基于tiny4412的Linux内核移植（支持device tree）（三）
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转自：http://www.cnblogs.com/pengdonglin137/p/5146791.html
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作者信息
作者: 彭东林
邮箱：pengdonglin137@163.com
QQ：405728433
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平台简介
开发板：tiny4412ADK + S700 + 4GB Flash
要移植的内核版本：Linux-4.4.0 （支持device tree）
u-boot版本：友善之臂自带的 U-Boot 2010.12 （为支持uImage启动，做了少许改动）
busybox版本：busybox 1.25
交叉编译工具链： arm-none-linux-gnueabi-gcc
（gcc version 4.8.3 20140320 (prerelease) (Sourcery CodeBench Lite 2014.05-29)）
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注意
继续上文。
到目前为止，板子已经可以起来了，接下来就可以针对板子的情况移植驱动程序了。这个放在以后再做，下面是我折腾过程中得到的一些知识，分享一下。
一、设备树反编译
在内核目录下当我们执行make dtbs后，就会在arch/arm/boot/dts下生成一些.dtb文件，那这个文件里是什么东西呢？我们可以用dtc命令反编译这些dtb文件，下面以exynos4412-tiny4412.dtb为例：
命令：
dtc -I dtb -O dtb -o tiny4412.dts arch/arm/boot/dts/exynos4412-tiny4412.dtb
然后就会生成反编译后的文件 tiny4412.dts，部分内容如下：
/dts-v1/;
/ {
#address-cells = <;0x1>;
#size-cells = <;0x1>;
interrupt-parent = <;0x1>;
compatible = "friendlyarm,tiny4412", "samsung,exynos4412", "samsung,exynos4";
model = "FriendlyARM TINY4412 board based on Exynos4412";
chosen {
stdout-path = "/serial@13800000";
bootargs = "root=/dev/ram0 rw rootfstype=ext4 console=ttySAC0,115200 init=/linuxrc earlyprintk";
};
aliases {
spi0 = "/spi@13920000";
spi1 = "/spi@13930000";
spi2 = "/spi@13940000";
i2c0 = "/i2c@13860000";
i2c1 = "/i2c@13870000";
i2c2 = "/i2c@13880000";
i2c3 = "/i2c@13890000";
i2c4 = "/i2c@138A0000";
i2c5 = "/i2c@138B0000";
i2c6 = "/i2c@138C0000";
i2c7 = "/i2c@138D0000";
i2c8 = "/i2c@138E0000";
csis0 = "/camera/csis@11880000";
csis1 = "/camera/csis@11890000";
fimc0 = "/camera/fimc@11800000";
fimc1 = "/camera/fimc@11810000";
fimc2 = "/camera/fimc@11820000";
fimc3 = "/camera/fimc@11830000";
serial0 = "/serial@13800000";
serial1 = "/serial@13810000";
serial2 = "/serial@13820000";
serial3 = "/serial@13830000";
pinctrl0 = "/pinctrl@11400000";
pinctrl1 = "/pinctrl@11000000";
pinctrl2 = "/pinctrl@03860000";
pinctrl3 = "/pinctrl@106E0000";
fimc-lite0 = "/camera/fimc-lite@12390000";
fimc-lite1 = "/camera/fimc-lite@123A0000";
mshc0 = "/mmc@12550000";
};
memory {
device_type = "memory";
reg = <0x40000000 0x40000000>;
};
clock-controller@03810000 {
compatible = "samsung,exynos4210-audss-clock";
reg = <0x3810000 0xc>;
#clock-cells = <;0x1>;
linux,phandle = <;0x2>;
phandle = <;0x2>;
};
i2s@03830000 {
这个方法对于学习设备树很有帮助。
二、在u-boot打印信息
在u-boot中很多文件中是通过debug(… …)来打印信息，默认情况下这些log是打印不出来的。这个函数的定义是在include/common.h中：
#ifdef DEBUG
#define debug(fmt,args...) printf (fmt ,##args)
#define debugX(level,fmt,args...) if (DEBUG>=level) printf(fmt,##args);
#else
#define debug(fmt,args...)
#define debugX(level,fmt,args...)
#endif /* DEBUG */
所以可以在调用debug函数的C文件的最上面添加 #define DEBUG 即可。这个方法在Linux内核以及Android当中也很常用。
三、打开Linux内核启动早期的log
有时会遇到当在u-boot中执行完bootm后，打印出start kernel后串口就没有再输出任何信息了。此时就需要打开内核早期的log：
make menuconfig
Kernel hacking --->
[*] Kernel low-level debugging functions (read help!)
Kernel low-level debugging port (Use Samsung S3C UART 0 for low-level debug)
[*] Early printk
对于earlyprintk，还需要在bootargs中添加参数earlyprintk才能生效，有了上面这几个配置，会有下面几个宏生效：
CONFIG_DEBUG_LL=y
CONFIG_DEBUG_S3C_UART0=y
CONFIG_DEBUG_LL_INCLUDE="debug/exynos.S"
CONFIG_DEBUG_UNCOMPRESS=y
CONFIG_UNCOMPRESS_INCLUDE="debug/uncompress.h"
CONFIG_EARLY_PRINTK=y
关于earlyprintk的解析在文件arch/arm/kernel/early_printk.c中：
1: extern void printch(int);
2: 3: static void early_write(const char *s, unsigned n)
4: {5: while (n-- >; 0) {
6: if (*s == '\n')
7: printch('\r');
8: printch(*s);
9: s++;
10: }
11: } 12: 13: static void early_console_write(struct console *con, const char *s, unsigned n)
14: {15: early_write(s, n);
16: }
17: 18: static struct console early_console_dev = {19: .name = "earlycon",
20: .write = early_console_write, 21: .flags = CON_PRINTBUFFER | CON_BOOT, 22: .index = -1,23: };
24: 25: static int __init setup_early_printk(char *buf)
26: {27: early_console = &;early_console_dev;
28: register_console(&;early_console_dev);
29: return 0;
30: }
31: 32: early_param("earlyprintk", setup_early_printk);
其中printch都是通过汇编语言实现的。
在arch/arm/Kconfig.debug中可以看到：
config DEBUG_LL
bool "Kernel low-level debugging functions (read help!)"
