spi: spidev: Enable control of inter-word delays

Commit b7bb367a added support for inserting delays in between
individual words within a single SPI transaction. This makes it
accessible from userspace.

WARNING: This delay is silently ignored unless the SPI controller
implements extra support for it. This is similar to how the in-kernel
users handle the other existing property, spi_transfer->word_delay.
Signed-off-by: Jan Kundrát <jan.kundrat@cesnet.cz>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spidev.c

@@ -276,17 +276,19 @@ static int spidev_message(struct spidev_data *spidev,
 		k_tmp->bits_per_word = u_tmp->bits_per_word;
 		k_tmp->delay_usecs = u_tmp->delay_usecs;
 		k_tmp->speed_hz = u_tmp->speed_hz;
+		k_tmp->word_delay_usecs = u_tmp->word_delay_usecs;
 		if (!k_tmp->speed_hz)
 			k_tmp->speed_hz = spidev->speed_hz;
 #ifdef VERBOSE
 		dev_dbg(&spidev->spi->dev,
-			"  xfer len %u %s%s%s%dbits %u usec %uHz\n",
+			"  xfer len %u %s%s%s%dbits %u usec %u usec %uHz\n",
 			u_tmp->len,
 			u_tmp->rx_buf ? "rx " : "",
 			u_tmp->tx_buf ? "tx " : "",
 			u_tmp->cs_change ? "cs " : "",
 			u_tmp->bits_per_word ? : spidev->spi->bits_per_word,
 			u_tmp->delay_usecs,
+			u_tmp->word_delay_usecs,
 			u_tmp->speed_hz ? : spidev->spi->max_speed_hz);
 #endif
 		spi_message_add_tail(k_tmp, &msg);

include/uapi/linux/spi/spidev.h

@@ -66,6 +66,9 @@
  * @delay_usecs: If nonzero, how long to delay after the last bit transfer
  *	before optionally deselecting the device before the next transfer.
  * @cs_change: True to deselect device before starting the next transfer.
+ * @word_delay_usecs: If nonzero, how long to wait between words within one
+ *	transfer. This property needs explicit support in the SPI controller,
+ *	otherwise it is silently ignored.
  *
  * This structure is mapped directly to the kernel spi_transfer structure;
  * the fields have the same meanings, except of course that the pointers
@@ -100,7 +103,8 @@ struct spi_ioc_transfer {
 	__u8		cs_change;
 	__u8		tx_nbits;
 	__u8		rx_nbits;
-	__u16		pad;
+	__u8		word_delay_usecs;
+	__u8		pad;
 
 	/* If the contents of 'struct spi_ioc_transfer' ever change
 	 * incompatibly, then the ioctl number (currently 0) must change;