在做之前参考了如下博客文章，再次非常感谢：
http://www.cnblogs.com/pengdonglin137/p/6241895.html
Uboot中需要在config中添加如下宏：
#define CONFIG_FIT 1
在内核里面make menuconfig之后配置支持设备树：
Boot options->
[*] Flattened Device Tree support
然后分别编译uboot和kernel，最后按照网上介绍制作dtb文件，将uboot通过jlink直接烧到nor flash的0地址处，然后用tftp将kernel下载到内存的30000000,将dtb文件烧到内存的31000000,然后用bootm 30000000 - 31000000启动系统，但只能看到：
SMDK2440 # bootm -
## Booting kernel from Legacy Image at ...
Image Name: Linux-4.15.-gc1aaab686-dirty
Image Type: ARM Linux Kernel Image (uncompressed)
Data Size: Bytes = 3.3 MiB
Load Address:
Entry Point:
Verifying Checksum ... OK
## Flattened Device Tree blob at
Booting using the fdt blob at 0x31000000
Loading Kernel Image ... OK
Loading Device Tree to 33ba6000, end 33baa6ea ... OK Starting kernel ...
因为之前使用tags内核能正确启动，所以目前就是怀疑dtb文件没有正确传到linux，但是在uboot的/include/common.h里面添加#define DEBUG将uboot的所以调试信息打开，能看到dtb文件已经被uboot识别并且拷贝到内存的另一个地方了，如果按下开发板上的reset按键再一次进到uboot的console，在用dm.w去看dtb，能正确的看到dtb的内容，所以目前怀疑2点：
1.设备树不被kernel识别。
2.设备树被正确识别，但bootargs没有被正确读取，到处串口没有正确配置。
解决问题：
1.刚开始无法定位在linux kernel哪里挂掉的，于是添加了led灯，在没有开启MMU之前，可以直接操作物理地址，一直查到：
ENTRY(__turn_mmu_on)
mov r0, r0
instr_sync
mcr p15, , r0, c1, c0, @ write control reg
mrc p15, , r3, c0, c0, @ read id reg
instr_sync
mov r3, r3
mov r3, r13
ret r3
这里的MMU被打开了，就不能直接操作物理地址了，再往后执行就是调用__mmap_switched，因为很早就有ldr r13, =__mmap_switched @ address to jump to after，然后在__mmap_switched的最后就是执行C代码入口b start_kernel。
于是断定肯定执行到了c阶段，但此时MMU已经开启，不清楚如何调试，于是又想到了earlyprintk，不爽的就是earlyprintk需要添加到bootargs里面，因为kernel C代码里面回去解析，暂时还没分析为什么非要uboot传过来。
我现在的问题就很有可能uboot的bootargs没有正确传过来，本来想动脑筋在代码里面写死bootargs里面有earlyprintk的，后来突然想到make menuconfig有一个默认的Default kernel command string，于是我配置如下：
再次编译内核，烧到板子上运行，终于有进步了：
SMDK2440 # bootm -
## Booting kernel from Legacy Image at ...
Image Name: Linux-4.15.-gc1aaab686-dirty
Image Type: ARM Linux Kernel Image (uncompressed)
Data Size: Bytes = 3.3 MiB
Load Address:
Entry Point:
Verifying Checksum ... OK
## Flattened Device Tree blob at
Booting using the fdt blob at 0x31000000
Loading Kernel Image ... OK
Loading Device Tree to 33ba6000, end 33baa6ea ... OK Starting kernel ... Uncompressing Linux... done, booting the kernel. 我在misc.c里面添加了写打印信息，如下：
static void puthex(const int dat)
{
char c;
unsigned char temp[4]={0}; temp[0] = dat/1000 + 0x30;
temp[1] = dat%1000/100 + 0x30;
temp[2] = dat%100/10 + 0x30;
temp[3] = dat%10 + 0x30;
putc(temp[0]);
putc(temp[1]);
putc(temp[2]);
putc(temp[3]);
putc('\r');
putc('\n');
flush();
} void DispDeviceTree(int arch_id,unsigned long* dev_tree)
{
char temp_str[100]; sprintf(temp_str,"machid=%d",arch_id);
putstr(temp_str);
sprintf(temp_str,"devTree=%s",dev_tree);
putstr(temp_str);
}
然后在head.s里面添加了加上这个函数
/*
* The C runtime environment should now be setup sufficiently.