depends on DEBUG_KERNEL
help
Say Y here to include definitions of printascii, printch, printhex
in the kernel. This is helpful if you are debugging code that
executes before the console is initialized.
config DEBUG_S3C_UART0
depends on PLAT_SAMSUNG
select DEBUG_EXYNOS_UART if ARCH_EXYNOS
select DEBUG_S3C24XX_UART if ARCH_S3C24XX
select DEBUG_S5PV210_UART if ARCH_S5PV210
bool "Use Samsung S3C UART 0 for low-level debug"
help
Say Y here if you want the debug print routines to direct
their output to UART 0. The port must have been initialised
by the boot-loader before use.
config DEBUG_LL_INCLUDE
string
……
default "debug/exynos.S" if DEBUG_EXYNOS_UART
config EARLY_PRINTK
bool "Early printk"
depends on DEBUG_LL
help
Say Y here if you want to have an early console using the
kernel low-level debugging functions. Add earlyprintk to your
kernel parameters to enable this console.
从上面的信息我们可以知道：
- 在串口终端尚未注册时，内核定义了printascii、printch以及printhex用于调试；
- early console使用的也是上面定义的函数，需要在传递给内核的参数中添加earlyprintk参数
- Linux内核早期的print函数的输出串口要跟u-boot下使用的一致，即内核不再负责初始化了，让u-boot来做，所以二者一定要一致，否则那些print函数以及earlyprintk都没法输出信息；
- 可以参考arch/arm/kernel/debug.S，printascii、printch以及printhex都是在这里定义的；
- 在kernel进入C函数（start_kernel）后可以调用early_print来打印信息，它是在arch/arm/kernel/setup.c中定义的：
1: void __init early_print(const char *str, ...)
2: {3: extern void printascii(const char *);
4: char buf[256];
5: va_list ap;
6: 7: va_start(ap, str);
8: vsnprintf(buf, sizeof(buf), str, ap);
9: va_end(ap);
10: 11: #ifdef CONFIG_DEBUG_LL12: printascii(buf);
13: #endif
14: printk("%s", buf);
15: }可以看到，early_print也会调用printascii和printk，意思是用early_print打印的信息可能会重复出现在终端上（printk会缓冲一部分,当bootconsole注册后，会将printk缓冲区中的内容输出）。
上面所说的打印函数只能在内核自解压后的函数中才能使用，那么内核自解压过程中的信息是不是也可以打印呢？可以，内核自解压相关的文件在arch/arm/boot/compressed/下面，我们所熟知的：
Uncompressing Linux... done, booting the kernel.
就是这个目录下的代码打印出来的，具体代码如下：
arch/arm/boot/compressed/misc.c
1: void 2: decompress_kernel(unsigned long output_start, unsigned long free_mem_ptr_p, 3: unsigned long free_mem_ptr_end_p, 4: int arch_id) 5: { 6: ......7: putstr("Uncompressing Linux...");
8: ret = do_decompress(input_data, input_data_end - input_data,
9: output_data, error);
10: ......
11: putstr(" done, booting the kernel.\n");
12: }其中，putstr的定义如下:
1: static void putstr(const char *ptr)
2: {3: char c;
4: 5: while ((c = *ptr++) != '\0') {
6: if (c == '\n')
7: putc('\r');
8: putc(c);
9: } 10: 11: flush();
12: }putc是汇编实现的，arch/arm/boot/compressed/debug.S：
1: #include CONFIG_DEBUG_LL_INCLUDE
2: 3: ENTRY(putc) 4: addruart r1, r2, r3 5: waituart r3, r1 6: senduart r0, r1 7: busyuart r3, r1 8: mov pc, lr 9: ENDPROC(putc) 10: 11: 其中addruart的实现因soc的不同而不同，对于exynos4412，它的实现是（arch/arm/include/debug/exynos.S）：
1: .macro addruart, rp, rv, tmp 2: mrc p15, 0, \tmp, c0, c0, 0 3: and \tmp, \tmp, #0xf0 4: teq \tmp, #0xf0 @@ A15 5: ldreq \rp, =EXYNOS5_PA_UART 6: movne \rp, #EXYNOS4_PA_UART @@ EXYNOS4 7: ldr \rv, =S3C_VA_UART 8: CONFIG_DEBUG_S3C_UART != 0 9: add \rp, \rp, #(0x10000 * CONFIG_DEBUG_S3C_UART) 10: add \rv, \rv, #(0x10000 * CONFIG_DEBUG_S3C_UART)11: if
12: .endm这个函数的目的就是获得控制调试uart的寄存器的物理基地址(rp)和虚拟基地址(rv),这里也没有初始化uart的代码，所以必须跟u-boot使用的串口一致。
四、在内核自解压时dump内存
这是在调试设备树在内存中的镜像被自解压后的内核覆盖时发现的。下面是使用方法：
- 首先需要按照上面的一节配置内核打开那几个宏
- 修改arch/arm/boot/compressed/head.S，如下：
1: diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S 2: index 06e983f..7ecde2e 100644 3: --- a/arch/arm/boot/compressed/head.S 4: +++ b/arch/arm/boot/compressed/head.S 5: @@ -22,6 +22,8 @@6: * 100% relocatable. Any attempt to do so will result in a crash.
