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>

1 files changed, 15 insertions, 0 deletions

diff --git a/Documentation/spi/spi-summary b/Documentation/spi/spi-summary
index f72e0d1e0da8..dcaad476789c 100644
--- 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)