Kindle4官方提供的Linux  kernel版本为2.6.31, 已经算是很旧版本的kernel了。当前最新版本的linux kernel为4.5，而brillo-m10-dev arm emulator所使用的版本为v4.4，对于 CPU主频只有800MHz并且RAM为256MB的Kindle4来说，跑个Brillo-m10-dev系统还是很不错的。Kindle4的优点是有PMIC(电源管理)，有fuel gauge，有WiFi，当然，还有一个USB 2.0接口，使用USB协议的adb比TCP协议的adb要好用很多(master分支上的adb已经支持TCP协议断开检查，并且解决了在执行adb reboot命令没有回应的问题)。

相关开发环境：

1. 主机系统: ubuntu-14.04 x86_64

2. 编译工具: arm-eabi-4.6 – https://android.googlesource.com/platform/prebuilts/gcc/linux-x86/arm/arm-eabi-4.6/

3. 烧机工具：fastboot – http://www.mobileread.com/forums/showthread.php?t=174923

文件结构

kindle4

|-- Fastboot-Kindle

| `-- fastboot

|-- tools

| `-- arm-eabi-4.6

|-- u-boot-2009.08

| `-- u-boot-bist-kernel

`-- v4.4

`-- arch

`-- arm

`-- boot

|-- dts

| `-- imx50-evk.dtb

`-- zImage

1. Fastboot-Kindler包含fastboot源代码及fastboot可执行程序，用于烧写u-boot-bist-kernel

2. u-boot-2009.08包含kindle4 u-boot 4.1.3版本源代码

3. tools/arm-eabi-4.6 编译u-boot代码所需要的工具链

4. v4.4 包含linux kernel v4.4源代码及编译好的zImage与imx50-evk.dtb文件

bootloader – u-boot

需要修改u-boot，以便能够引导使用Flattened Device Tree(FDT) 的kernel。相关的patch文件可以从这里下载：kindle4_v4.1.3_u-boot-bist_fdt.patch，编写u-boot-kernel-v4.4.its文件：

/*

* Simple U-boot uImage source file containing a single kernel and FDT blob

*/

/dts-v1/;

/ {

description = "i.MX508 Linux kernel and FDT blob";

#address-cells = <1>;

images {

kernel@1 {

description = "i.MX508 Linux kernel";

data = /incbin/("../v4.4/arch/arm/boot/zImage");

type = "kernel";

arch = "arm";

os = "linux";

compression = "none";

load = <0x70008000>;

entry = <0x70008000>;

hash@1 {

algo = "crc32";

};

hash@2 {

algo = "sha1";

};

};

fdt@1 {

description = "Flattened Device Tree blob";

data = /incbin/("../v4.4/arch/arm/boot/dts/imx50-evk.dtb");

type = "flat_dt";

arch = "arm";

compression = "none";

hash@1 {

algo = "crc32";

};

hash@2 {

algo = "sha1";

};

};

};

configurations {

default = "conf@1";

conf@1 {

description = "i.MX508 Boot Linux kernel with FDT blob";

kernel = "kernel@1";

fdt = "fdt@1";

};

};

};

从这里可以看到编译出来的kernel存放在../v4.4/arch/arm/boot/zImage, 而dtb文件为../v4.4/arch/arm/boot/dts/imx50-evk.dtb。

最后执行如下脚本，就可以生成我们所需要的烧机文件：u-boot-bist-kernel

#! /bin/bash

set -e

TP="`pwd`/../tools/arm-eabi-4.6"

if [ ! -f include/config.h ] ; then

CROSS_COMPILE=${TP}/bin/arm-eabi- ARCH=arm TYPE=bist make imx50_yoshi_bist_config

fi

CROSS_COMPILE=${TP}/bin/arm-eabi- ARCH=arm TYPE=bist make $@

if [ -f u-boot.bin ] ; then

tools/mkimage -A arm -O linux -T kernel -C none -a 0x79800000 -e 0x79800000 -n 'u-boot-bist' -d u-boot.bin u-boot-bist-kernel

tools/mkimage -f u-boot-kernel-v4.4.its u-boot-kernel-v4.4

dd if=u-boot-kernel-v4.4 of=u-boot-bist-kernel bs=$((1024*1024)) seek=1

fi

NOTE：由于生成最终的u-boot-bist-kernel文件需要zImage与imx50-vvk.dtb，所以在执行这个脚本时需要保证这两个文件已经存在。

执行如下命令将u-boot-bist-kernel写入到kernel分区：

hzak@B85RPI:~/kindle4/u-boot-2009.08$ ../Fastboot-Kindle/fastboot flash kernel u-boot-bist-kernel && ../Fastboot-Kindle/fastboot reboot

系统重启后会自动进入我们编译出来的u-boot – bist系统，这时候执行如下命令可以正常启动linux系统：

...