7: * Please select one of the following when turning on debugging.
8: */ 9: +#define DEBUG 10: + 11: #ifdef DEBUG 12: 13: #if defined(CONFIG_DEBUG_ICEDCC)
14: @@ -65,7 +67,7 @@ 15: .endm16: #else
17: .macro loadsp, rb, tmp 18: - addruart \rb, \tmp 19: + addruart \rb, \tmp, \tmp 20: .endm21: #endif
22: #endif
23: @@ -536,6 +538,24 @@ not_relocated: mov r0, #0 24: * r7 = architecture ID 25: * r8 = atags pointer 26: */ 27: + stmfd sp!, {r0-r3, r10-r12, lr} 28: + kputc #'\n' 29: + kputc #'a' 30: + kputc #'t' 31: + kputc #'a' 32: + kputc #'g' 33: + kputc #'s' 34: + kputc #':' 35: + kputc #' ' 36: + kputc #'0' 37: + kputc #'x' 38: + kphex r8, 8 /* atags pointer */ 39: + kputc #'\n' 40: + mov r0, r8 41: + bl memdump /* dump 256 bytes at start of kernel */ 42: + kputc #'\n' 43: + ldmfd sp!, {r0-r3, r10-r12, lr} 44: + 45: mov r0, r4 46: mov r1, sp @ malloc space above stack 47: add r2, sp, #0x10000 @ 64k max 48: @@ -546,6 +566,26 @@ not_relocated: mov r0, #0 49: mov r1, r7 @ restore architecture number 50: mov r2, r8 @ restore atags pointer 51: 52: + stmfd sp!, {r0-r3, r10-r12, lr} 53: + kputc #'\n' 54: + kputc #'\n' 55: + kputc #'a' 56: + kputc #'t' 57: + kputc #'a' 58: + kputc #'g' 59: + kputc #'s' 60: + kputc #':' 61: + kputc #' ' 62: + kputc #'0' 63: + kputc #'x' 64: + kphex r8, 8 /* atags pointer */ 65: + kputc #'\n' 66: + mov r0, r8 67: + bl memdump /* dump 256 bytes at start of kernel */ 68: + kputc #'\n' 69: + ldmfd sp!, {r0-r3, r10-r12, lr} 70: + 71: + 72: #ifdef CONFIG_ARM_VIRT_EXT 73: mrs r0, spsr @ Get saved CPU boot mode 74: and r0, r0, #MODE_MASK可以使用kputc打印出一个字符，kphex用于打印一个指定位宽的十六进制数，将需要dump的内粗地址存放入r0，然后调用memdump即可，memdump会dump出256B的内容。u-boot在跳转到内核的时候传递三个参数，分别给了r0、r1、r2，在没有设备树之前，传给r0,r1和r2的分别是0，machid以及u-boot传给Linux内核参数的地址（如0x40000100）,在有了设备树之后，传给r0的是0，传给r1的值无所谓，传给r2的是设备树镜像在内存中的地址。效果如下：
U-Boot 2010.12-00000-gb391276-dirty (Jan 17 2016 - 06:03:22) for TINY4412CPU: S5PC220 [Samsung SOC on SMP Platform Base on ARM CortexA9]
APLL = 1400MHz, MPLL = 800MHz
Board: TINY4412
DRAM: 1023 MiB
vdd_arm: 1.2
vdd_int: 1.0
vdd_mif: 1.1
BL1 version: N/A (TrustZone Enabled BSP)
Checking Boot Mode ... SDMMC
REVISION: 1.1
MMC Device 0: 3803 MB
MMC Device 1: 3728 MB
MMC Device 2: N/A
*** Warning - using default environmentNet: No ethernet found.
Hit any key to stop autoboot: 0 TINY4412 #
TINY4412 # dnw 0x40000000
OTG cable Connected!
Now, Waiting for DNW to transmit data
Download Done!! Download Address: 0x40000000, Download Filesize:0x43bde8
Checksum is being calculated.....
Checksum O.K.
TINY4412 # dnw 0x41000000
OTG cable Connected!
Now, Waiting for DNW to transmit data
Download Done!! Download Address: 0x41000000, Download Filesize:0x27752e
Checksum is being calculated...
Checksum O.K.
TINY4412 # dnw 0x42000000
OTG cable Connected!
Now, Waiting for DNW to transmit data
Download Done!! Download Address: 0x42000000, Download Filesize:0xa53a
Checksum is being calculated.
Checksum O.K.
