spi: introduce `delay` field for `spi_transfer` + spi_transfer_delay_exec()

The change introduces the `delay` field to the `spi_transfer` struct as an
`struct spi_delay` type.
This intends to eventually replace `delay_usecs`.

But, since there are many users of `delay_usecs`, this needs some
intermediate work.
A helper called `spi_transfer_delay_exec()` is also added, which maintains
backwards compatibility with `delay_usecs`, by assigning the value to
`delay` if non-zero.
This should maintain backwards compatibility with current users of
`udelay_usecs`.
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Link: https://lore.kernel.org/r/20190926105147.7839-9-alexandru.ardelean@analog.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi.c

@@ -1248,8 +1248,7 @@ static int spi_transfer_one_message(struct spi_controller *ctlr,
 		if (msg->status != -EINPROGRESS)
 			goto out;
 
-		if (xfer->delay_usecs)
-			_spi_transfer_delay_ns(xfer->delay_usecs * 1000);
+		spi_transfer_delay_exec(xfer);
 
 		if (xfer->cs_change) {
 			if (list_is_last(&xfer->transfer_list,
@@ -3026,10 +3025,11 @@ struct spi_replaced_transfers *spi_replace_transfers(
 		/* add to list */
 		list_add(&xfer->transfer_list, rxfer->replaced_after);
 
-		/* clear cs_change and delay_usecs for all but the last */
+		/* clear cs_change and delay for all but the last */
 		if (i) {
 			xfer->cs_change = false;
 			xfer->delay_usecs = 0;
+			xfer->delay.value = 0;
 		}
 	}
 

include/linux/spi/spi.h

@@ -778,6 +778,9 @@ extern void spi_res_release(struct spi_controller *ctlr,
  * @cs_change: affects chipselect after this transfer completes
  * @cs_change_delay: delay between cs deassert and assert when
  *      @cs_change is set and @spi_transfer is not the last in @spi_message
+ * @delay: delay to be introduced after this transfer before
+ *	(optionally) changing the chipselect status, then starting
+ *	the next transfer or completing this @spi_message.
  * @delay_usecs: microseconds to delay after this transfer before
  *	(optionally) changing the chipselect status, then starting
  *	the next transfer or completing this @spi_message.
@@ -896,6 +899,7 @@ struct spi_transfer {
 #define	SPI_NBITS_QUAD		0x04 /* 4bits transfer */
 	u8		bits_per_word;
 	u16		delay_usecs;
+	struct spi_delay	delay;
 	struct spi_delay	cs_change_delay;
 	struct spi_delay	word_delay;
 	u32		speed_hz;
@@ -1003,6 +1007,20 @@ spi_transfer_del(struct spi_transfer *t)
 	list_del(&t->transfer_list);
 }
 
+static inline int
+spi_transfer_delay_exec(struct spi_transfer *t)
+{
+	struct spi_delay d;
+
+	if (t->delay_usecs) {
+		d.value = t->delay_usecs;
+		d.unit = SPI_DELAY_UNIT_USECS;
+		return spi_delay_exec(&d, NULL);
+	}
+
+	return spi_delay_exec(&t->delay, t);
+}
+
 /**
  * spi_message_init_with_transfers - Initialize spi_message and append transfers
  * @m: spi_message to be initialized