[U-Boot] What shall u-boot do before passing 'root=/dev/ram0' to kernel?

[mike xu]

Hi Wolfgang,

Thanks for your reply. Maybe I need try to generate the big endian
format ramdisk...
Any ideas of generating big endian format ramdisk on a intel PC?

Best regards,
Mike

On Fri, Dec 19, 2008 at 5:53 AM, Wolfgang Denk <wd at denx.de> wrote:
> Dear "mike xu",
>
> In message <7103aeea0812181017j19966d84y22528f8728d5a1c at mail.gmail.com> you wrote:
>>
>> Do you know that what u-boot shall do after passing 'root=/dev/ram0'
>> to kernel? How kernel locates /dev/ram0?
>
> U-Boot starts the Linux kernel.
>
> How the Linux  kernel  receives  it's  parameters  is  more  a  Linux
> specific  question  -  so  far, MIPS failed to com up with a standard
> solution for this problem (at least I don't know one).
>
> You might even go ahead and make yourselkf a name in the community by
> implementing device tree awarenes for MIPS ;-)
>
>> I want to use one ramdisk as my rootfs, but the kernel failed to mount
>> the ramdisk, I set the u-boot parameter as below.
>>  setenv bootargs console=ttyS0,115200 root=/dev/ram0 ro mem=128M
>>
>> kernel reports errors:
>>   No filesystem could mount root, tried:  ext2 cramfs squashfs romfs
>>   Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(1,0)
>
> See previous message.
>
>> root=/dev/ram1 also failed... What's the difference between /dev/ram0
>> and /dev/ram1?
>
> It's the same as between /dev/sda and /dev/sdb - they are differend
> devices.
>
>> And are there any requirement for the ramdisk image? Such as
>> little/big endian, block size?
>
> Yes, of course there are such requirements - they have to match what
> your kernel expects.
>
> Best regards,
>
> Wolfgang Denk
>
> --
> DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
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>