linux-kernel - [PATCH v7 12/20] mtd: spi-nor: core: do 2 byte reads for SR and FSR in DTR mode

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Date:   Fri, 22 May 2020 15:42:53 +0530
From:   Pratyush Yadav <p.yadav@...com>
To:     Tudor Ambarus <tudor.ambarus@...rochip.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Mark Brown <broonie@...nel.org>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Ludovic Desroches <ludovic.desroches@...rochip.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <linux-spi@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>
CC:     Pratyush Yadav <p.yadav@...com>, Sekhar Nori <nsekhar@...com>,
        Boris Brezillon <boris.brezillon@...labora.com>,
        Mason Yang <masonccyang@...c.com.tw>
Subject: [PATCH v7 12/20] mtd: spi-nor: core: do 2 byte reads for SR and FSR in DTR mode

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@...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 2ad248140b6c..5cb7e391cd29 100644
--- a/drivers/mtd/spi-nor/core.c
+++ b/drivers/mtd/spi-nor/core.c
@@ -350,7 +350,7 @@ 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.
  */
@@ -371,6 +371,11 @@ static int spi_nor_read_sr(struct spi_nor *nor, u8 *sr)
 			op.addr.nbytes = addr_bytes;
 			op.addr.val = 0;
 			op.dummy.nbytes = 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);
@@ -394,7 +399,8 @@ 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.
  */
@@ -415,6 +421,11 @@ static int spi_nor_read_fsr(struct spi_nor *nor, u8 *fsr)
 			op.addr.nbytes = addr_bytes;
 			op.addr.val = 0;
 			op.dummy.nbytes = 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);
-- 
2.26.2