TINY4412 # bootm 0x40000000 0x41000000 0x42000000
## Booting kernel from Legacy Image at 40000000 ...
Image Name: Linux-4.4.0-gbd49c0f-dirty
Image Type: ARM Linux Kernel Image (uncompressed)
Data Size: 4439464 Bytes = 4335 KiB
Load Address: 40008000
Entry Point: 40008000
Verifying Checksum ... OK
## Loading init Ramdisk from Legacy Image at 41000000 ...
Image Name: ramdisk
Image Type: ARM Linux RAMDisk Image (gzip compressed)
Data Size: 2585838 Bytes = 2525 KiB
Load Address: 00000000
Entry Point: 00000000
Verifying Checksum ... OK
## Flattened Device Tree blob at 42000000
Booting using the fdt blob at 0x42000000
Loading Kernel Image ... OK
OK
## Loading init Ramdisk from Legacy Image at 41000000 ...
Image Name: ramdisk
Image Type: ARM Linux RAMDisk Image (gzip compressed)
Data Size: 2585838 Bytes = 2525 KiB
Load Address: 00000000
Entry Point: 00000000
Verifying Checksum ... OK
Loading Ramdisk to 43a84000, end 43cfb4ee ... OK Loading Device Tree to 413f2000, end 413ff539 ... OKStarting kernel ...
atags: 0x413F2000
413F2000: EDFE0DD0 3AD50000 48000000 849E0000 28000000 11000000 10000000 00000000
413F2020: 22070000 3C9E0000 00000000 0040A843 00000000 EF742700 00000000 00000000
413F2040: 00000000 00000000 01000000 00000000 03000000 04000000 00000000 01000000
413F2060: 03000000 04000000 0F000000 01000000 03000000 04000000 1B000000 01000000
413F2080: 03000000 38000000 2C000000 65697266 796C646E 2C6D7261 796E6974 32313434
413F20A0: 6D617300 676E7573 7978652C 34736F6E 00323134 736D6173 2C676E75 6E797865
413F20C0: 0034736F 03000000 2F000000 37000000 65697246 796C646E 204D5241 594E4954
413F20E0: 32313434 616F6220 62206472 64657361 206E6F20 6E797845 3434736F 00003231
Uncompressing Linux... done, booting the kernel.
atags: 0x413F2000
413F2000: EDFE0DD0 3AD50000 48000000 849E0000 28000000 11000000 10000000 00000000
413F2020: 22070000 3C9E0000 00000000 0040A843 00000000 EF742700 00000000 00000000
413F2040: 00000000 00000000 01000000 00000000 03000000 04000000 00000000 01000000
413F2060: 03000000 04000000 0F000000 01000000 03000000 04000000 1B000000 01000000
413F2080: 03000000 38000000 2C000000 65697266 796C646E 2C6D7261 796E6974 32313434
413F20A0: 6D617300 676E7573 7978652C 34736F6E 00323134 736D6173 2C676E75 6E797865
413F20C0: 0034736F 03000000 2F000000 37000000 65697246 796C646E 204D5241 594E4954
413F20E0: 32313434 616F6220 62206472 64657361 206E6F20 6E797845 3434736F 00003231
[ 0.000000] Booting Linux on physical CPU 0xa00
[ 0.000000] Linux version 4.4.0-gbd49c0f-dirty (root@ubuntu) (gcc version 4.8.3 20140320 (prerelease) (Sourcery CodeBench Lite 2014.05-29) ) #25 SMP PREEMPT Tue Jan 19 05:50:47 PST 2016
[ 0.000000] CPU: ARMv7 Processor [413fc090] revision 0 (ARMv7), cr=10c5387d
[ 0.000000] CPU: PIPT / VIPT nonaliasing data cache, VIPT aliasing instruction cache
[ 0.000000] Machine model: FriendlyARM TINY4412 board based on Exynos4412
[ 0.000000] bootconsole [earlycon0] enabled
[ 0.000000] cma: Reserved 64 MiB at 0x7bc00000
[ 0.000000] Memory policy: Data cache writealloc
[ 0.000000] Samsung CPU ID: 0xe4412011
[ 0.000000] PERCPU: Embedded 12 pages/cpu @ef79b000 s18816 r8192 d22144 u49152
[ 0.000000] Built 1 zonelists in Zone order, mobility grouping on. Total pages: 260352[ 0.000000] Kernel command line: root=/dev/ram0 rw rootfstype=ext4 console=ttySAC0,115200 init=/linuxrc earlyprintk
[ 0.000000] PID hash table entries: 4096 (order: 2, 16384 bytes)
[ 0.000000] Dentry cache hash table entries: 131072 (order: 7, 524288 bytes)
[ 0.000000] Inode-cache hash table entries: 65536 (order: 6, 262144 bytes)
[ 0.000000] Memory: 960824K/1047552K available (5867K kernel code, 293K rwdata, 2288K rodata, 440K init, 315K bss, 21192K reserved, 65536K cma-reserved, 195584K highmem)
[ 0.000000] Virtual kernel memory layout:
[ 0.000000] vector : 0xffff0000 - 0xffff1000 ( 4 kB)
[ 0.000000] fixmap : 0xffc00000 - 0xfff00000 (3072 kB)
[ 0.000000] vmalloc : 0xf0800000 - 0xff800000 ( 240 MB)
[ 0.000000] lowmem : 0xc0000000 - 0xf0000000 ( 768 MB)
[ 0.000000] pkmap : 0xbfe00000 - 0xc0000000 ( 2 MB)
[ 0.000000] modules : 0xbf000000 - 0xbfe00000 ( 14 MB)
[ 0.000000] .text : 0xc0008000 - 0xc07ff200 (8157 kB)
[ 0.000000] .init : 0xc0800000 - 0xc086e000 ( 440 kB)
[ 0.000000] .data : 0xc086e000 - 0xc08b7418 ( 294 kB)
[ 0.000000] .bss : 0xc08ba000 - 0xc0908d28 ( 316 kB)
可以看到 Uncompressing Linux... done, booting the kernel.前后就是dump出的设备树的内容（大小端 可能有些问题）.
