diff --git a/drivers/spi/spi_context.h b/drivers/spi/spi_context.h
index 1aed41173eecc1..a5110f52de8c6c 100644
--- a/drivers/spi/spi_context.h
+++ b/drivers/spi/spi_context.h
@@ -321,6 +321,10 @@ void spi_context_buffers_setup(struct spi_context *ctx,
 		(void *)ctx->rx_buf, ctx->rx_len);
 }
 
+/*
+ * Note: dfs is the number of bytes needed to store a data frame,
+ * while len is the number of data frames sent.
+ */
 static ALWAYS_INLINE
 void spi_context_update_tx(struct spi_context *ctx, uint8_t dfs, uint32_t len)
 {
@@ -361,6 +365,10 @@ bool spi_context_tx_buf_on(struct spi_context *ctx)
 	return !!(ctx->tx_buf && ctx->tx_len);
 }
 
+/*
+ * Note: dfs is the number of bytes needed to store a data frame,
+ * while len is the number of data frames received.
+ */
 static ALWAYS_INLINE
 void spi_context_update_rx(struct spi_context *ctx, uint8_t dfs, uint32_t len)
 {
diff --git a/include/zephyr/drivers/spi.h b/include/zephyr/drivers/spi.h
index 958211e8294d03..09800a400cb069 100644
--- a/include/zephyr/drivers/spi.h
+++ b/include/zephyr/drivers/spi.h
@@ -100,10 +100,10 @@ extern "C" {
 #define SPI_WORD_SIZE_SHIFT	(5U)
 #define SPI_WORD_SIZE_MASK	(0x3FU << SPI_WORD_SIZE_SHIFT)
 /** @endcond */
-/** Get SPI word size. */
+/** Get SPI word size (data frame size) in bits. */
 #define SPI_WORD_SIZE_GET(_operation_)					\
 	(((_operation_) & SPI_WORD_SIZE_MASK) >> SPI_WORD_SIZE_SHIFT)
-/** Set SPI word size. */
+/** Set SPI word size (data frame size) in bits. */
 #define SPI_WORD_SET(_word_size_)		\
 	((_word_size_) << SPI_WORD_SIZE_SHIFT)
 /** @} */
@@ -309,7 +309,7 @@ struct spi_config {
 	 * - 0:      Master or slave.
 	 * - 1..3:   Polarity, phase and loop mode.
 	 * - 4:      LSB or MSB first.
-	 * - 5..10:  Size of a data frame in bits.
+	 * - 5..10:  Size of a data frame (word) in bits.
 	 * - 11:     Full/half duplex.
 	 * - 12:     Hold on the CS line if possible.
 	 * - 13:     Keep resource locked for the caller.
@@ -458,7 +458,7 @@ struct spi_dt_spec {
 struct spi_buf {
 	/** Valid pointer to a data buffer, or NULL otherwise */
 	void *buf;
-	/** Length of the buffer @a buf.
+	/** Length of the buffer @a buf in bytes.
 	 * If @a buf is NULL, length which as to be sent as dummy bytes (as TX
 	 * buffer) or the length of bytes that should be skipped (as RX buffer).
 	 */
@@ -471,7 +471,7 @@ struct spi_buf {
 struct spi_buf_set {
 	/** Pointer to an array of spi_buf, or NULL */
 	const struct spi_buf *buffers;
-	/** Length of the array pointed by @a buffers */
+	/** Length of the array (number of buffers) pointed by @a buffers */
 	size_t count;
 };