[U-Boot] [PATCH v2 6/8] omap_gpmc: BCH8 support (ELM based)

[Peter Korsgaard]

>>>>> "Andreas" == Andreas Bießmann <andreas.devel at googlemail.com> writes:

Hi,

 >> Please note that these patches are AM33XX-specific (as we are using
 >> ELM that, I think, just isn't available on OMAP3) so we use OOB
 >> layout that is compatible with AM33xx ROM boot code.

 Andreas> You are right, ELM is not available in OMAP3 devices. It seems
 Andreas> the ROM loader of these devices only support the 1-Bit
 Andreas> Hamming, but is also different to the OOB layout used for the
 Andreas> SW 1-bit hamming provided by the Kernel.  So we get here a lot
 Andreas> of different OOB layouts ... I wonder if we can stick to
 Andreas> e.g. the generic SW BCH layout (of linux kernel) for all but
 Andreas> the ROM partition (where the SPL is placed). So the SPL need
 Andreas> to know just one mechanism but software modifying that place
 Andreas> needs to know about the 'special' ROM layout.

No, please not. Having more than 1 OOB layout on the same NAND device
leads to all kind of complications. There has also been kernel patches
posted for the ELM, so IMHO the only sane option for am33xx is BCH8
everywhere (with the ROM layout).


 >> It's likely that this layout
 >> doesn't match with the current kernel layout as RBL uses strange 14th
 >> byte for BCH8 while only 13 bytes are needed. 

 Andreas> Sorry, what does RBL mean in that context?

The ROM boot loader, E.G. the part loading the spl.


 >> Actually, the only assumption the code does about the OOB layout is that
 >> ECC code occupies continuous area in the OOB.

 Andreas> Well, but you have defined that for example it is written in
 Andreas> big endian.

 Andreas> I'm currently working on a omap3 enabled device that requires
 Andreas> 4-bit ECC for all but the first block. And I'm searching for a
 Andreas> clean solution that would be accepted mainline.  I think it
 Andreas> would be best to have the same OOB layout for the whole device
 Andreas> but the SPL space (cause that needs to be read by ROM). The
 Andreas> layout should be chosen at compile time of the SPL.  What do
 Andreas> you think about?

So the only reason to not have the same OOB layout everywhere is because
of ROM restrictions and that 1bit ECC isn't good enough anymore?
E.G. you actually would have prefered to use the ROM layout if it would
have used something better like the am33xx ROM does.

-- 
Bye, Peter Korsgaard