linux nand flash驱动编写

很长一段时间，nand flash都是嵌入式的标配产品。nand flash价格便宜，存储量大，适用于很多的场景。现在很普及的ssd，上面的存储模块其实也是由一块一块nand flash构成的。对于linux嵌入式来说，开始uboot的加载是硬件完成的，中期的kernel加载是由uboot中的nand flash驱动完成的，而后期的rootfs加载，这就要靠kernel自己来完成了。当然，这次还是以三星s3c芯片为例进行说明。

1、nand flash驱动在什么地方，可以从drviers/mtd/Makefile来看

obj-y    += chips/ lpddr/ maps/ devices/ nand/ onenand/ tests/ 

2、nand在mtd下面，是作为一个单独目录保存的，这时应该查看nand下的Kconfig

config MTD_NAND_S3C2410 
  tristate "NAND Flash support for Samsung S3C SoCs" 
  depends on ARCH_S3C24XX || ARCH_S3C64XX 
  help 
   This enables the NAND flash controller on the S3C24xx and S3C64xx 
   SoCs 
 
   No board specific support is done by this driver, each board 
   must advertise a platform_device for the driver to attach. 
 
config MTD_NAND_S3C2410_DEBUG 
  bool "Samsung S3C NAND driver debug" 
  deaYZEUPlUpends on MTD_NAND_S3C2410 
  help 
   Enable debugging of the S3C NAND driver 
 
config MTD_NAND_S3C2410_CLKSTOP 
  bool "Samsung S3C NAND IDLE clock stop" 
  depends on MTD_NAND_S3C2410 
  default n 
  help 
   Stop the clock to the NAND controller when there is no chip 
   selected to save power. This will mean there is a small delay 
   when the is NAND chip selected or released, but will save 
   approximately 5mA of power when there is nothing happening. 

3、不难发现，MTD_NAND_S3C2410才是那个真正的macro，尝试在Makefile找文件

obj-$(CONFIG_MTD_NAND_S3C2410)   += s3c2410.o 

4、查看s3c2410.c文件，看看基本结构构成

static struct platform_driver s3c24xx_nand_driver = { 
  .probe   = s3c24xx_nand_probe, 
  .remove   = s3c24xx_nand_remove, 
  .suspend  = s3c24xx_nand_suspend, 
  .resume   = s3c24xx_nand_resume, 
  .id_table  = s3c24xx_driver_ids, 
  .driver   = { 
    .name  = "s3c24xx-nand", 
    .of_match_table = s3c24xx_nand_dt_ids, 
  }, 
}; 
 
module_platform_driver(s3c24xx_nand_driver); 

5、继续分析s3c24xx_nand_probe函数

s3c2410_nand_init_chip(info, nmtd, sets); 

6、之所以从中摘出了s3c2410_nand_init_chip这个函数，是因为里面进行了函数注册

类似的函数还有s3c2410_nand_update_chip函数

chip->write_buf  = s3c2410_nand_write_buf; 
chip->read_buf   = s3c2410_nand_read_buf; 
chip->select_chip = s3c2410_nand_select_chip; 
chip->chip_delay  = 50; 
nand_set_controller_data(chip, nmtd); 
chip->options    = set->options; 
chip->controller  = &info->controller;  
switch (info->cpu_type) { 
case TYPE_S3C2410: 
  chip->IO_ADDR_W = regs + S3C2410_NFDATA; 
  info->sel_reg  = regs + S3C2410_NFCONF; 
  info->sel_bit  = S3C2410_NFCONF_nFCE; 
  chip->cmd_ctrl = s3c2410_nand_hwcontrol; 
  chip->dev_ready = s3c2410_nand_devready; 
  break; 
 
case TYPE_S3C2440: 
  chip->IO_ADDR_W = regs + S3C2440_NFDATA; 
  info->sel_reg  = regs + S3C2440_NFCONT; 
  info->sel_bit  = S3C2440_NFCONT_nFCE; 
  chip->cmd_ctrl = s3c2440_nand_hwcontrol; 
  chip->dev_ready = s3c2440_nand_devready; 
  chip->read_buf = s3c2440_nand_read_buf; 
  chip->write_buf = s3c2440_nand_write_buf; 
  break;  
case TYPE_S3C2412: 
  chip->IO_ADDR_W = regs + S3C2440_NFDATA; 
  info->sel_reg  = regs + S3C2440_NFCONT; 
  info->sel_bit  = S3C2412_NFCONT_nFCE0; 
  chip->cmd_ctrl = s3c2440_nand_hwcontrol; 
  chip->dev_ready = s3c2412_nand_devready;  
  if (readl(regs + S3C2410_NFCONF) & S3C2412_NFCONF_NANDBOOT) 
    dev_info(info->device, "System booted from NAND\n");  
  break; 
} 

7、抓住了函数接口，就找到了基本逻辑。

对于框架来说，它不关心你的代码如何实现。只要你按照它的接口写，就能让上层正常获得数据。platform、usb、pci这都是一种接口形式，具体实现还要按照各个具体功能模块来实现才行。

8、为什么我们都用s3c芯片进行举例

因为它用的场景最多，学习资料最全，对于新手来说，这会少很多麻烦。

9、这个驱动依赖的kernel版本是什么

这里最有的代码都是按照最新4.16的版本进行分析的，大家可以直接查看这里的地址。

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