[U-Boot] [PATCH v3 0/7] tegra: Add NAND flash support

[Thierry Reding]

* Stephen Warren wrote:
> On 04/26/2012 11:10 PM, Thierry Reding wrote:
> > * Stephen Warren wrote:
> >> On 04/26/2012 12:32 PM, Thierry Reding wrote:
> >>> The problem is that neither the format of the BCT nor that of the PT is
> >>> documented anywhere. It seems like the BCT contains a reference to where in
> >>> the flash the PT starts but I wasn't able to find out where.
> ...
> >>> As I said before, the biggest problem with updating the whole content is that
> >>> there's no documentation about either the BCT or the PT. There's cbootimage
> >>> on gitorious that has some information about the BCT, but it's incomplete.
> >>
> >> Out of curiosity, what's missing from cbootimage?
> > 
> > It's missing support for PT. That may not be necessary in a setup where we
> > initialize the NAND from Linux user space, though, so maybe it would be
> > enough.
> 
> I don't believe the Tegra boot process actually /requires/ the PT even
> exist. IIRC, the boot ROM searches for the BCT, and the BCT contains a
> pointer to the bootloader (e.g. U-Boot), so it's only at a later stage
> in the game that anything would care about the PT. As such, worrying
> about the PT (or even including it) may be pointless.

After digging into this some more, I get the same impression. PT seems
entirely optional. Information about the bootloader seems to be stored within
the BCT.

> I believe that TrimSlice's firmware recovery SD card images are created
> solely using cbootimage, and hence most likely have no PT, although
> obviously no additional partitions/file-systems on the media.

It looks like cbootimage does have support for generating the bootloader
bits, so maybe I can get this to work.

> Perhaps you could define some hard-coded "MTD" partitions (e.g. the
> first 1MB and the rest), where the first 1MB contains BCT + U-Boot and
> the rest contains a regular MBR or GPT partition table. I /think/ there
> may even be a kernel command-line option to define the MTD partition layout?
> 
> Or, you could probably even get away with using a GPT for the entire
> NAND by placing just the secondary GPT at the end of the NAND, putting
> the BCT+U-Boot right at the start, and defining a GPT partition to
> protect/cover BCT+U-Boot. I vaguely recall trying this on some Tegra
> device, but I may be wrong.

I didn't even know that you could put an MBR or GPT onto NAND. I was under
the impression that the only way to partition flash was via MTD partitions.
I'll have to see if I can make such a setup work.

Thierry
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