip->cache.page = page;
            memcpy(my_chip->cache.data, buf, len);
        }
        return ret;
    }
}

static int my_nand_write_page(struct mtd_info *mtd, struct nand_chip *chip,
                     uint32_t page, uint8_t *buf, int len)
{
    struct my_nand *my_chip = container_of(chip, struct my_nand, chip);

    int ret = nand_write_page(mtd, chip, page, buf, len);
    if (ret == 0) {
        my_chip->cache.page = page;
        memcpy(my_chip->cache.data, buf, len);
        my_chip->cache.dirty = true;
    }
    return ret;
}

static int my_nand_erase(struct mtd_info *mtd, struct erase_info *instr)
{
    struct my_nand *my_chip = container_of(mtd_to_nand(mtd), struct my_nand, chip);

    int ret = nand_erase(mtd, instr);
    if (ret == 0) {
        my_chip->cache.page = -1;
        my_chip->cache.dirty = false;
    }
    return ret;
}

static struct my_nand my_nand_chip = {
    .chip = {
        .read_page = my_nand_read_page,
        .write_page = my_nand_write_page,
        .erase = my_nand_erase,
        // ...other nand_chip functions
    },
    .cache = {
        .page = -1,
        .dirty = false,
    },
};

static int my_nand_probe(struct platform_device *pdev)
{
    int ret;

    // Initialize the nand_chip structure
    my_nand_chip.chip.dev.parent = &pdev->dev;
    my_nand_chip.chip.IO_ADDR_R = /* NAND read address */;
    my_nand_chip.chip.IO_ADDR_W = /* NAND write address */;
    // ...other nand_chip initialization

    // Register the NAND flash with the MTD subsystem
    ret = nand_scan(&my_nand_chip.chip, /* number of chip enables */, NULL);
    if (ret != 0) {
        return ret;
    }

    // Register the MTD device
    ret = mtd_device_register(&my_nand_chip.chip, /* partition info */, /* number of partitions */, NULL);
    if (ret != 0) {
        nand_release(&my_nand_chip.chip);
        return ret;
    }

    return 0;
}

static int my_nand_remove(struct platform_device *pdev)
{
    mtd_device_unregister(&my_nand_chip.chip);
    nand_release(&my_nand_chip.chip);
    return 0;
}

static struct platform_driver my_nand_driver = {
    .probe = my_nand_probe,
    .remove = my_nand_remove,
    .driver = {
        .name = "my_nand",
        // ...other driver information
    },
};

module_platform_driver(my_nand_driver);

上面的代码中，`my_nand_read_page`和`my_nand_write_page`函数会先检查缓存中是否有该页的数据，如果有就直接从缓存中读取或将数据写入缓存。如果缓存中没有该页的数据，则调用原始的`nand_read_page`或`nand_write_page`函数读取或写入NAND flash，并更新缓存。`my_nand_erase`函数会在NAND flash擦除时清除缓存。在`my_nand_chip`结构体中，我们通过`cache`成员变量来保存缓存的数据和状态。在`my_nand_probe`函数中，我们先初始化`my_nand_chip`结构体的`chip`成员，然后调用`nand_scan`函数注册NAND flash，并调用`mtd_device_register`函数注册MTD设备。在`my_nand_remove`函数中，我们需要注销MTD设备和NAND flash。最后，我们使用`module_platform_driver`宏来注册驱动程序。