Launching the latest Linux kernel on Intel Edison

For World ArduinoD15 Day, I have prepared material on the configuration and launch of the latest Linux kernel on the Intel Edison (Arduino Edition) board.

Earlier, I wrote about how to ensure that the vanilla core is loaded on the Intel Galileo board, but now it’s the turn for Intel Edison.


To date, there is no serial port driver in vanilla kernels, which practically makes working with the board impossible. Today, Greg KH, the tty subsystem maintainer, has approved the changes that bring Intel Edison High Speed ​​UART support to the kernel. In reality, in the main branch, changes will appear only in version v4.1-rc1.

So let's get started. I want to immediately note that I will not re-describe some of the actions described in the article Launching the Vanilla Core on Intel Galileo. I also assume that you are using stock firmware based on Yocto.

Preparing the kernel and file system

First of all, we need a kernel that can be easily accessed from the linux-next repository of the tty subsystem repository (we will need a branch tty-next) :

mkdir ~/devel
cd ~/devel
git clone git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
cd ~/devel/linux-next

You need to make a few minimal changes to the default configuration, namely the arch / x86 / configs / i386_defconfig file . If for some reason you do not want to touch this file, we can easily copy it using the command cp arch/x86/configs/{i386,eds}_defconfig, and in this case use eds_defconfig where i386_defconfig is mentioned in the article .

So it was (delete lines from the file):

CONFIG_DRM_I915 = y

Now (add lines to the file):

# CONFIG_DRM_I915 is not set
CONFIG_BACKLIGHT_LCD_SUPPORT = y
CONFIG_USB_XHCI_HCD = y
CONFIG_USB_DWC3 = y
CONFIG_USB_DWC3_GADGET = y
CONFIG_GPIOLIB = y
CONFIG_GPIO_INTEL_MID = y
CONFIG_INTEL_MID_WATCHDOG = y
CONFIG_X86_EXTENDED_PLATFORM = y
CONFIG_X86_INTEL_MID = y
CONFIG_EFI_STUB = y
CONFIG_EARLY_PRINTK_EFI = y
CONFIG_HSU_DMA = y
CONFIG_HSU_DMA_PCI = y
CONFIG_SERIAL_8250_DMA = y
CONFIG_SERIAL_8250_PCI = y

This configuration will immediately enable USB, watchdog, GPIO, HSU drivers.

We collect the received:

make i386_defconfig
make -j4

The result is the file arch / x86 / boot / bzImage .

The process of preparing the image of the file system is no different from the one described above, with the exception of the output device, which for Intel Edison will be / dev / ttyS2 , and accordingly it must be specified in the Buildroot configuration parameters:

BR2_TARGET_GENERIC_GETTY_PORT = "ttyS2"

As a result of the assembly, we get the file output / images / rootfs.cpio.bz2 .

Copy results to eMMC

The files ~ / devel / linux / arch / x86 / boot / bzImage and
~ / devel / buildroot / output / images / rootfs.cpio.bz2 obtained during the assembly must be copied to our board under the names vmlinuz.efi and initrd, respectively.

We launch the board on the stock firmware by first switching it to the device mode via USB and connecting the cable to the computer on which we were assembling. After starting the board, the computer will find the USB drive device. This is what we need. We copy our files directly to the root of the mapped drive.

Configuring the U-Boot bootloader

The most interesting part of the story is the magic lines that we need to write to the U-Boot configuration. This is what we need to do.

1. Download the board to the U-Boot command line by pressing any key.
2. Add a few environment variables so that the following happens:
   

     boot_edsboot=zboot 0x100000 0 0x3000000 0x800000
     bootargs_edsboot=console=tty1 console=ttyS2,115200n8 rootfstype=ramfs rw
     bootcmd_edsboot=setenv bootargs ${bootargs_edsboot}; run load_edsboot; run boot_edsboot
     load_edsboot=load mmc 0:9 0x100000 vmlinuz.efi; load mmc 0:9 0x3000000 initrd
   

   
   This is done using the command setenv(detailed examples can be found here ).
3. Save our changes without ruining the existing ones:
   

     setenv bootcmd_orig ${bootcmd}
     setenv bootcmd ${bootcmd_edsboot}
     saveenv
   

Now you can load the board, for example, with this command:

run bootcmd

or by pressing the reset button.

Accordingly, you can always return to the original configuration by running:

run bootcmd_orig

And that is all!