spi: Clarify transfer_one() w.r.t. spi_finalize_current_transfer()

Signed-off-by: Geert Uytterhoeven <geert+renesas@linux-m68k.org>
Signed-off-by: Mark Brown <broonie@linaro.org>

include/linux/spi/spi.h

@@ -282,10 +282,12 @@ static inline void spi_unregister_driver(struct spi_driver *sdrv)
  * @prepare_message: set up the controller to transfer a single message,
  *                   for example doing DMA mapping.  Called from threaded
  *                   context.
- * @transfer_one: transfer a single spi_transfer. When the
- *	          driver is finished with this transfer it must call
- *	          spi_finalize_current_transfer() so the subsystem can issue
- *                the next transfer
+ * @transfer_one: transfer a single spi_transfer.
+ *                  - return 0 if the transfer is finished,
+ *                  - return 1 if the transfer is still in progress. When
+ *                    the driver is finished with this transfer it must
+ *                    call spi_finalize_current_transfer() so the subsystem
+ *                    can issue the next transfer
  * @unprepare_message: undo any work done by prepare_message().
  * @cs_gpios: Array of GPIOs to use as chip select lines; one per CS
  *	number. Any individual value may be -ENOENT for CS lines that