[U-Boot] [SPL mode] Question

[Lukasz Majewski]

Hi Andreas,

> Dear Lukasz Majewski,
> 
> On 15.11.2012 16:51, Lukasz Majewski wrote:
> > Hi Stefano,
> > 
> > I've got some questions about Falcon mode and spl export command.
> > 
> > I've looked into the ./common/cmd_spl.c at master branch
> > SHA1: 59852d03867108217fe88e3bfc3e1e9cedfe63c5
> > 
> > Correct me if I'm wrong (or I've overlooked something). 
> > It looks that, this file version is a very early version. 
> 
> It is.
> 
> > After reading "Falcon" mode README - I'd expect, that "spl export"
> > will write either ATAGS or FDT to NAND (or any other memory).
> > For this file it doesn't do that. Am I missing some additional
> > patches?
> 
> No, the 'spl export' does not write to a storage media at all, the
> 'spl export' command is intended to save the prepared information in
> RAM. This information must then be transferred to a final destination
> where the SPL will load it. The destination is defined at compile time
> (CONFIG_CMD_SPL_NAND_OFS for NAND).
> 
> > Since you stated, that Falcon mode is only (now) supported on NAND
> > memory, I'd like to ask if it is acceptable to extend cmd_spl.c to
> > write ATAGS/FDT image to eMMC or (better) to partition formatted as
> > EXT4 of FAT?
> 
> So far only NAND is implemented, if you plan to implement another mode
> you need to extend the SPL by some mechanism to get the required data
> ('configuration BLOB' either ATAGS or FDT) and kernel from that media.
> The 'configuration BLOB' generated by the 'spl export' command should
> then be saved by other existing u-boot commands to its final
> destination. I think the spl command do not need to know about the
> storage media used. I personally think a 'spl export ..; nand write
> ...;' is fine, for more convenience this could also be scripted. In a
> perfect world you will do this only once, but the complexity of spl
> command will be carried always.
> 
> > I can imagine a following scenario:
> > 
> > 1. Use u-boot to generate ATAGS (from bootcmd args defined for board
> > or cmd line parameters) or FDT blob with "spl export". Store it on a
> > partition or eMMC.
> 
> Well, the FDT blob will not be generated by the 'spl export' (or did I
> get this wrong?). You will need a FDT blob to generate the stuff that
> is handed to the kernel. In fact the existing FDT is encapsulated by
> some header, isn't it that way?
> 
> > 2. Use SPL (second stage bootloader) to parse this blob, place
> > ATAGS or FDT accordingly, read uImage and pass execution to it.
> 
> SPL should not parse but copy the prepared data to RAM and branch the
> kernel.
> 
> Best regards
> 
> Andreas Bießmann

Thanks for clarification. This is what I was missing.

-- 
Best regards,

Lukasz Majewski

Samsung Poland R&D Center | Linux Platform Group