* Set up some pointers, and start decompressing.
* r4 = kernel execution address
* r7 = architecture ID
* r8 = atags pointer
*/
mov r0, r4
mov r1, sp @ malloc space above stack
add r2, sp, #0x10000 @ 64k max
mov r3, r7
bl decompress_kernel mov r0, r7
mov r1, r8
bl DispDeviceTree
mov r0, r4
mov r1, sp
居然打印出了，说明我破坏了寄存器里面的值，导致连设备树都找不到了，machine id的值不需要关心，因为我们是用dts来匹配的，现在的kernel是支持两种匹配方式的，所以在两种都找不到的情况下就报错了，相信以后kernel会完全删除tags的方式的。
Starting kernel ... Uncompressing Linux... done, booting the kernel.
Machid=0362 dev tree: Error: unrecognized/unsupported device tree compatible list:
[ 'samsung,s3c2440' 'samsung,jz2440' ] Available machine support: ID (hex) NAME
00000400 AML_M5900
0000014b Simtec-BAST
0000015b IPAQ-H1940
0000039f Acer-N35
00000290 Acer-N30
000002a8 Nex Vision - Otom 1.1
00000454 QT2410
000000c1 SMDK2410
000005b4 TCT_HAMMER
000001db Thorcom-VR1000
000005d2 JIVE
000003fe SMDK2413
000003f1 SMDK2412
00000377 S3C2413
00000474 VSTMS
00000695 SMDK2416
000002de Simtec-Anubis
00000707 AT2440EVB
000007cf MINI2440
000002a9 NexVision - Nexcoder 2440
0000034a Simtec-OSIRIS
00000250 IPAQ-RX3715
00000518 GTA02
000003b8 HP iPAQ RX1950
0000043c SMDK2443 Please check your kernel config and/or bootloader.
后来我将misc.c和head.S还原，还是打印了这些信息，挺好的。
SMDK2440 # bootm 30000000 - 31000000
## Booting kernel from Legacy Image at 30000000 ...
Image Name: Linux-4.15.1-gc1aaab686-dirty
Image Type: ARM Linux Kernel Image (uncompressed)
Data Size: 3488904 Bytes = 3.3 MiB
Load Address: 30008000
Entry Point: 30008000
Verifying Checksum ... OK
## Flattened Device Tree blob at 31000000
Booting using the fdt blob at 0x31000000
Loading Kernel Image ... OK
Loading Device Tree to 33ba6000, end 33baa506 ... OK Starting kernel ... Uncompressing Linux... done, booting the kernel.
bootcmd line:
arch/arm/kernel/devtree.c:setup_machine_fdt __machine_arch_type=ffffffff
bootcmd line:noinitrd console=ttySAC0,115200 root=/dev/mtdblock3 rootfstype=
jffs2 earlyprintk find fdt,and tags
r1=0xffffffff, r2=0x33ba6000
machine name:Samsung S3C2440 (Flattened Device Tree)
Booting Linux on physical CPU 0x0
Linux version 4.15.1-gc1aaab686-dirty (kent@hu) (gcc version 4.4.3 (ctng-1.6.1
)) #27 Mon Sep 3 22:21:31 CST 2018
CPU: ARM920T [41129200] revision 0 (ARMv4T), cr=c000717f
CPU: VIVT data cache, VIVT instruction cache
OF: fdt: Machine model: JZ2440
bootcmd line:
arch/arm/kernel/devtree.c:setup_machine_fdt __machine_arch_type=ffffffff
bootcmd line:noinitrd console=ttySAC0,115200 root=/dev/mtdblock3 rootfstype=
jffs2 earlyprintk find fdt,and tags
r1=0xffffffff, r2=0x33ba6000
machine name:Samsung S3C2440 (Flattened Device Tree)
bootconsole [earlycon0] enabled
Memory policy: Data cache writeback
CPU S3C2440A (id 0x32440001)
DT missing boot CPU MPIDR[23:0], fall back to default cpu_logical_map
random: fast init done
Built 1 zonelists, mobility grouping on. Total pages: 16256
Kernel command line: noinitrd console=ttySAC0,115200 root=/dev/mtdblock3
rootfstype=jffs2 earlyprintk
Dentry cache hash table entries: 8192 (order: 3, 32768 bytes)
