linux-kernel - [PATCH] mtd: nand: wait for tWHR after NAND_CMD_STATUS / NAND_CMD

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Date:   Tue, 26 Sep 2017 12:39:24 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     linux-mtd@...ts.infradead.org
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        linux-kernel@...r.kernel.org,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Brian Norris <computersforpeace@...il.com>,
        Richard Weinberger <richard@....at>,
        David Woodhouse <dwmw2@...radead.org>
Subject: [PATCH] mtd: nand: wait for tWHR after NAND_CMD_STATUS / NAND_CMD_READID

Read Status and Read ID require tWHR before reading the first data.
Insert a very short wait to make sure to meet the spec.

I have not seen any problem report for now, but nand_command() and
nand_command_lP() are generic hooks, so it makes sense to implement
fail-safe code here.

Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
---

 drivers/mtd/nand/nand_base.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index b1cf32c..55c0ba5 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -742,9 +742,12 @@ static void nand_command(struct mtd_info *mtd, unsigned int command,
 	case NAND_CMD_ERASE1:
 	case NAND_CMD_ERASE2:
 	case NAND_CMD_SEQIN:
+	case NAND_CMD_SET_FEATURES:
+		return;
+
 	case NAND_CMD_STATUS:
 	case NAND_CMD_READID:
-	case NAND_CMD_SET_FEATURES:
+		ndelay(200);	/* tWHR */
 		return;
 
 	case NAND_CMD_RESET:
@@ -871,9 +874,12 @@ static void nand_command_lp(struct mtd_info *mtd, unsigned int command,
 	case NAND_CMD_ERASE1:
 	case NAND_CMD_ERASE2:
 	case NAND_CMD_SEQIN:
+	case NAND_CMD_SET_FEATURES:
+		return;
+
 	case NAND_CMD_STATUS:
 	case NAND_CMD_READID:
-	case NAND_CMD_SET_FEATURES:
+		ndelay(200);	/* tWHR */
 		return;
 
 	case NAND_CMD_RNDIN:
-- 
2.7.4