Just to keep you informed: I can now erase my n25q512 (JEDEC 20ba20) from Linux. To do this, I applied the SPI-NOR patches from http://git.infradead.org/l2-mtd.git/shortlog/refs/heads/spinor (from tag 3.15-rc1 to HEAD). On top of it, I applied http://patchwork.ozlabs.org/patch/341355/