五、CONFIG_ARM_APPENDED_DTB
这个宏是Linux内核中的，它的作用是支持zImage+dtb的启动方式。为什么要有种方式呢？因为很多厂家都有自己的bootloader，但是这些bootloader并不都一定支持设备树，为了实现支持设备树启动，就引入了这种启动方式，即将编译出的zImage和编译出的设备树镜像文件拼成一个新的镜像，在内核的自解压代码中会识别到，不会出现自解压时导致设备树被覆盖，具体实现如下（arch/arm/boot/compressed/head.S）
mov r5, #0 @ init dtb size to 0#ifdef CONFIG_ARM_APPENDED_DTB
/*
* r0 = delta
* r2 = BSS start
* r3 = BSS end
* r4 = final kernel address (possibly with LSB set)* r5 = appended dtb size (still unknown)
* r6 = _edata
* r7 = architecture ID
* r8 = atags/device tree pointer
* r9 = size of decompressed image
* r10 = end of this image, including bss/stack/malloc space if non XIP* r11 = GOT start
* r12 = GOT end
* sp = stack pointer
*
* if there are device trees (dtb) appended to zImage, advance r10 so that the
* dtb data will get relocated along with the kernel if necessary.
*/
ldr lr, [r6, #0]
#ifndef __ARMEB__
ldr r1, =0xedfe0dd0 @ sig is 0xd00dfeed big endian
#elseldr r1, =0xd00dfeed
#endifcmp lr, r1
bne dtb_check_done @ not found
#ifdef CONFIG_ARM_ATAG_DTB_COMPAT
/*
* OK... Let's do some funky business here.* If we do have a DTB appended to zImage, and we do have
* an ATAG list around, we want the later to be translated* and folded into the former here. No GOT fixup has occurred
* yet, but none of the code we're about to call uses any * global variable.*/
/* Get the initial DTB size */
ldr r5, [r6, #4]
#ifndef __ARMEB__
/* convert to little endian */eor r1, r5, r5, ror #16
bic r1, r1, #0x00ff0000
mov r5, r5, ror #8
eor r5, r5, r1, lsr #8
#endif/* 50% DTB growth should be good enough */
add r5, r5, r5, lsr #1
/* preserve 64-bit alignment */
add r5, r5, #7
bic r5, r5, #7
/* clamp to 32KB min and 1MB max */cmp r5, #(1 <;< 15)movlo r5, #(1 <;< 15)cmp r5, #(1 <;< 20)movhi r5, #(1 <;< 20)/* temporarily relocate the stack past the DTB work space */
add sp, sp, r5
stmfd sp!, {r0-r3, ip, lr}mov r0, r8
mov r1, r6
mov r2, r5
bl atags_to_fdt
/*
* If returned value is 1, there is no ATAG at the location* pointed by r8. Try the typical 0x100 offset from start
* of RAM and hope for the best.*/
cmp r0, #1
sub r0, r4, #TEXT_OFFSET
bic r0, r0, #1
add r0, r0, #0x100
mov r1, r6
mov r2, r5
bleq atags_to_fdt
ldmfd sp!, {r0-r3, ip, lr}sub sp, sp, r5
#endifmov r8, r6 @ use the appended device tree
/*
* Make sure that the DTB doesn't end up in the final* kernel's .bss area. To do so, we adjust the decompressed
* kernel size to compensate if that .bss size is larger
* than the relocated code.
*/
ldr r5, =_kernel_bss_size
adr r1, wont_overwrite
sub r1, r6, r1
subs r1, r5, r1
addhi r9, r9, r1
/* Get the current DTB size */
ldr r5, [r6, #4]
#ifndef __ARMEB__
/* convert r5 (dtb size) to little endian */eor r1, r5, r5, ror #16
bic r1, r1, #0x00ff0000
mov r5, r5, ror #8
eor r5, r5, r1, lsr #8
#endif/* preserve 64-bit alignment */
add r5, r5, #7
bic r5, r5, #7
/* relocate some pointers past the appended dtb */
add r6, r6, r5
add r10, r10, r5
add sp, sp, r5
dtb_check_done:
#endif
拼接方法：
cat zImage dts/exynos4412-tiny4412.dtb > dtbImage
也可以修改内核编译系统，在编译完成后自动实现拼接，可以参考下面的博文实现：
http://www.cnblogs.com/pengdonglin137/p/5134364.html
下面是使用dtbImage启动的方法：
1、修改设备树 arch/arm/boot/dts/exynos4412-tiny4412.dts
diff --git a/arch/arm/boot/dts/exynos4412-tiny4412.dts b/arch/arm/boot/dts/exynos4412-tiny4412.dts
index 4840bbd..1e33ede 100644
--- a/arch/arm/boot/dts/exynos4412-tiny4412.dts
+++ b/arch/arm/boot/dts/exynos4412-tiny4412.dts
@@ -21,6 +21,7 @@
chosen { stdout-path = &;serial_0;+ bootargs = "root=/dev/ram0 rw rootfstype=ext4 ramdisk=8192 initrd=0x41000000,8M console=ttySAC0,115200 init=/linuxrc mem=1024M" }; memory {@@ -78,7 +79,7 @@
bus-width = <;4>; pinctrl-0 = <;&sd2_clk &sd2_cmd &sd2_cd &sd2_bus4>;pinctrl-names = "default";
- status = "okay";+ status = "disabled";
}; &;serial_0 {2、编译设备树 make dtbs，将生成的.dtb跟zImag拼接起来生成dtbImage
3、使用ramdisk启动，目前不能使用ramdisk.img，还不知道为什么。
4、启动开发板，进入u-boot命令行模式，执行如下命令：
在u-boot里执行下载dtbImage的命令： dnw 0x40008000
在开发机上执行： dnw dtbImage
在u-boot里执行下载ramdisk的命令：dnw 0x41000000
在开发机上执行： dnw ramdisk
启动内核： bootm 0x40008000 (u-boot不识别未压缩的ramdisk，ramdisk的地址在bootargs中指定为0x41000000，而且上面我们已经把ramdisk下载到0x41000000了)
下面是完整的log：
U-Boot 2010.12-00000-gb391276-dirty (Jan 17 2016 - 06:03:22) for TINY4412CPU: S5PC220 [Samsung SOC on SMP Platform Base on ARM CortexA9]
APLL = 1400MHz, MPLL = 800MHz
Board: TINY4412
DRAM: 1023 MiB
vdd_arm: 1.2
vdd_int: 1.0
vdd_mif: 1.1
BL1 version: N/A (TrustZone Enabled BSP)
