[U-Boot] Linux boot and list loading feature

[Aneesh V]

Hi Simon,

On Monday 01 August 2011 07:43 PM, Simon Schwarz wrote:
> Hi Aneesh,
>
> On 08/01/2011 02:56 PM, Aneesh V wrote:
>> Hi Simon,
>>
>> On Monday 01 August 2011 04:50 PM, Simon Schwarz wrote:
>>> Hi Aneesh,
>>>
>>> I am working on the OS booting right now and have a bigger change of
>>> your code in spl.c in mind.
>>>
>>> Hope you can say one or two words what you think about it.
>>>
>>> THE PROBLEM
>>> For the direct OS boot and in some other situations - env image e.g., I
>>> have to load more than one image in SPL.
>>>
>>> This can be done by hardcoding these cases and use #ifdef or ifs to
>>> switch between them. Or I can implement a general image loading with
>>> lists.
>>> (This was discussed here:
>>> http://article.gmane.org/gmane.comp.boot-loaders.u-boot/102345)
>>
>> At the outset, wonder why we can not use the default bootargs string in
>> the kernel image instead of passing it from the bootloader. For direct
>> kernel boot from SPL, that looks like the best option for me. Then we
>> will not need all this. Am I missing something?
>>
>  From the documentation it is mandatory for ARM to pass ATAGS (or FDT I
> assume): http://www.arm.linux.org.uk/developer/booting.php
>
> So I think your solution would work - but IMHO would be too simple.
>
> The beauty is that we can save the config of ATAGS/FDT directly in
> u-boot and pass this image at the next boot to the SPL. This means we
> can boot the exact same configuration with the SPL as with standard
> u-boot - without recompiling the kernel. Trade-off: a more complex SPL.

If my suggestion works I would still prefer that. If you want better
configurability you can always use u-boot! Direct kernel boot from SPL
is likely to be used in production systems for improved boot-time,
where it should be OK to hard-code the boot-args. Using u-boot seems to
be a better option if changing bootargs frequently is a requirement.

Please note that any scheme that you comes up with should also work for
FAT boot from SD/MMC card, which means you need to have a way of
converting your ATAGS list into a file, reading it and so on. A lot of
trouble without much value-add in my opinion(assuming that hard-coded
bootargs works).

In the worst case I would prefer hard-coding bootargs in SPL in a
config flag and using it to build the list in SPL.

I would love to hear others' views on this.

best regards,
Aneesh