[U-Boot] [PATCH 01/13] mxc nand: Merge mtd and spl register definitions

[Stefano Babic]

On 14/08/2012 12:15, Benoît Thébaudeau wrote:
> Then, I don't know what to do with these patches.

I see two main points in your patches. You cleanup mxc-nand code and add
support for i.MX5. This is one topic, and it can go on.

> 
> Note that this is not a new implementation, but only an enhancement of the
> existing one. But I understand your point.

;-)

> 
> I don't see any i.MX board using the general SPL for NAND.

At least the MX28, and using nand_spl with MX28 was rejected for the
same reason when it was pushed. Then it was switched to SPL.

But surely it should be better to have more examples - I am working to
get a MX35 booting from external SD, and using the SPL.

> So we can't say that
> it's usable with the current mtd mxc_nand driver in its current state. Moreover,
> with the general SPL, I'd be very concerned as to the code size of mxc_nand (the
> target size of the whole SPL code is only 2 kiB for current i.MX users of
> nand_spl).

Mainly because the restriction came from the original implementation,
that was for PowerPC 4xx with only a small buffer (NFC buffer) to copy
data from NAND.

We have currently only two boards supporting this mechanismus, using
MX25 (karo tx25) and MX31. Both MX25 and MX31 have an internal RAM
(128KB) that is is suitable for installing the SPL. Note that TI SOCs
have less RAM available, and they support SPL.

IMHO the fact that only two IMX boards are using this mechanism
(nand_spl) is also due the fact that is not very flexible. And moving to
SPL we are not fixed to boot exclusively from NAND,

> 
> IMHO, we could improve and fix the nand_spl code while it's still there and
> used.

However, as you say, if the code is still available, this makes people
think that is the correct way to do and we will have two distinct
implementation (the old one and the new one), both to be supported.

Not to forget that the SPL is thought to work with different SOCs, even
if currently it is mainly used by TI, and with different media storage.
All features taht we discussed previously in the ML if we had to add
them to nand_spl, before the new implementation was pushed.

> This does not prevent from moving to the general SPL once ready for
> mxc_nand. These are two different topics.

The fact is it will be nice if also the two supported boards will move
to SPL. Of couse, we cannot break these boards, but a move will be more
difficult if we increase the number of boards using nand_spl.

Best regards,
Stefano Babic

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