linux-kernel - Re: [PATCH] mtd: rawnand: denali: fix a race condition when DMA is kicked

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Message-ID: <20180917143244.2e55fbac@bbrezillon>
Date:   Mon, 17 Sep 2018 14:32:44 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     linux-mtd@...ts.infradead.org,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Steffen Trumtrar <s.trumtrar@...gutronix.de>,
        Marek Vasut <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        linux-kernel@...r.kernel.org,
        Brian Norris <computersforpeace@...il.com>,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH] mtd: rawnand: denali: fix a race condition when DMA is
 kicked

On Thu, 13 Sep 2018 14:58:49 +0900
Masahiro Yamada <yamada.masahiro@...ionext.com> wrote:

> 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")
> Reported-by: Steffen Trumtrar <s.trumtrar@...gutronix.de>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>

Queued to master.

Thanks,

Boris

> ---
> 
>  drivers/mtd/nand/raw/denali.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/mtd/nand/raw/denali.c b/drivers/mtd/nand/raw/denali.c
> index 67b2065..b864b93 100644
> --- a/drivers/mtd/nand/raw/denali.c
> +++ b/drivers/mtd/nand/raw/denali.c
> @@ -596,6 +596,12 @@ static int denali_dma_xfer(struct denali_nand_info *denali, void *buf,
>  	}
>  
>  	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);