[PATCH] mtd: rawnand: denali: fix a race condition when DMA is kicked

[PATCH] mtd: rawnand: denali: fix a race condition when DMA is kicked

[Masahiro Yamada]

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@pengutronix.de>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
---

 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);
-- 
2.7.4

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

[Miquel Raynal]

Hello,

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

> 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@pengutronix.de>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>


Thanks,
Miquèl

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

[Boris Brezillon]

On Thu, 13 Sep 2018 14:58:49 +0900
Masahiro Yamada <yamada.masahiro@socionext.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@pengutronix.de>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.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);