spi: document the transfer_one spi_master callback

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Mark Brown <broonie@linaro.org>

diff --git a/Documentation/spi/spi-summary b/Documentation/spi/spi-summary
index f72e0d1e0da852ac3e89e97f8bd0c22055d66608..dcaad476789c0b6914ebc0cc7a24d73cfc2ee6e3 100644 (file)
--- a/Documentation/spi/spi-summary
+++ b/Documentation/spi/spi-summary
@@ -545,6 +545,21 @@ SPI MASTER METHODS
        spi_finalize_current_message() so the subsystem can issue the next
        transfer. This may sleep.
 
+    master->transfer_one(struct spi_master *master, struct spi_device *spi,
+                        struct spi_transfer *transfer)
+       The subsystem calls the driver to transfer a single transfer while
+       queuing transfers that arrive in the meantime. When the driver is
+       finished with this transfer, it must call
+       spi_finalize_current_transfer() so the subsystem can issue the next
+       transfer. This may sleep. Note: transfer_one and transfer_one_message
+       are mutually exclusive; when both are set, the generic subsystem does
+       not call your transfer_one callback.
+
+       Return values:
+       negative errno: error
+       0: transfer is finished
+       1: transfer is still in progress
+
     DEPRECATED METHODS
 
     master->transfer(struct spi_device *spi, struct spi_message *message)