Checking Boot Mode ... SDMMC
REVISION: 1.1
MMC Device 0: 3803 MB
MMC Device 1: 3728 MB
MMC Device 2: N/A
*** Warning - using default environmentNet: No ethernet found.
Hit any key to stop autoboot: 0 TINY4412 # dnw 0x40008000
OTG cable Connected!
Now, Waiting for DNW to transmit data
Download Done!! Download Address: 0x40008000, Download Filesize:0x446302
Checksum is being calculated.....
Checksum O.K.
TINY4412 # dnw 0x41000000
OTG cable Connected!
Now, Waiting for DNW to transmit data
Download Done!! Download Address: 0x41000000, Download Filesize:0x800000
Checksum is being calculated.........
Checksum O.K.
TINY4412 # bootm 0x40008000
Boot with zImageStarting kernel ...
atags: 0x40CF68E8
40CF68E8: EDFE0DD0 72A50000 38000000 749E0000 28000000 11000000 10000000 00000000
40CF6908: FE060000 3C9E0000 00000000 00000000 00000000 00000000 01000000 00000000
40CF6928: 03000000 04000000 00000000 01000000 03000000 04000000 0F000000 01000000
40CF6948: 03000000 04000000 1B000000 01000000 03000000 38000000 2C000000 65697266
40CF6968: 796C646E 2C6D7261 796E6974 32313434 6D617300 676E7573 7978652C 34736F6E
40CF6988: 00323134 736D6173 2C676E75 6E797865 0034736F 03000000 2F000000 37000000
40CF69A8: 65697246 796C646E 204D5241 594E4954 32313434 616F6220 62206472 64657361
40CF69C8: 206E6F20 6E797845 3434736F 00003231 01000000 736F6863 00006E65 03000000
Uncompressing Linux... done, booting the kernel.
atags: 0x40CF68E8
40CF68E8: EDFE0DD0 72A50000 38000000 749E0000 28000000 11000000 10000000 00000000
40CF6908: FE060000 3C9E0000 00000000 00000000 00000000 00000000 01000000 00000000
40CF6928: 03000000 04000000 00000000 01000000 03000000 04000000 0F000000 01000000
40CF6948: 03000000 04000000 1B000000 01000000 03000000 38000000 2C000000 65697266
40CF6968: 796C646E 2C6D7261 796E6974 32313434 6D617300 676E7573 7978652C 34736F6E
40CF6988: 00323134 736D6173 2C676E75 6E797865 0034736F 03000000 2F000000 37000000
40CF69A8: 65697246 796C646E 204D5241 594E4954 32313434 616F6220 62206472 64657361
40CF69C8: 206E6F20 6E797845 3434736F 00003231 01000000 736F6863 00006E65 03000000
[ 0.000000] Booting Linux on physical CPU 0xa00
[ 0.000000] Linux version 4.4.0-gbd49c0f-dirty (root@ubuntu) (gcc version 4.8.3 20140320 (prerelease) (Sourcery CodeBench Lite 2014.05-29) ) #25 SMP PREEMPT Tue Jan 19 05:50:47 PST 2016
[ 0.000000] CPU: ARMv7 Processor [413fc090] revision 0 (ARMv7), cr=10c5387d
[ 0.000000] CPU: PIPT / VIPT nonaliasing data cache, VIPT aliasing instruction cache
[ 0.000000] Machine model: FriendlyARM TINY4412 board based on Exynos4412
[ 0.000000] cma: Reserved 64 MiB at 0x7c000000
[ 0.000000] Memory policy: Data cache writealloc
[ 0.000000] Samsung CPU ID: 0xe4412011
[ 0.000000] PERCPU: Embedded 12 pages/cpu @ef79b000 s18816 r8192 d22144 u49152
[ 0.000000] Built 1 zonelists in Zone order, mobility grouping on. Total pages: 260608[ 0.000000] Kernel command line: root=/dev/ram0 rw rootfstype=ext4 ramdisk=8192 initrd=0x41000000,8M console=ttySAC0,115200 init=/linuxrc mem=1024M
[ 0.000000] PID hash table entries: 4096 (order: 2, 16384 bytes)
[ 0.000000] Dentry cache hash table entries: 131072 (order: 7, 524288 bytes)
[ 0.000000] Inode-cache hash table entries: 65536 (order: 6, 262144 bytes)
[ 0.000000] Memory: 956196K/1048576K available (5867K kernel code, 293K rwdata, 2288K rodata, 440K init, 315K bss, 26844K reserved, 65536K cma-reserved, 196608K highmem)
[ 0.000000] Virtual kernel memory layout:
[ 0.000000] vector : 0xffff0000 - 0xffff1000 ( 4 kB)
[ 0.000000] fixmap : 0xffc00000 - 0xfff00000 (3072 kB)
[ 0.000000] vmalloc : 0xf0800000 - 0xff800000 ( 240 MB)
[ 0.000000] lowmem : 0xc0000000 - 0xf0000000 ( 768 MB)
[ 0.000000] pkmap : 0xbfe00000 - 0xc0000000 ( 2 MB)
[ 0.000000] modules : 0xbf000000 - 0xbfe00000 ( 14 MB)
[ 0.000000] .text : 0xc0008000 - 0xc07ff200 (8157 kB)
[ 0.000000] .init : 0xc0800000 - 0xc086e000 ( 440 kB)
[ 0.000000] .data : 0xc086e000 - 0xc08b7418 ( 294 kB)
[ 0.000000] .bss : 0xc08ba000 - 0xc0908d28 ( 316 kB)
[ 0.000000] SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=4, Nodes=1
[ 0.000000] Preemptible hierarchical RCU implementation.
