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linux nand flash驅(qū)動編寫

更新時間：2018年04月13日 08:40:09 作者：feixiaoxing

這篇文章主要介紹了linux nand flash驅(qū)動編寫，小編覺得挺不錯的，現(xiàn)在分享給大家，也給大家做個參考。一起跟隨小編過來看看吧

很長一段時間，nand flash都是嵌入式的標(biāo)配產(chǎn)品。nand flash價格便宜，存儲量大，適用于很多的場景?，F(xiàn)在很普及的ssd，上面的存儲模塊其實(shí)也是由一塊一塊nand flash構(gòu)成的。對于linux嵌入式來說，開始uboot的加載是硬件完成的，中期的kernel加載是由uboot中的nand flash驅(qū)動完成的，而后期的rootfs加載，這就要靠kernel自己來完成了。當(dāng)然，這次還是以三星s3c芯片為例進(jìn)行說明。

1、nand flash驅(qū)動在什么地方，可以從drviers/mtd/Makefile來看

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

2、nand在mtd下面，是作為一個單獨(dú)目錄保存的，這時應(yīng)該查看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" 
  depends 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、不難發(fā)現(xiàn)，MTD_NAND_S3C2410才是那個真正的macro，嘗試在Makefile找文件

obj-$(CONFIG_MTD_NAND_S3C2410)   += s3c2410.o

4、查看s3c2410.c文件，看看基本結(jié)構(gòu)構(gòu)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、繼續(xù)分析s3c24xx_nand_probe函數(shù)

s3c2410_nand_init_chip(info, nmtd, sets);

6、之所以從中摘出了s3c2410_nand_init_chip這個函數(shù)，是因為里面進(jìn)行了函數(shù)注冊

類似的函數(shù)還有s3c2410_nand_update_chip函數(shù)

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、抓住了函數(shù)接口，就找到了基本邏輯。

對于框架來說，它不關(guān)心你的代碼如何實(shí)現(xiàn)。只要你按照它的接口寫，就能讓上層正常獲得數(shù)據(jù)。platform、usb、pci這都是一種接口形式，具體實(shí)現(xiàn)還要按照各個具體功能模塊來實(shí)現(xiàn)才行。

8、為什么我們都用s3c芯片進(jìn)行舉例

因為它用的場景最多，學(xué)習(xí)資料最全，對于新手來說，這會少很多麻煩。

9、這個驅(qū)動依賴的kernel版本是什么

這里最有的代碼都是按照最新4.16的版本進(jìn)行分析的，大家可以直接查看這里的地址。

以上就是本文的全部內(nèi)容，希望對大家的學(xué)習(xí)有所幫助，也希望大家多多支持腳本之家。

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