[U-Boot-Users] MTD Concat support

[Vlad Lungu]

Luigi 'Comio' Mantellini wrote:
> Hi Guys,
>
> I'm a question regarding the MTD Concat support in U-BOOT.
> My system has 2 Flash (x16MB) driven by 2 different Chipselects. The
> memory layout is the following:
>
> [0xbe000000 -> 0xbeffffff ] Flash#0 CS#0
> [0xbf000000 -> 0xbfffffff ] Flash#1 CS#1
>
> I would link to create a JFFS2 partition across the two flash banks with size about 28M. In other hands I should meet the following partition layout:
>
> [0xbe000000 -> 0xbfc00000 ] JFFS2 root 
> [0xbfc00000 -> 0xbfe00000 ] U-BOOT code
> [0xbfe00000 -> 0xbfffffff ] DATA
>
>   
So you have 16+12Mo then u-boot then 2 Mo left. 
> Into the JFFS2 filesystem there are the Kernel images and a lot of spare datas.
>   
That's a rather big JFFS filesystem. Do you plan booting from it? Isn't 
it rather slow? It would take a few seconds (5-10) to
scan the FS on this under U-Boot. I would recommend two strategies here:
-put the uImage directly in the NOR flash. Maybe in those 2 Mo at the 
end or somewhere else. Update it from Linux
or if you screw up, from the network.
-create a smaller partition (like 4Mo) and keep two kernels there, main 
and spare. Mount it under /boot in Linux.
Boot from there. Use the rest of the available space as root with the 
MTD concat driver but don't touch it from U-Boot.
Will boot much faster than from a 28Mo partition, you can use *summary* 
information on root (not supported in U-Boot)
for faster mount in Linux, more versatile than uImage in NOR (you can 
have 1 or more spares depending on kernel sizes and partition size).
> How I can say to U-boot to consider the two flashes as a single space of
> memory (in order to place a big JFFS2 filesystem)? In Linux I can
> achieve this using the MTD Concat driver but I don't understand How I
> can do in U-boot.
>   
What you are asking could be already possible, or require just a few 
modifications, but you have to ask yourself: do I really HAVE to do this?

Regards,
Vlad