很長(zhǎng)一段時(shí)間，nand flash都是嵌入式的標(biāo)配產(chǎn)品。nand flash價(jià)格便宜，存儲(chǔ)量大，適用于很多的場(chǎng)景?，F(xiàn)在很普及的ssd，上面的存儲(chǔ)模塊其實(shí)也是由一塊一塊nand flash構(gòu)成的。對(duì)于linux嵌入式來(lái)說(shuō)，開(kāi)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(dòng)完成的，而后期的rootfs加載，這就要靠kernel自己來(lái)完成了。當(dāng)然，這次還是以三星s3c芯片為例進(jìn)行說(shuō)明。
1、nand flash驅(qū)動(dòng)在什么地方，可以從drviers/mtd/Makefile來(lái)看
obj-y += chips/ lpddr/ maps/ devices/ nand/ onenand/ tests/
2、nand在mtd下面，是作為一個(gè)單獨(dú)目錄保存的，這時(shí)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(gè)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(gè)函數(shù)，是因?yàn)槔锩孢M(jìn)行了函數(shù)注冊(cè)
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(duì)于框架來(lái)說(shuō)，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(xiě)，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(gè)具體功能模塊來(lái)實(shí)現(xiàn)才行。
8、為什么我們都用s3c芯片進(jìn)行舉例
因?yàn)樗玫膱?chǎng)景最多，學(xué)習(xí)資料最全，對(duì)于新手來(lái)說(shuō)，這會(huì)少很多麻煩。
9、這個(gè)驅(qū)動(dòng)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?jī)?nèi)容，希望對(duì)大家的學(xué)習(xí)有所幫助，也希望大家多多支持VEVB武林網(wǎng)。
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