[ 0.000000] Build-time adjustment of leaf fanout to 32.[ 0.000000] RCU restricting CPUs from NR_CPUS=8 to nr_cpu_ids=4.[ 0.000000] RCU: Adjusting geometry for rcu_fanout_leaf=32, nr_cpu_ids=4[ 0.000000] NR_IRQS:16 nr_irqs:16 16
[ 0.000000] GIC physical location is 0x10490000
[ 0.000000] L2C: platform modifies aux control register: 0x02070000 ->; 0x3e470001[ 0.000000] L2C: platform provided aux values permit register corruption.
[ 0.000000] L2C: DT/platform modifies aux control register: 0x02070000 ->; 0x3e470001[ 0.000000] L2C-310 enabling early BRESP for Cortex-A9[ 0.000000] L2C-310: enabling full line of zeros but not enabled in Cortex-A9[ 0.000000] L2C-310 dynamic clock gating enabled, standby mode enabled
[ 0.000000] L2C-310 cache controller enabled, 16 ways, 1024 kB
[ 0.000000] L2C-310: CACHE_ID 0x4100c4c8, AUX_CTRL 0x4e470001
[ 0.000000] Exynos4x12 clocks: sclk_apll = 466666667, sclk_mpll = 800000000
[ 0.000000] sclk_epll = 96000000, sclk_vpll = 108000000, arm_clk = 1400000000
[ 0.000000] Switching to timer-based delay loop, resolution 41ns[ 0.000000] clocksource: mct-frc: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 79635851949 ns
[ 0.000003] sched_clock: 32 bits at 24MHz, resolution 41ns, wraps every 89478484971ns
[ 0.000122] Console: colour dummy device 80x30
[ 0.000135] Calibrating delay loop (skipped), value calculated using timer frequency.. 48.00 BogoMIPS (lpj=120000)
[ 0.000144] pid_max: default: 32768 minimum: 301[ 0.000209] Mount-cache hash table entries: 2048 (order: 1, 8192 bytes)
[ 0.000217] Mountpoint-cache hash table entries: 2048 (order: 1, 8192 bytes)
[ 0.000586] CPU: Testing write buffer coherency: ok
[ 0.000772] CPU0: thread -1, cpu 0, socket 10, mpidr 80000a00
[ 0.000999] Setting up static identity map for 0x400082c0 - 0x40008318[ 0.045048] CPU1: thread -1, cpu 1, socket 10, mpidr 80000a01
[ 0.060041] CPU2: thread -1, cpu 2, socket 10, mpidr 80000a02
[ 0.075042] CPU3: thread -1, cpu 3, socket 10, mpidr 80000a03
[ 0.075082] Brought up 4 CPUs
[ 0.075096] SMP: Total of 4 processors activated (192.00 BogoMIPS).
[ 0.075101] CPU: All CPU(s) started in SVC mode.[ 0.075611] devtmpfs: initialized
[ 0.084566] VFP support v0.3: implementor 41 architecture 3 part 30 variant 9 rev 4
[ 0.084839] lcd0-power-domain@10023C80 has as child subdomain: tv-power-domain@10023C20.
[ 0.085225] clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 9556302231375000 ns
[ 0.087164] pinctrl core: initialized pinctrl subsystem
[ 0.087929] NET: Registered protocol family 16
[ 0.089226] DMA: preallocated 256 KiB pool for atomic coherent allocations[ 0.105005] cpuidle: using governor ladder
[ 0.120000] cpuidle: using governor menu
[ 0.120747] exynos-audss-clk 3810000.clock-controller: setup completed
[ 0.157138] SCSI subsystem initialized
[ 0.157506] usbcore: registered new interface driver usbfs
[ 0.157580] usbcore: registered new interface driver hub
[ 0.157660] usbcore: registered new device driver usb
[ 0.158780] Advanced Linux Sound Architecture Driver Initialized.
[ 0.159857] clocksource: Switched to clocksource mct-frc[ 0.169153] missing cooling_device property
[ 0.169163] failed to build thermal zone cpu-thermal: -2[ 0.169260] NET: Registered protocol family 2
[ 0.169627] TCP established hash table entries: 8192 (order: 3, 32768 bytes)
[ 0.169686] TCP bind hash table entries: 8192 (order: 5, 163840 bytes)
[ 0.169803] TCP: Hash tables configured (established 8192 bind 8192)
[ 0.169921] UDP hash table entries: 512 (order: 2, 24576 bytes)
[ 0.169950] UDP-Lite hash table entries: 512 (order: 2, 24576 bytes)
[ 0.170092] NET: Registered protocol family 1
[ 0.170297] RPC: Registered named UNIX socket transport module.
