在Linux运行期间升级Linux系统（Uboot+kernel+Rootfs）

1.1.1. Linux中已经实现Nor Flash驱动

在spi接口的nor flash设备注册部分搞定后，再来看Linux中的，默认已经帮我们实现好了的一个通用的nor flash的驱动。

具体的文件是：

linux-2.6.28.4\drivers\mtd\devices\m25p80.c

其中，对于支持的设备，可以去看源码中的设备列表部分的代码：

/* NOTE: double check command sets and memory organization when you add
 * more flash chips.  This current list focusses on newer chips, which
 * have been converging on command sets which including JEDEC ID.
 */
static struct flash_info __devinitdata m25p_data [] = {

	/* Atmel -- some are (confusingly) marketed as "DataFlash" */
	{ "at25fs010",  0x1f6601, 0, 32 * 1024, 4, SECT_4K, },
	{ "at25fs040",  0x1f6604, 0, 64 * 1024, 8, SECT_4K, },

	{ "at25df041a", 0x1f4401, 0, 64 * 1024, 8, SECT_4K, },
	{ "at25df641",  0x1f4800, 0, 64 * 1024, 128, SECT_4K, },

	{ "at26f004",   0x1f0400, 0, 64 * 1024, 8, SECT_4K, },
	{ "at26df081a", 0x1f4501, 0, 64 * 1024, 16, SECT_4K, },
	{ "at26df161a", 0x1f4601, 0, 64 * 1024, 32, SECT_4K, },
	{ "at26df321",  0x1f4701, 0, 64 * 1024, 64, SECT_4K, },

	/* Spansion -- single (large) sector size only, at least
	 * for the chips listed here (without boot sectors).
	 */
	{ "s25sl004a", 0x010212, 0, 64 * 1024, 8, },
	{ "s25sl008a", 0x010213, 0, 64 * 1024, 16, },
	{ "s25sl016a", 0x010214, 0, 64 * 1024, 32, },
	{ "s25sl032a", 0x010215, 0, 64 * 1024, 64, },
	{ "s25sl064a", 0x010216, 0, 64 * 1024, 128, },
        { "s25sl12800", 0x012018, 0x0300, 256 * 1024, 64, },
	{ "s25sl12801", 0x012018, 0x0301, 64 * 1024, 256, },

	/* SST -- large erase sizes are "overlays", "sectors" are 4K */
	{ "sst25vf040b", 0xbf258d, 0, 64 * 1024, 8, SECT_4K, },
	{ "sst25vf080b", 0xbf258e, 0, 64 * 1024, 16, SECT_4K, },
	{ "sst25vf016b", 0xbf2541, 0, 64 * 1024, 32, SECT_4K, },
	{ "sst25vf032b", 0xbf254a, 0, 64 * 1024, 64, SECT_4K, },

	/* ST Microelectronics -- newer production may have feature updates */
	{ "m25p05",  0x202010,  0, 32 * 1024, 2, },
	{ "m25p10",  0x202011,  0, 32 * 1024, 4, },
	{ "m25p20",  0x202012,  0, 64 * 1024, 4, },
	{ "m25p40",  0x202013,  0, 64 * 1024, 8, },
	{ "m25p80",         0,  0, 64 * 1024, 16, },
	{ "m25p16",  0x202015,  0, 64 * 1024, 32, },
	{ "m25p32",  0x202016,  0, 64 * 1024, 64, },
	{ "m25p64",  0x202017,  0, 64 * 1024, 128, },
	{ "m25p128", 0x202018, 0, 256 * 1024, 64, },

	{ "m45pe80", 0x204014,  0, 64 * 1024, 16, },
	{ "m45pe16", 0x204015,  0, 64 * 1024, 32, },

	{ "m25pe80", 0x208014,  0, 64 * 1024, 16, },
	{ "m25pe16", 0x208015,  0, 64 * 1024, 32, SECT_4K, },

	/* Winbond -- w25x "blocks" are 64K, "sectors" are 4KiB */
	{ "w25x10", 0xef3011, 0, 64 * 1024, 2, SECT_4K, },
	{ "w25x20", 0xef3012, 0, 64 * 1024, 4, SECT_4K, },
	{ "w25x40", 0xef3013, 0, 64 * 1024, 8, SECT_4K, },
	{ "w25x80", 0xef3014, 0, 64 * 1024, 16, SECT_4K, },
	{ "w25x16", 0xef3015, 0, 64 * 1024, 32, SECT_4K, },
	{ "w25x32", 0xef3016, 0, 64 * 1024, 64, SECT_4K, },
	{ "w25x64", 0xef3017, 0, 64 * 1024, 128, SECT_4K, },
};
            

如果要添加此驱动，以实现支持我们的通用的nor flash，则在make menuconfig的时候，添加对应设备的支持即可。

对应选项的kconfig的配置内容在：

linux-2.6.28.4\drivers\mtd\devices\kconfig

中：

config MTD_M25P80
	tristate "Support most SPI Flash chips (AT26DF, M25P, W25X, ...)"
	depends on SPI_MASTER && EXPERIMENTAL
	help
	  This enables access to most modern SPI flash chips, used for
	  program and data storage.   Series supported include Atmel AT26DF,
	  Spansion S25SL, SST 25VF, ST M25P, and Winbond W25X.  Other chips
	  are supported as well.  See the driver source for the current list,
	  or to add other chips.

	  Note that the original DataFlash chips (AT45 series, not AT26DF),
	  need an entirely different driver.

	  Set up your spi devices with the right board-specific platform data,
	  if you want to specify device partitioning or to use a device which
	  doesn't support the JEDEC ID instruction.
            

如上所述，如果这些步骤都做完了，最后新编译生成的linux内核，运行后，就应该可以可以通过：

cat /proc/mtd

查看到对应的mtd设备了。如果没有，那么说明你的驱动还是没有添加正常。