问题现象：
[ 2.120000] VFS: Cannot open root device "mtdblock5" or unknown-block(0,0): error -6
[ 2.136000] Please append a correct "root=" boot option; here are the available partitions:
[ 2.152000] 1f00 4096 mtdblock0 (driver?)
[ 2.164000] 1f01 192 mtdblock1 (driver?)
[ 2.172000] 1f02 64 mtdblock2 (driver?)
[ 2.184000] 1f03 64 mtdblock3 (driver?)
[ 2.192000] 1f04 3776 mtdblock4 (driver?)
[ 2.204000] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
导致该问题的原因：flash分区不对
第一种情况是根本没有做分区，没有出现下面的启动信息
[ 0.460000] Creating 4 MTD partitions on "spi32766.0":
[ 0.470000] 0x000000000000-0x000000030000 : "u-boot"
[ 0.480000] 0x000000030000-0x000000040000 : "u-boot-env"
[ 0.490000] 0x000000040000-0x000000050000 : "factory"
[ 0.500000] 0x000000050000-0x000000400000 : "firmware"
像MTK的就需要在dts文件中添加flash分区
target/linux/ramips/dts/MT7621.dts
palmbus@1E000000 {
spi@b00 {
status = "okay";
m25p80@0 {
#address-cells = <1>;
#size-cells = <1>;
compatible = "w25q128";
reg = <0 0>;
linux,modalias = "m25p80";
spi-max-frequency = <10000000>;
partition@0 {
label = "u-boot";
reg = <0x0 0x30000>;
read-only;
};
partition@30000 {
label = "u-boot-env";
reg = <0x30000 0x10000>;
read-only;
};
factory: partition@40000 {
label = "factory";
reg = <0x40000 0x10000>;
read-only;
};
partition@50000 {
label = "firmware";
reg = <0x50000 0xfb0000>;
};
};
};
第二种情况是dts文件中添加了flash分区，flash大小没配置正常
label = "firmware";
reg = <0x50000 0xfb0000>; // 16M = 0x50000 + 0xfb0000
要是板子是4M的，4M = 0x50000 + 0x3b0000，需要调整为reg = <0x50000 0x3b0000>;
第三种情况是分区没有分完整，rootfs分区没出来
[ 0.460000] Creating 4 MTD partitions on "spi32766.0":
[ 0.470000] 0x000000000000-0x000000030000 : "u-boot"
[ 0.480000] 0x000000030000-0x000000040000 : "u-boot-env"
[ 0.490000] 0x000000040000-0x000000050000 : "factory"
[ 0.500000] 0x000000050000-0x000000400000 : "firmware"
在uboot启动阶段有以下打印
## Booting image at bc030000 ...
此种情况下"firmware"的分区起始地址要放在0x000000030000，即 0x000000030000-0x000000400000 : "firmware"
或者
## Booting image at bc050000 ...
此种情况下"firmware"的分区起始地址要放在0x000000050000，即 0x000000050000-0x000000400000 : "firmware"
配置正确后可出现如下分区信息：
[ 1.608000] 2 uimage-fw partitions found on MTD device firmware
[ 1.620000] 0x000000030000-0x000000165801 : "kernel"
[ 1.632000] mtd: partition "kernel" must either start or end on erase block boundary or be smaller than an erase block -- forcing read-only
[ 1.656000] 0x000000165801-0x000000400000 : "rootfs"
[ 1.668000] mtd: partition "rootfs" must either start or end on erase block boundary or be smaller than an erase block -- forcing read-only
[ 1.696000] 1 squashfs-split partitions found on MTD device rootfs
[ 1.708000] 0x000000330000-0x000000400000 : "rootfs_data"
最后，要出现以上分割firmware分区的效果，需要配置kernel
执行make kernel_menuconfig
MTK openwrt 3.10.14的SDK，有的flash分区不在dts文件中,需要在源码中调整，譬如以下
vi build_dir/target-mipsel_24kec+dsp_uClibc-0.9.33.2/linux-ramips_mt7628/linux-3.10.14-p112871/drivers/mtd/ralink/ralink_bbu_spi.c
