linux nand flash驅(qū)動編寫
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，具體實現(xiàn)還要按照各個具體功能模塊來實現(xiàn)才行。
8、為什么我們都用s3c芯片進行舉例
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的版本進行分析的，大家可以直接查看這里的地址。
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