mtd: nand: document nand_chip.oob_poi

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@intel.com>

include/linux/mtd/nand.h

@@ -431,7 +431,8 @@ struct nand_buffers {
  * @chip_delay:		[BOARDSPECIFIC] chip dependent delay for transferring
  *			data from array to read regs (tR).
  * @state:		[INTERN] the current state of the NAND device
- * @oob_poi:		poison value buffer
+ * @oob_poi:		"poison value buffer," used for laying out OOB data
+ *			before writing
  * @page_shift:		[INTERN] number of address bits in a page (column
  *			address bits).
  * @phys_erase_shift:	[INTERN] number of address bits in a physical eraseblock