[ 0.170305] RPC: Registered udp transport module.
[ 0.170310] RPC: Registered tcp transport module.
[ 0.170315] RPC: Registered tcp NFSv4.1 backchannel transport module.
[ 0.170461] Trying to unpack rootfs image as initramfs...[ 0.170628] rootfs image is not initramfs (junk in compressed archive); looks like an initrd
[ 0.193515] Freeing initrd memory: 8192K (c1000000 - c1800000)
[ 0.194996] futex hash table entries: 1024 (order: 4, 65536 bytes)
[ 0.204233] romfs: ROMFS MTD (C) 2007 Red Hat, Inc.
[ 0.204924] bounce: pool size: 64 pages
[ 0.204936] io scheduler noop registered
[ 0.204945] io scheduler deadline registered
[ 0.205116] io scheduler cfq registered (default)[ 0.209955] dma-pl330 12680000.pdma: Loaded driver for PL330 DMAC-141330[ 0.209967] dma-pl330 12680000.pdma: DBUFF-32x4bytes Num_Chans-8 Num_Peri-32 Num_Events-32
[ 0.213022] dma-pl330 12690000.pdma: Loaded driver for PL330 DMAC-141330[ 0.213032] dma-pl330 12690000.pdma: DBUFF-32x4bytes Num_Chans-8 Num_Peri-32 Num_Events-32
[ 0.213909] dma-pl330 12850000.mdma: Loaded driver for PL330 DMAC-141330[ 0.213919] dma-pl330 12850000.mdma: DBUFF-64x8bytes Num_Chans-8 Num_Peri-1 Num_Events-32
[ 0.271176] Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled
[ 0.272413] 13800000.serial: ttySAC0 at MMIO 0x13800000 (irq = 44, base_baud = 0) is a S3C6400/10
[ 0.908554] console [ttySAC0] enabled
[ 0.912530] 13810000.serial: ttySAC1 at MMIO 0x13810000 (irq = 45, base_baud = 0) is a S3C6400/10
[ 0.921327] 13820000.serial: ttySAC2 at MMIO 0x13820000 (irq = 46, base_baud = 0) is a S3C6400/10
[ 0.930171] 13830000.serial: ttySAC3 at MMIO 0x13830000 (irq = 47, base_baud = 0) is a S3C6400/10
[ 0.939720] [drm] Initialized drm 1.1.0 20060810
[ 0.953371] brd: module loaded
[ 0.958359] loop: module loaded
[ 0.959171] usbcore: registered new interface driver r8152
[ 0.959302] usbcore: registered new interface driver asix
[ 0.960434] usbcore: registered new interface driver ax88179_178a
[ 0.966498] usbcore: registered new interface driver cdc_ether
[ 0.972325] usbcore: registered new interface driver dm9601
[ 0.977884] usbcore: registered new interface driver smsc75xx
[ 0.983611] usbcore: registered new interface driver smsc95xx
[ 0.989325] usbcore: registered new interface driver net1080
[ 0.994965] usbcore: registered new interface driver cdc_subset
[ 1.000873] usbcore: registered new interface driver zaurus
[ 1.006454] usbcore: registered new interface driver cdc_ncm
[ 1.012397] ehci_hcd: USB 2.0 'Enhanced' Host Controller (EHCI) Driver
[ 1.018528] ehci-exynos: EHCI EXYNOS driver
[ 1.022808] ohci_hcd: USB 1.1 'Open' Host Controller (OHCI) Driver
[ 1.028850] ohci-exynos: OHCI EXYNOS driver
[ 1.033363] usbcore: registered new interface driver usb-storage
[ 1.039544] mousedev: PS/2 mouse device common for all mice[ 1.045326] s3c-rtc 10070000.rtc: failed to find rtc source clock[ 1.050645] s3c-rtc: probe of 10070000.rtc failed with error -2[ 1.056739] i2c /dev entries driver
[ 1.062046] device-mapper: ioctl: 4.34.0-ioctl (2015-10-28) initialised: dm-devel@redhat.com
[ 1.069226] sdhci: Secure Digital Host Controller Interface driver
[ 1.074585] sdhci: Copyright(c) Pierre Ossman
[ 1.079056] Synopsys Designware Multimedia Card Interface Driver
[ 1.086865] usbcore: registered new interface driver usbhid
[ 1.090471] usbhid: USB HID core driver
[ 1.097222] NET: Registered protocol family 10
[ 1.099233] sit: IPv6 over IPv4 tunneling driver
[ 1.103848] NET: Registered protocol family 17
[ 1.107765] NET: Registered protocol family 15
[ 1.112340] Registering SWP/SWPB emulation handler
[ 1.118177] hctosys: unable to open rtc device (rtc0)[ 1.134172] ALSA device list:
[ 1.134208] No soundcards found.
[ 1.134917] RAMDISK: ext2 filesystem found at block 0
[ 1.134972] RAMDISK: Loading 8192KiB [1 disk] into ram disk... done.
[ 1.262918] EXT4-fs (ram0): mounted filesystem with red data mode. Opts: (null)[ 1.263014] VFS: Mounted root (ext4 filesystem) on device 1:0.
[ 1.263132] devtmpfs: mounted
[ 1.263411] Freeing unused kernel memory: 440K (c0800000 - c086e000)
Please press Enter to activate this console. [root@tiny4412 ]#
[root@tiny4412 ]#
0 0
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