linux-kernel - [PATCH v2 2/6] mtd: spi-nor: spansion: write 2 bytes when disabling Octal DTR mode

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Date:   Mon, 31 May 2021 23:47:53 +0530
From:   Pratyush Yadav <p.yadav@...com>
To:     Tudor Ambarus <tudor.ambarus@...rochip.com>,
        Michael Walle <michael@...le.cc>,
        Pratyush Yadav <p.yadav@...com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Mark Brown <broonie@...nel.org>,
        <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <linux-spi@...r.kernel.org>
Subject: [PATCH v2 2/6] mtd: spi-nor: spansion: write 2 bytes when disabling Octal DTR mode

The Octal DTR configuration is stored in the CFR5V register. This
register is 1 byte wide. But 1 byte long transactions are not allowed in
8D-8D-8D mode. Since the next byte address does not contain any
register, it is safe to write any value to it. Write a 0 to it.

Signed-off-by: Pratyush Yadav <p.yadav@...com>
---

(no changes since v1)

 drivers/mtd/spi-nor/spansion.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/drivers/mtd/spi-nor/spansion.c b/drivers/mtd/spi-nor/spansion.c
index ee82dcd75310..e6bf5c9eee6a 100644
--- a/drivers/mtd/spi-nor/spansion.c
+++ b/drivers/mtd/spi-nor/spansion.c
@@ -65,10 +65,18 @@ static int spi_nor_cypress_octal_dtr_enable(struct spi_nor *nor, bool enable)
 	if (ret)
 		return ret;
 
-	if (enable)
-		*buf = SPINOR_REG_CYPRESS_CFR5V_OCT_DTR_EN;
-	else
-		*buf = SPINOR_REG_CYPRESS_CFR5V_OCT_DTR_DS;
+	if (enable) {
+		buf[0] = SPINOR_REG_CYPRESS_CFR5V_OCT_DTR_EN;
+	} else {
+		/*
+		 * The register is 1-byte wide, but 1-byte transactions are not
+		 * allowed in 8D-8D-8D mode. Since there is no register at the
+		 * next location, just initialize the value to 0 and let the
+		 * transaction go on.
+		 */
+		buf[0] = SPINOR_REG_CYPRESS_CFR5V_OCT_DTR_DS;
+		buf[1] = 0;
+	}
 
 	op = (struct spi_mem_op)
 		SPI_MEM_OP(SPI_MEM_OP_CMD(SPINOR_OP_WR_ANY_REG, 1),
@@ -76,7 +84,7 @@ static int spi_nor_cypress_octal_dtr_enable(struct spi_nor *nor, bool enable)
 					   SPINOR_REG_CYPRESS_CFR5V,
 					   1),
 			   SPI_MEM_OP_NO_DUMMY,
-			   SPI_MEM_OP_DATA_OUT(1, buf, 1));
+			   SPI_MEM_OP_DATA_OUT(enable ? 1 : 2, buf, 1));
 
 	if (!enable)
 		spi_nor_spimem_setup_op(nor, &op, SNOR_PROTO_8_8_8_DTR);
-- 
2.30.0