[PATCH v2 04/14] mtd: spinand: Fix odd byte addr and data phase in read and write reg op for Octal DTR mode

[Apurva Nandan <a-nandan@xxxxxx>]

In Octal DTR SPI mode, 2 bytes of data gets transmitted over one clock
cycle, and half-cycle instruction phases aren't supported yet. So,
every DTR spi_mem_op needs to have even nbytes in all phases for
non-erratic behaviour from the SPI controller.

The odd length cmd and dummy phases get handled by spimem_patch_op()
but the odd length address and data phases need to be handled according
to the use case. For example in Octal DTR mode, read register operation
has one byte long address and data phase. So it needs to extend it
by adding a suitable extra byte in addr and reading 2 bytes of data,
discarding the second byte.

Handle address and data phases for Octal DTR mode in read and write
register operations by adding a suitable extra byte in the address and
data phase.

Create spimem_patch_reg_op() helper function to ease setting up
read/write register operations in other functions, e.g. wait().

Signed-off-by: Apurva Nandan <a-nandan@xxxxxx>
---
 drivers/mtd/nand/spi/core.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/nand/spi/core.c b/drivers/mtd/nand/spi/core.c
index 11746d858f87..4da794ae728d 100644
--- a/drivers/mtd/nand/spi/core.c
+++ b/drivers/mtd/nand/spi/core.c
@@ -63,12 +63,29 @@ static void spinand_patch_op(const struct spinand_device *spinand,
 	}
 }
 
+static void spinand_patch_reg_op(const struct spinand_device *spinand,
+				 struct spi_mem_op *op)
+{
+	if (spinand->reg_proto == SPINAND_OCTAL_DTR) {
+		/*
+		 * Assigning same first and second byte will result in constant
+		 * bits on the SPI bus between positive and negative clock edges
+		 */
+		op->addr.val = (op->addr.val << 8) | op->addr.val;
+		op->addr.nbytes = 2;
+		op->data.nbytes = 2;
+	}
+
+	spinand_patch_op(spinand, op);
+}
+
 static int spinand_read_reg_op(struct spinand_device *spinand, u8 reg, u8 *val)
 {
 	struct spi_mem_op op = SPINAND_GET_FEATURE_OP(reg,
 						      spinand->scratchbuf);
 	int ret;
 
+	spinand_patch_reg_op(spinand, &op);
 	ret = spi_mem_exec_op(spinand->spimem, &op);
 	if (ret)
 		return ret;
@@ -82,7 +99,8 @@ static int spinand_write_reg_op(struct spinand_device *spinand, u8 reg, u8 val)
 	struct spi_mem_op op = SPINAND_SET_FEATURE_OP(reg,
 						      spinand->scratchbuf);
 
-	*spinand->scratchbuf = val;
+	spinand_patch_reg_op(spinand, &op);
+	memset(spinand->scratchbuf, val, op.data.nbytes);
 	return spi_mem_exec_op(spinand->spimem, &op);
 }
 
@@ -547,6 +565,7 @@ static int spinand_wait(struct spinand_device *spinand,
 	u8 status;
 	int ret;
 
+	spinand_patch_reg_op(spinand, &op);
 	ret = spi_mem_poll_status(spinand->spimem, &op, STATUS_BUSY, 0,
 				  initial_delay_us,
 				  poll_delay_us,
-- 
2.25.1