In: serial

Out: serial

Err: serial

POST done in 1 ms

Battery voltage: 3712 mV

bist > bootm 0x141000

## Booting kernel from FIT Image at 7a000000 ...

Using 'conf@1' configuration

Trying 'kernel@1' kernel subimage

Description: i.MX508 Linux kernel

Type: Kernel Image

Compression: uncompressed

Data Start: 0x7a0000dc

Data Size: 4240184 Bytes = 4 MB

Architecture: ARM

OS: Linux

Load Address: 0x70008000

Entry Point: 0x70008000

Hash algo: crc32

Hash value: d85b369e

Hash algo: sha1

Hash value: 363136b407684d3d58119823f819501f9f254399

Verifying Hash Integrity ... crc32+ sha1+ OK

## Flattened Device Tree from FIT Image at 7a000000

Using 'conf@1' configuration

Trying 'fdt@1' FDT blob subimage

Description: Flattened Device Tree blob

Type: Flat Device Tree

Compression: uncompressed

Data Start: 0x7a40b53c

Data Size: 10230 Bytes = 10 kB

Architecture: ARM

Hash algo: crc32

Hash value: 682b5aa0

Hash algo: sha1

Hash value: c336f63fd6f4e82d21439ca2843a99eea47f03bb

Verifying Hash Integrity ... crc32+ sha1+ OK

Booting using the fdt blob at 0x7a40b53c

Loading Kernel Image ... OK

OK

Loading Device Tree to 71ffa000, end 71fff7f5 ... OK

Starting kernel ...

kernel – v4.4.2

为了使Kindle4能跑brillo-m10-dev系统，kernel版本当然是使用v4.4了。相关的commit为：

commit 96cb1584b08c9a74a7cce6805354d4515c2131ae

Author: Greg Kroah-Hartman

Date: Wed Feb 17 12:31:25 2016 -0800

Linux 4.4.2

目前能够正常工作的设备有：

1. uart1 – 输出kernel log，用于kernel调试

diff --git a/drivers/clk/imx/clk.c b/drivers/clk/imx/clk.c

index a634b11..9755a46 100644

--- a/drivers/clk/imx/clk.c

+++ b/drivers/clk/imx/clk.c

@@ -101,12 +101,14 @@ void __init imx_register_uart_clocks(struct clk ** const clks[])

static int __init imx_clk_disable_uart(void)

{

+#if 0

if (imx_keep_uart_clocks && imx_uart_clocks) {

int i;

for (i = 0; imx_uart_clocks[i]; i++)

clk_disable_unprepare(*imx_uart_clocks[i]);

}

+#endif

return 0;

}

不能disable uart时钟，否则会死机。why?

2. esdhc3 – 读写eMMC

diff --git a/drivers/mmc/host/sdhci-esdhc-imx.c b/drivers/mmc/host/sdhci-esdhc-imx.c

index 1f1582f..114dcd2 100644

--- a/drivers/mmc/host/sdhci-esdhc-imx.c

+++ b/drivers/mmc/host/sdhci-esdhc-imx.c

@@ -1267,7 +1267,7 @@ static int sdhci_esdhc_runtime_suspend(struct device *dev)

ret = sdhci_runtime_suspend_host(host);

if (!sdhci_sdio_irq_enabled(host)) {

- clk_disable_unprepare(imx_data->clk_per);

+// clk_disable_unprepare(imx_data->clk_per);

clk_disable_unprepare(imx_data->clk_ipg);

}

clk_disable_unprepare(imx_data->clk_ahb);

@@ -1282,7 +1282,7 @@ static int sdhci_esdhc_runtime_resume(struct device *dev)

struct pltfm_imx_data *imx_data = pltfm_host->priv;

if (!sdhci_sdio_irq_enabled(host)) {

- clk_prepare_enable(imx_data->clk_per);

+// clk_prepare_enable(imx_data->clk_per);

clk_prepare_enable(imx_data->clk_ipg);

}

clk_prepare_enable(imx_data->clk_ahb);

在runtime suspend的时候不能disable per(外设时钟)。why?

USB 目前还存在问题，不能正常工作。

相关的编译脚本如下：

#! /bin/bash

TP="`pwd`/../tools/arm-eabi-4.6"

if [ ! -f .config ] ; then

CROSS_COMPILE=${TP}/bin/arm-eabi- ARCH=arm make imx_v6_v7_defconfig

fi

CROSS_COMPILE=${TP}/bin/arm-eabi- ARCH=arm make $@

相关的参考文档：

http://www.devicetree.org/Main_Page