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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        Steffen Trumtrar <s.trumtrar@pengutronix.de>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Miquel Raynal <miquel.raynal@bootlin.com>,
        Boris Brezillon <boris.brezillon@bootlin.com>
Subject: [PATCH 4.18 41/88] mtd: rawnand: denali: fix a race condition when DMA is kicked
Date:   Thu, 27 Sep 2018 11:03:22 +0200
Message-Id: <20180927090305.746943986@linuxfoundation.org>
In-Reply-To: <20180927090300.631426620@linuxfoundation.org>
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4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Masahiro Yamada <yamada.masahiro@socionext.com>

commit cf51e4b9c34407bf0c3d9b582b7837e047e1df47 upstream.

I thought the read-back of the DMA_ENABLE register was unnecessary
(at least it is working on my boards), then deleted it in commit
586a2c52909d ("mtd: nand: denali: squash denali_enable_dma() helper
into caller").  Sorry, I was wrong - it caused a timing issue on
Cyclone5 SoCFPGAs.

Revive the register read-back, commenting why this is necessary.

Fixes: 586a2c52909d ("mtd: nand: denali: squash denali_enable_dma() helper into caller")
Cc: <stable@vger.kernel.org>
Reported-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/mtd/nand/raw/denali.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/drivers/mtd/nand/raw/denali.c
+++ b/drivers/mtd/nand/raw/denali.c
@@ -604,6 +604,12 @@ static int denali_dma_xfer(struct denali
 	}
 
 	iowrite32(DMA_ENABLE__FLAG, denali->reg + DMA_ENABLE);
+	/*
+	 * The ->setup_dma() hook kicks DMA by using the data/command
+	 * interface, which belongs to a different AXI port from the
+	 * register interface.  Read back the register to avoid a race.
+	 */
+	ioread32(denali->reg + DMA_ENABLE);
 
 	denali_reset_irq(denali);
 	denali->setup_dma(denali, dma_addr, page, write);