To debug flash-related problems, enable CONFIG_MTD_DEBUG (Device Drivers Memory Technology Devices Debugging) during kernel configuration. You can further tune the debug verbosity level to between 0 and 3.
The Linux-MTD project page www.linux-mtd.infradead.org has FAQs, various pieces of documentation, and a Linux-MTD JFFS HOWTO that provides insights into JFFS2 design. The linux-mtd mailing list is the place to discuss questions related to MTD device drivers. Look at http://lists.infradead.org/pipermail/linux-mtd/ for the mailing list archives.