Oops, apparently no-one I cc'd at intel actually bothered to check this
patch for the isci driver:
commit 
e73823f7a2c921dcf068d34ea03bd682498d9e42
Author: James Bottomley <JBottomley@Parallels.com>
Date:   Tue May 7 15:38:18 2013 -0700
    [SCSI] libsas: implement > 16 byte CDB support
sci_swab32_cpy needs multiples of four, so for commands that aren't that, it's
rounding the wrong way.  fix by doing (len+3)/4 instead of len/4.
Reported-by: Tony Luck <tony.luck@intel.com>
Tested-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>
 
        cmd_iu->_r_c = 0;
 
        sci_swab32_cpy(&cmd_iu->cdb, task->ssp_task.cmd->cmnd,
-                      task->ssp_task.cmd->cmd_len / sizeof(u32));
+                      (task->ssp_task.cmd->cmd_len+3) / sizeof(u32));
 }
 
 static void sci_task_request_build_ssp_task_iu(struct isci_request *ireq)