I write ebuild for shasta kernel module (driver for Promise ST EX163x0/EX83x0 SATA RAID Controllers). It works fine for me on AMD64 with ST EX16350 (16 disks: RAID50: 3.5TB: BIOS v2.9.0.19).
Created attachment 95126 [details] sys-block/shasta-2.9.0.10-r1.ebuild
Created attachment 95127 [details, diff] files/shasta-2.9.0.10-x86_64.patch I do not use this patch for me. Changes which it make here: http://forums.gentoo.org/viewtopic-t-434288.html
Don't use unzip in src_unpack, no need to do such weird stuff. Just src_unpack() { unpack ${A} cd "${S}" epatch "${FILESDIR}"/shasta-2.9.0.10-x86_64.patch } will work fine. Also, remove virtual/modutils and virtual/linux-sources from dependencies, the eclasses already take care of this properly.
Created attachment 95166 [details] sys-block/shasta-2.9.0.10.ebuild I keep mkdir ${S} because zip archive do not contain directory.
Driver were build in to the linux kernel 2.6.20 and later.