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From:   Pratyush Yadav <p.yadav@ti.com>
To:     Tudor Ambarus <tudor.ambarus@microchip.com>,
        Miquel Raynal <miquel.raynal@bootlin.com>,
        Richard Weinberger <richard@nod.at>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        Mark Brown <broonie@kernel.org>,
        Nicolas Ferre <nicolas.ferre@microchip.com>,
        Alexandre Belloni <alexandre.belloni@bootlin.com>,
        Ludovic Desroches <ludovic.desroches@microchip.com>,
        <linux-mtd@lists.infradead.org>, <linux-kernel@vger.kernel.org>,
        <linux-spi@vger.kernel.org>, <linux-arm-kernel@lists.infradead.org>
CC:     Pratyush Yadav <p.yadav@ti.com>, Sekhar Nori <nsekhar@ti.com>
Subject: [PATCH v4 10/16] mtd: spi-nor: do 2 byte reads for SR and FSR in DTR mode
Date:   Sat, 25 Apr 2020 00:14:04 +0530
Message-ID: <20200424184410.8578-11-p.yadav@ti.com>
In-Reply-To: <20200424184410.8578-1-p.yadav@ti.com>
References: <20200424184410.8578-1-p.yadav@ti.com>
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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>
---
 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 3d181c7deda7..6eb2b1781972 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);
-- 
2.25.0