Inode-cache hash table entries: 4096 (order: 2, 16384 bytes)
Memory: 57764K/65536K available (5319K kernel code, 216K rwdata, 1164K rodata
, 204K init, 203K bss, 7772K reserved, 0K cma-reserved)
Virtual kernel memory layout:
vector : 0xffff0000 - 0xffff1000 ( 4 kB)
fixmap : 0xffc00000 - 0xfff00000 (3072 kB)
vmalloc : 0xc4800000 - 0xff800000 ( 944 MB)
lowmem : 0xc0000000 - 0xc4000000 ( 64 MB)
modules : 0xbf000000 - 0xc0000000 ( 16 MB)
.text : 0x(ptrval) - 0x(ptrval) (5321 kB)
.init : 0x(ptrval) - 0x(ptrval) ( 204 kB)
.data : 0x(ptrval) - 0x(ptrval) ( 217 kB)
.bss : 0x(ptrval) - 0x(ptrval) ( 204 kB)
NR_IRQS: 103
_get_rate: could not find clock xti
sched_clock: 32 bits at 100 Hz, resolution 10000000ns, wraps every
21474836475000000ns
Console: colour dummy device 80x30
这里注意到，打印的command line不是我在dts里面定义的，我当时怀疑是不是kernel没识别dts里面的bootargs成员，因为打印出了OF: fdt: Machine model: JZ2440,说明确实是找到了设备树，于是我在arch\arm\kernel\devtree.c中的setup_machine_fdt函数里面根据实际地址和虚拟地址将内存里面的设备树以08x的形式全部打印出来了，然后跟我编译出来的dts做对比，发现确实不一样，后来怀疑是uboot传错了，于是去查uboot。
将uboot中的include/common.h里面的debug打开，这样就可以看到更多的信息，于是看到打印出了以下信息：
SMDK2440 # bootm 30000000 - 31000000
## Current stack ends at 0x33ba7ba0 * kernel: cmdline image address = 0x30000000
## Booting kernel from Legacy Image at 30000000 ...
Image Name: Linux-4.15.1-gc1aaab686-dirty
Image Type: ARM Linux Kernel Image (uncompressed)
Data Size: 3489048 Bytes = 3.3 MiB
Load Address: 30008000
Entry Point: 30008000
Verifying Checksum ... OK
kernel data at 0x30000040, len = 0x00353d18 (3489048)
## Skipping init Ramdisk
## No init Ramdisk
ramdisk start = 0x00000000, ramdisk end = 0x00000000
* fdt: cmdline image address = 0x31000000
## Checking for 'FDT'/'FDT Image' at 31000000
* fdt: raw FDT blob
## Flattened Device Tree blob at 31000000
Booting using the fdt blob at 0x31000000
of_flat_tree at 0x31000000 size 0x00001507
Initial value for argc=3
Final value for argc=3
Loading Kernel Image ... OK
kernel loaded at 0x30008000, end = 0x3035bd18
images.os.start = 0x30000000, images.os.end = 0x30353d58
images.os.load = 0x30008000, load_end = 0x3035bd18
using: FDT
## initrd_high = 0xffffffff, copy_to_ram = 1
ramdisk load start = 0x00000000, ramdisk load end = 0x00000000
## device tree at 31000000 ... 31001506 (len=17671 [0x4507])
Loading Device Tree to 33ba2000, end 33ba6506 ... OK
Initial value for argc=3
Final value for argc=3
No alias for ethernet0
## Transferring control to Linux (at address 30008000)...
Starting kernel ...
Uncompressing Linux... done, booting the kernel.
phys:33ba2000
virt:c3ba2000
最后两句是我加在arch\arm\kernel\devtree.c中的setup_machine_fdt函数里面的：
说明kernel是从uboot传给它的地址去取的dts，难道真是uboot传错dts了？
于是在uboot里面的common\image-fdt.c里的boot_relocate_fdt函数里添加打印信息，将dts全部打印出来，发现dts还是错的，而且很明显是跟在configs/smdk2440.h里面定义的CONFIG_BOOTARGS完全一样，于是猜想，是不是uboot优先取CONFIG_BOOTARGS定义的bootargs，于是将其屏蔽，将存在nand上面的环境变量全部删除，再次将编译出来的uboot.bin通过jlink烧到nor上启动，在uboot的界面下通过tftp下载kernel和dts到ddr，再次执行bootm 30000000 - 31000000
这次kernel里面打印的bootargs跟我在dts里面定义的一致，至此才敢确定的说，我的JZ2440支持设备树了。