[PATCH v16 07/15] mtd: spi-nor: core: do 2 byte reads for SR and FSR in DTR mode

[Pratyush Yadav <p.yadav@ti.com>]

Some controllers, like the cadence qspi controller, have trouble reading
only 1 byte in DTR mode. So, do 2 byte reads for SR and FSR commands in
DTR mode, and then discard the second byte.

Signed-off-by: Pratyush Yadav <p.yadav@ti.com>
Reviewed-by: Tudor Ambarus <tudor.ambarus@microchip.com>
---
 drivers/mtd/spi-nor/core.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
index b5bb4d6cffc1..b83bf5ed2b2d 100644
--- a/drivers/mtd/spi-nor/core.c
+++ b/drivers/mtd/spi-nor/core.c
@@ -370,7 +370,7 @@ int spi_nor_write_disable(struct spi_nor *nor)
  * spi_nor_read_sr() - Read the Status Register.
  * @nor:	pointer to 'struct spi_nor'.
  * @sr:		pointer to a DMA-able buffer where the value of the
- *              Status Register will be written.
+ *              Status Register will be written. Should be at least 2 bytes.
  *
  * Return: 0 on success, -errno otherwise.
  */
@@ -388,6 +388,11 @@ static int spi_nor_read_sr(struct spi_nor *nor, u8 *sr)
 		if (nor->reg_proto == SNOR_PROTO_8_8_8_DTR) {
 			op.addr.nbytes = nor->params->rdsr_addr_nbytes;
 			op.dummy.nbytes = nor->params->rdsr_dummy;
+			/*
+			 * We don't want to read only one byte in DTR mode. So,
+			 * read 2 and then discard the second byte.
+			 */
+			op.data.nbytes = 2;
 		}
 
 		spi_nor_spimem_setup_op(nor, &op, nor->reg_proto);
@@ -408,7 +413,8 @@ static int spi_nor_read_sr(struct spi_nor *nor, u8 *sr)
  * spi_nor_read_fsr() - Read the Flag Status Register.
  * @nor:	pointer to 'struct spi_nor'
  * @fsr:	pointer to a DMA-able buffer where the value of the
- *              Flag Status Register will be written.
+ *              Flag Status Register will be written. Should be at least 2
+ *              bytes.
  *
  * Return: 0 on success, -errno otherwise.
  */
@@ -426,6 +432,11 @@ static int spi_nor_read_fsr(struct spi_nor *nor, u8 *fsr)
 		if (nor->reg_proto == SNOR_PROTO_8_8_8_DTR) {
 			op.addr.nbytes = nor->params->rdsr_addr_nbytes;
 			op.dummy.nbytes = nor->params->rdsr_dummy;
+			/*
+			 * We don't want to read only one byte in DTR mode. So,
+			 * read 2 and then discard the second byte.
+			 */
+			op.data.nbytes = 2;
 		}
 
 		spi_nor_spimem_setup_op(nor, &op, nor->reg_proto);
-- 
2.28.0