CONFIG_BCH_CONST_PARAMS should be unset

[Andreas Oberritter]

Quoting lib/bch.c:

 * Option CONFIG_BCH_CONST_PARAMS can be used to force fixed values of
 * parameters m and t; thus allowing extra compiler optimizations and providing
 * better (up to 2x) encoding performance. Using this option makes sense when
 * (m,t) are fixed and known in advance, e.g. when using BCH error correction
 * on a particular NAND flash device.

Ubuntu's kernel targets generic hardware, so using this option is not a good idea.

As a result of this option being enabled, nandsim's option "bch" is unusable:

[34200.137521] nand: 128 MiB, SLC, erase size: 128 KiB, page size: 2048, OOB size: 64
[34200.137522] [nandsim] using 8-bit/512 bytes BCH ECC
[34200.137524] bch encoder/decoder was configured to support parameters m=14, t=4 only!

---

Ubuntu 18.04.1 LTS, linux-image-4.15.0-34-generic: 4.15.0-34.37 (amd64)

[Seth Forshee (sforshee)]

This option is selected as a result of having CONFIG_MTD_DOCG3. This seems to be very old hardware which only had experimental support, so I doubt there's any harm in disabling it. I agree that CONFIG_BCH_CONST_PARAMS looks to only make sense when the hardware is known. It seems it should be safe to disable these options.