[PATCH 03/10] spi: Add flag for no TX after a RX in the same Chip Select

[Lucas Tanure <tanureal@opensource.cirrus.com>]

Some controllers can't write to the bus after a read without
releasing the chip select, so add flag and a check in spi core

Signed-off-by: Lucas Tanure <tanureal@opensource.cirrus.com>
---
 drivers/spi/spi.c       | 11 +++++++++++
 include/linux/spi/spi.h |  1 +
 2 files changed, 12 insertions(+)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 65d14af9c015..1dbc8b6f1398 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -3724,6 +3724,17 @@ static int __spi_validate(struct spi_device *spi, struct spi_message *message)
 			return -EINVAL;
 	}
 
+	if (ctlr->flags & SPI_CONTROLLER_NO_TX_RX_CS) {
+		bool read = false;
+
+		list_for_each_entry(xfer, &message->transfers, transfer_list) {
+			if (read && xfer->tx_buf)
+				return -EINVAL;
+			if (xfer->rx_buf && !xfer->cs_change)
+				read = true;
+		}
+	}
+
 	message->status = -EINPROGRESS;
 
 	return 0;
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 8371bca13729..916b982dc2a1 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -514,6 +514,7 @@ struct spi_controller {
 #define SPI_CONTROLLER_MUST_TX		BIT(4)	/* requires tx */
 
 #define SPI_MASTER_GPIO_SS		BIT(5)	/* GPIO CS must select slave */
+#define SPI_CONTROLLER_NO_TX_RX_CS	BIT(6)	/* can't write after a read in the same CS */
 
 	/* flag indicating if the allocation of this struct is devres-managed */
 	bool			devm_allocated;
-- 
2.33.0