linux nand flash驱动编写
<p>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。</p>
<p>
1、nand flash驱动在什么地方，可以从drviers/mtd/Makefile来看</p>
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<code class="plain plain">obj-y += chips/ lpddr/ maps/ devices/ nand/ onenand/ tests/</code>
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<p>
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</p>
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<code class="plain plain">config MTD_NAND_S3C2410 </code>
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<code class="plain spaces"> </code><code class="plain plain">tristate "NAND Flash support for Samsung S3C SoCs" </code>
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<code class="plain spaces"> </code><code class="plain plain">depends on ARCH_S3C24XX || ARCH_S3C64XX </code>
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<code class="plain spaces"> </code><code class="plain plain">help </code>
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<code class="plain spaces"> </code><code class="plain plain">This enables the NAND flash controller on the S3C24xx and S3C64xx </code>
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<code class="plain spaces"> </code><code class="plain plain">SoCs </code>
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<code class="plain spaces"> </code>
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<code class="plain spaces"> </code><code class="plain plain">No board specific support is done by this driver, each board </code>
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<code class="plain spaces"> </code><code class="plain plain">must advertise a platform_device for the driver to attach. </code>
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<code class="plain spaces"> </code>
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<code class="plain plain">config MTD_NAND_S3C2410_DEBUG </code>
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<code class="plain spaces"> </code><code class="plain plain">bool "Samsung S3C NAND driver debug" </code>
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<code class="plain spaces"> </code><code class="plain plain">depends on MTD_NAND_S3C2410 </code>
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<code class="plain spaces"> </code><code class="plain plain">help </code>
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<code class="plain spaces"> </code><code class="plain plain">Enable debugging of the S3C NAND driver </code>
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<code class="plain spaces"> </code>
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<code class="plain plain">config MTD_NAND_S3C2410_CLKSTOP </code>
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<code class="plain spaces"> </code><code class="plain plain">bool "Samsung S3C NAND IDLE clock stop" </code>
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<code class="plain spaces"> </code><code class="plain plain">depends on MTD_NAND_S3C2410 </code>
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<code class="plain spaces"> </code><code class="plain plain">default n </code>
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<code class="plain spaces"> </code><code class="plain plain">help </code>
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<code class="plain spaces"> </code><code class="plain plain">Stop the clock to the NAND controller when there is no chip </code>
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<code class="plain spaces"> </code><code class="plain plain">selected to save power. This will mean there is a small delay </code>
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<code class="plain spaces"> </code><code class="plain plain">when the is NAND chip selected or released, but will save </code>
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<code class="plain spaces"> </code><code class="plain plain">approximately 5mA of power when there is nothing happening.</code>
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<p>
3、不难发现，MTD_NAND_S3C2410才是那个真正的macro，尝试在Makefile找文件</p>
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<code class="plain plain">obj-$(CONFIG_MTD_NAND_S3C2410) += s3c2410.o</code>
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<p>
4、查看s3c2410.c文件，看看基本结构构成</p>
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<code class="cpp keyword bold">static</code> <code class="cpp keyword bold">struct</code> <code class="cpp plain">platform_driver s3c24xx_nand_driver = { </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.probe = s3c24xx_nand_probe, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.</code><code class="cpp functions bold">remove</code> <code class="cpp plain">= s3c24xx_nand_remove, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.suspend = s3c24xx_nand_suspend, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.resume = s3c24xx_nand_resume, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.id_table = s3c24xx_driver_ids, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.driver = { </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.name = </code><code class="cpp string">"s3c24xx-nand"</code><code class="cpp plain">, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.of_match_table = s3c24xx_nand_dt_ids, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">}, </code>
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<code class="cpp plain">}; </code>
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<code class="cpp spaces"> </code>
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<code class="cpp plain">module_platform_driver(s3c24xx_nand_driver);</code>
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<p>
