---

yaml
---
r: 47933
b: refs/heads/master
c: 8022456
h: refs/heads/master
i:
  47931: d34d3cf
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 0ffa0285052607513a29f529ddb5061c907fd8a6
+refs/heads/master: 802245611adea5e5877d8c5d9a20f94d8131bfdd

trunk/include/linux/spi/spi.h

@@ -163,7 +163,8 @@ static inline void spi_unregister_driver(struct spi_driver *sdrv)
  *	each slave has a chipselect signal, but it's common that not
  *	every chipselect is connected to a slave.
  * @setup: updates the device mode and clocking records used by a
- *	device's SPI controller; protocol code may call this.
+ *	device's SPI controller; protocol code may call this.  This
+ *	must fail if an unrecognized or unsupported mode is requested.
  * @transfer: adds a message to the controller's transfer queue.
  * @cleanup: frees controller-specific state
  *
@@ -305,6 +306,16 @@ extern struct spi_master *spi_busnum_to_master(u16 busnum);
  * shifting out three bytes with word size of sixteen or twenty bits;
  * the former uses two bytes per word, the latter uses four bytes.)
  *
+ * In-memory data values are always in native CPU byte order, translated
+ * from the wire byte order (big-endian except with SPI_LSB_FIRST).  So
+ * for example when bits_per_word is sixteen, buffers are 2N bytes long
+ * and hold N sixteen bit words in CPU byte order.
+ *
+ * When the word size of the SPI transfer is not a power-of-two multiple
+ * of eight bits, those in-memory words include extra bits.  In-memory
+ * words are always seen by protocol drivers as right-justified, so the
+ * undefined (rx) or unused (tx) bits are always the most significant bits.
+ *
  * All SPI transfers start with the relevant chipselect active.  Normally
  * it stays selected until after the last transfer in a message.  Drivers
  * can affect the chipselect signal using cs_change:
@@ -462,6 +473,11 @@ static inline void spi_message_free(struct spi_message *m)
  * changes those settings, and must be called from a context that can sleep.
  * The changes take effect the next time the device is selected and data
  * is transferred to or from it.
+ *
+ * Note that this call wil fail if the protocol driver specifies an option
+ * that the underlying controller or its driver does not support.  For
+ * example, not all hardware supports wire transfers using nine bit words,
+ * LSB-first wire encoding, or active-high chipselects.
  */
 static inline int
 spi_setup(struct spi_device *spi)