[U-Boot] using initrd with U-boot on the imx28evk

[Bill <bsousan@techsi.com>]

I'm using U-boot version:  U-Boot 2012.07

Through googling, I've come across several variations of using a 
ramdisk.  So I selected some things that looked good.  So basically, I 
am building  a rootfs as a ramdisk by:

    dd if=/dev/zero of=./myinitrd.img bs=1M count=35
    mke2fs -m 1 ./myinitrd.img
    mkdir ./myinitrd
    mount -t ext2 ./myinitrd.img ./myinitrd -o loop
    cp -r rootfs/*  ./myinitrd/.
    umount ./myinitrd/
    gzip ./myinitrd.img
    rm -rf myinitrd


Then I use the u-boot tool to prepare it for use with u-boot by:
      u-boot-imx/tools/mkimage  -n 'MyRamDisk' -A arm -O linux -T 
ramdisk -C none -d ./myinitrd.img.gz rootfs-initrd

I place both both my uImage and rootfs-initrd on a USB stick and insert 
it into the imx28evk and enter u-boot command line.  I then do:

    usb start
    fatload usb 0 0x42000000 uimage
    fatload usb 0 0x43000000 rootfs-initrd
    setenv bootargs console=ttyAM0,115200n8 debug root=/dev/ram rw  
ip=dhcp  fec_mac=
    bootm 0x42000000 0x43000000


u-boot then starts booting with:

## Booting kernel from Legacy Image at 42000000 ...
    Image Name:   Linux-2.6.35.3-571-gcca29a0-g45b
    Created:      2012-09-08  22:31:46 UTC
    Image Type:   ARM Linux Kernel Image (uncompressed)
    Data Size:    2582304 Bytes = 2.5 MiB
    Load Address: 40008000
    Entry Point:  40008000
    Verifying Checksum ... OK
## Loading init Ramdisk from Legacy Image at 43000000 ...
    Image Name:   MyRamDisk
    Created:      2012-09-12  20:51:35 UTC
    Image Type:   ARM Linux RAMDisk Image (uncompressed)
    Data Size:    37774 Bytes = 36.9 KiB
    Load Address: 00000000
    Entry Point:  00000000
    Verifying Checksum ... OK
    Loading Kernel Image ... OK
OK

Starting kernel ...

Uncompressing Linux... done, booting the kernel.
Linux version 2.6.35.3-571-gcca29a0-g45b53d0-dirty (blsousan at ubuntu) 
(gcc version 4.4.4 (4.4.4_09.06.2010) ) #13 PREEMPT Sat Sep 8 14:06:34 
PDT 2012
CPU: ARM926EJ-S [41069265] revision 5 (ARMv5TEJ), cr=00053177
CPU: VIVT data cache, VIVT instruction cache
Machine: Freescale MX28EVK board
....
....
....

The kernel starts to boot, I get all the kernel output, and at the end 
it does not find the rootfs.  I get:

...
...
...

List of all partitions:
b300         3872256 mmcblk0 driver: mmcblk
   b301            1024 mmcblk0p1
0800          503808 sda driver: sd
   0801          503792 sda1
No filesystem could mount root, tried:  ext3 ext2 vfat msdos iso9660
Kernel panic - not syncing: VFS: Unable to mount root fs on 
unknown-block(1,0)
Backtrace:


I not sure how the kernel knows where the ramdisk lives in memory ( 
0x43000000) where the the uboot put it ?


Thanks,
Bill








On 9/12/2012 5:29 PM, Marek Vasut wrote:
> Dear Bill,
>
>> Has anyone used U-boot on the imx28evk with initrd to setup a small
>> rootfs in RAM?  I need the ability to do have a small temp rootfs to
>> assist in mounting a full rootfs from a USB for field upgrade purposes.
> Yes, it's a linux thingie though. What's the problem? What version of uboot do
> you use?
>
>> Thanks,
>> Bill
> Best regards,
> Marek Vasut

-- 
William (Bill) L. Sousan, Ph.D.
(w) 402.331.4977 ext. 4002
bsousan at techsi.com
Technical Support Inc.
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