[RFC PATCH 05/15] spi: sprd: convert transfer word delay to spi_delay struct

[Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx>]

The Spreadtrum SPI driver is the only user of the `word_delay` field in
the `spi_transfer` struct.

This change converts the field to use the `spi_delay` struct. This also
enforces the users to specify the delay unit to be `SPI_DELAY_UNIT_SCK`.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx>
---
 drivers/spi/spi-sprd.c  | 11 +++++++++--
 include/linux/spi/spi.h |  4 ++--
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/drivers/spi/spi-sprd.c b/drivers/spi/spi-sprd.c
index 1b7eebb72c07..5634cd3e4a8d 100644
--- a/drivers/spi/spi-sprd.c
+++ b/drivers/spi/spi-sprd.c
@@ -671,9 +671,13 @@ static void sprd_spi_set_speed(struct sprd_spi *ss, u32 speed_hz)
 
 static void sprd_spi_init_hw(struct sprd_spi *ss, struct spi_transfer *t)
 {
+	struct spi_delay *d = &t->word_delay;
 	u16 word_delay, interval;
 	u32 val;
 
+	if (t->unit != SPI_DELAY_UNIT_SCK)
+		return -EINVAL;
+
 	val = readl_relaxed(ss->base + SPRD_SPI_CTL7);
 	val &= ~(SPRD_SPI_SCK_REV | SPRD_SPI_NG_TX | SPRD_SPI_NG_RX);
 	/* Set default chip selection, clock phase and clock polarity */
@@ -686,7 +690,7 @@ static void sprd_spi_init_hw(struct sprd_spi *ss, struct spi_transfer *t)
 	 * formula as below per datasheet:
 	 * interval time (source clock cycles) = interval * 4 + 10.
 	 */
-	word_delay = clamp_t(u16, t->word_delay, SPRD_SPI_MIN_DELAY_CYCLE,
+	word_delay = clamp_t(u16, d->value, SPRD_SPI_MIN_DELAY_CYCLE,
 			     SPRD_SPI_MAX_DELAY_CYCLE);
 	interval = DIV_ROUND_UP(word_delay - 10, 4);
 	ss->word_delay = interval * 4 + 10;
@@ -719,13 +723,16 @@ static int sprd_spi_setup_transfer(struct spi_device *sdev,
 	struct sprd_spi *ss = spi_controller_get_devdata(sdev->controller);
 	u8 bits_per_word = t->bits_per_word;
 	u32 val, mode = 0;
+	int ret;
 
 	ss->len = t->len;
 	ss->tx_buf = t->tx_buf;
 	ss->rx_buf = t->rx_buf;
 
 	ss->hw_mode = sdev->mode;
-	sprd_spi_init_hw(ss, t);
+	ret = sprd_spi_init_hw(ss, t);
+	if (ret)
+		return ret;
 
 	/* Set tansfer speed and valid bits */
 	sprd_spi_set_speed(ss, t->speed_hz);
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 9ded3f44d58e..16397b210e0c 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -759,7 +759,7 @@ extern void spi_res_release(struct spi_controller *ctlr,
  *	the next transfer or completing this @spi_message.
  * @word_delay_usecs: microseconds to inter word delay after each word size
  *	(set by bits_per_word) transmission.
- * @word_delay: clock cycles to inter word delay after each word size
+ * @word_delay: inter word delay to be introduced after each word size
  *	(set by bits_per_word) transmission.
  * @effective_speed_hz: the effective SCK-speed that was used to
  *      transfer this transfer. Set to 0 if the spi bus driver does
@@ -847,8 +847,8 @@ struct spi_transfer {
 	u8		word_delay_usecs;
 	u16		delay_usecs;
 	struct spi_delay	cs_change_delay;
+	struct spi_delay	word_delay;
 	u32		speed_hz;
-	u16		word_delay;
 
 	u32		effective_speed_hz;
 
-- 
2.20.1