diff --git a/Documentation/i2c/slave-interface.rst b/Documentation/i2c/slave-interface.rst
index 58fb143baee4..3f0d320bc80a 100644
--- a/Documentation/i2c/slave-interface.rst
+++ b/Documentation/i2c/slave-interface.rst
@@ -72,12 +72,15 @@ Event types:
 
   'val': unused
 
-  'ret': always 0
+  'ret': 0 if the backend is ready, otherwise some errno
 
 Another I2C master wants to write data to us. This event should be sent once
 our own address and the write bit was detected. The data did not arrive yet, so
-there is nothing to process or return. Wakeup or initialization probably needs
-to be done, though.
+there is nothing to process or return. After returning, the bus driver must
+always ack the address phase. If 'ret' is zero, backend initialization or
+wakeup is done and further data may be received. If 'ret' is an errno, the bus
+driver should nack all incoming bytes until the next stop condition to enforce
+a retry of the transmission.
 
 * I2C_SLAVE_READ_REQUESTED (mandatory)