5、继续分析s3c24xx_nand_probe函数</p>
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<code class="cpp plain">s3c2410_nand_init_chip(info, nmtd, sets);</code>
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<p>
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</p>
<p>
类似的函数还有s3c2410_nand_update_chip函数</p>
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<code class="cpp plain">chip->write_buf = s3c2410_nand_write_buf; </code>
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<code class="cpp plain">chip->read_buf = s3c2410_nand_read_buf; </code>
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<code class="cpp plain">chip->select_chip = s3c2410_nand_select_chip; </code>
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<code class="cpp plain">chip->chip_delay = 50; </code>
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<code class="cpp plain">nand_set_controller_data(chip, nmtd); </code>
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<code class="cpp plain">chip->options = set->options; </code>
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<code class="cpp plain">chip->controller = &info->controller; </code>
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<code class="cpp keyword bold">switch</code> <code class="cpp plain">(info->cpu_type) { </code>
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<code class="cpp keyword bold">case</code> <code class="cpp plain">TYPE_S3C2410: </code>
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<code class="cpp spaces"> </code><code class="cpp plain">chip->IO_ADDR_W = regs + S3C2410_NFDATA; </code>
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<code class="cpp spaces"> </code><code class="cpp plain">info->sel_reg = regs + S3C2410_NFCONF; </code>
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<code class="cpp spaces"> </code><code class="cpp plain">info->sel_bit = S3C2410_NFCONF_nFCE; </code>
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<code class="cpp spaces"> </code><code class="cpp plain">chip->cmd_ctrl = s3c2410_nand_hwcontrol; </code>
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<code class="cpp spaces"> </code><code class="cpp plain">chip->dev_ready = s3c2410_nand_devready; </code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">break</code><code class="cpp plain">; </code>
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<code class="cpp spaces"> </code>
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<code class="cpp keyword bold">case</code> <code class="cpp plain">TYPE_S3C2440: </code>
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<code class="cpp spaces"> </code><code class="cpp plain">chip->IO_ADDR_W = regs + S3C2440_NFDATA; </code>
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<code class="cpp spaces"> </code><code class="cpp plain">info->sel_reg = regs + S3C2440_NFCONT; </code>
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<code class="cpp spaces"> </code><code class="cpp plain">info->sel_bit = S3C2440_NFCONT_nFCE; </code>
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<code class="cpp spaces"> </code><code class="cpp plain">chip->cmd_ctrl = s3c2440_nand_hwcontrol; </code>
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<code class="cpp spaces"> </code><code class="cpp plain">chip->dev_ready = s3c2440_nand_devready; </code>
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<code class="cpp spaces"> </code><code class="cpp plain">chip->read_buf = s3c2440_nand_read_buf; </code>
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<code class="cpp spaces"> </code><code class="cpp plain">chip->write_buf = s3c2440_nand_write_buf; </code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">break</code><code class="cpp plain">; </code>
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<code class="cpp keyword bold">case</code> <code class="cpp plain">TYPE_S3C2412: </code>
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<code class="cpp spaces"> </code><code class="cpp plain">chip->IO_ADDR_W = regs + S3C2440_NFDATA; </code>
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<code class="cpp spaces"> </code><code class="cpp plain">info->sel_reg = regs + S3C2440_NFCONT; </code>
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<code class="cpp spaces"> </code><code class="cpp plain">info->sel_bit = S3C2412_NFCONT_nFCE0; </code>
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<code class="cpp spaces"> </code><code class="cpp plain">chip->cmd_ctrl = s3c2440_nand_hwcontrol; </code>
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<code class="cpp spaces"> </code><code class="cpp plain">chip->dev_ready = s3c2412_nand_devready; </code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">if</code> <code class="cpp plain">(readl(regs + S3C2410_NFCONF) & S3C2412_NFCONF_NANDBOOT) </code>
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<code class="cpp spaces"> </code><code class="cpp plain">dev_info(info->device, </code><code class="cpp string">"System booted from NAND\n"</code><code class="cpp plain">); </code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">break</code><code class="cpp plain">; </code>
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<code class="cpp plain">} </code>
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<p>
7、抓住了函数接口，就找到了基本逻辑。</p>
<p>
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。</p>
<p>
8、为什么我们都用s3c芯片进行举例</p>
<p>
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。</p>
<p>
9、这个驱动依赖的kernel版本是什么</p>
<p>
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。</p>
<p>
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。</p>
<p>
原文链接：https://blog.csdn.net/feixiaoxing/article/details/79855970</p>
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