[U-Boot] U-Boot as a next bootloader in a chain - reading the kernel boot args provided by the previous stage bootlader?

[Wojciech Zabolotny]

2015-11-16 11:52 GMT+01:00 Albert ARIBAUD <albert.u.boot at aribaud.net>:
> Hello Wojciech,
>
> On Mon, 16 Nov 2015 10:42:50 +0100, Wojciech Zabolotny
> <wzab01 at gmail.com> wrote:
>> Hi,
>>
>> I need to use U-Boot (or barebox) as a bootloader in a Raspberry Pi
>> based system to extend booting flexibility.
>> The problem however is that certain kernel boot arguments are prepared
>> by the previous stage bootloader (start.elf)
>> basing on the properties of the individual board.
>> For example in one of the boards I use, the kernel command line when a
>> standard kernel is booted, looks as follows (MAC address and serial
>> number are partially masked for privacy):
>>
>> dma.dmachans=0x7f35 bcm2708_fb.fbwidth=720 bcm2708_fb.fbheight=480
>> bcm2708.boardrev=0xd bcm2708.serial=0x6f15XXXX
>> smsc95xx.macaddr=B8:27:EB:XX:XX:XX bcm2708_fb.fbswap=1
>> sdhci-bcm2708.emmc_clock_freq=250000000 vc_mem.mem_base=0x1ec00000
>> vc_mem.mem_size=0x20000000  console=ttyAMA0 root=/dev/mmcblk0p2
>> rootwait
>>
>> Only the "console=ttyAMA0 root=/dev/mmcblk0p2 rootwait" is provided by
>> the user (in the cmdline.txt file). The rest is generated by the
>> start.elf.
>>
>> Of course when I boot the u-boot.bin instead of zImage, the same
>> parameters are passed to it, but the U-Boot is not able to read them
>> and to pass them to the finally booted kernel.
>> As U-Boot shares a lot of code with the Linux kernel it should be
>> possible to add necessary functions.
>> It could be useful in all applications where U-Boot is used as an
>> additional stage in the boot chain e.g., to add new booting
>> functionalities (booting from the network, booting from the flash disk
>> etc.).
>>
>> I have found a nice description, how the paremeters are passed in ARM
>> architecture:
>> http://www.simtec.co.uk/products/SWLINUX/files/booting%5Farticle.html
>> but of course the solution should be probably portable (or implemented
>> for each platform independently with unified API).
>
> Not sure what kind of answer you're asking for here. Do you want to
> know if what you're suggesting is feasible? Are you looking for someone
> to implement it? Are you going to implement it yourself but asking for
> feedback?
>
>> --
>
> (aside: if the above should be a signature delimiter, then it lacks a
> space after the dashes)
>
> Amicalement,
> --
> Albert.

Dear Albert,

Yes the first question is if this feature is feasible.

If yes, then I'd like to propose such functionality as a possible improvement.
I think that may be more people interested in such a feature.

I'll appreciate any sugestions/pointers regarding the possible implementation.

Probably I can try to implement it. Of course if there are other
interested users
who can do it, I'll be definitely happy to discuss that with them.

Regards,

-- 
Wojciech M. Zabołotny
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