From: Jeroen Hofstee [mailto:jeroen@myspectrum.nl]
[...]
The gpmc will fail in hw ecc mode when trying to do subpage reads. Pekon any suggestion for the elm mode, or should this bit just be cleared unconditionally?
There are two reasons for not supporting sub-page feature in OMAP platforms:
(1) ELM h/w engine has limitation that it can support ecc-corrections only in junks of 512Bytes. Now some flash devices (like page-size=4K) have sub-page = 4k/4 = 1k. Thus, it becomes trivial (though not impossible) to support sub-page. Hence, for now sub-page feature has been marked as 'un-supported' for OMAP.
(2) Also, we found that sub-page feature was not giving much benefit, except improving data-packing density on given NAND to some extent. Like in UBIFS, having sub-page feature packs 'erase-header' and volume-id-header' into single page, thereby saving 1 page for every erase-block. Memory Saved = (1x page-size)/ block-size = 2k / 128k = 1/64 ~ 1.5 % (raw calculations).
Hence, in summary, yes you can un-conditionally clear the sub-page read bit.
with regards, pekon