Hi Robert.
I set the bootargs variable to: root=\dev\ram (I used: set bootargs root=/dev/ram) But when I'm trying to start the Linux with the
bootm 81000000 81FFFFC0
the Linux can't find the ramdisk. It write out:
Initrd not found or empty - disabling initrd
Do you see U-Boot detecting and loading the ram disk image once you invoke your bootm command above? eg:
## Loading RAMDisk Image at 00500000 ... Image Name: uboot ext2 ramdisk rootfs Created: 2009-06-15 14:39:13 UTC Image Type: M68K Linux RAMDisk Image (gzip compressed) Data Size: 5219290 Bytes = 5 MB Load Address: 00000000 Entry Point: 00000000 Verifying Checksum ... OK Loading Ramdisk to 4fa79000, end 4ff733da ... OK
I believe that for U-Boot to pass the ram disk image information to the kernel, it needs to be able to detect the ram disk image in the first place. You can use U-Boot's mkimage utility to add a header onto your ram disk image.
But when I set its address into the bootargs (so the bootargs: root=/dev/ram rd_start=0x82000000 rd_size=0x191160), it works well; it successfully find the image, and can mount it.
This is because you're explicitly telling the kernel where to find the ram disk image in memory. Take a look at drivers/block/brd.c in the kernel src.
How does the U-Boot pass the ramdisk information? It sets some kind of environment variables in the bootm.c. But it doesn't work for me. Why? (I could use the bootargs solution in this case, but I'm afraid, it can't pass other arguments too, like ethernet address, etc.)
This is arch specific in U-Boot but I'd also check that your MIPS kernel has support for a) correctly parsing the U-Boot environment provided to it and b) providing the required data to other parts of the kernel for utilisation of the ram disk, eg initrd_start / initrd_end as an example.
If you're struggling to pass other args to the kernel then it sounds like there is more of a fundamental issue somewhere, though. Maybe just double check Documentation/kernel-parameters.txt to make sure you're passing syntax in a form that the kernel will recognise?
Hope that helps.
Cheers, -- Matt