linux-kernel - Re: [PATCH] mtd: rawnand: atmel: Unmap streaming DMA mappings

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Date:   Fri, 29 Jul 2022 12:59:55 +0200
From:   Alexander Dahl <ada@...rsis.com>
To:     linux-mtd@...ts.infradead.org
Cc:     Tudor Ambarus <tudor.ambarus@...rochip.com>,
        miquel.raynal@...tlin.com, richard@....at, vigneshr@...com,
        peda@...ntia.se, nicolas.ferre@...rochip.com,
        alexandre.belloni@...tlin.com, claudiu.beznea@...rochip.com,
        bbrezillon@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] mtd: rawnand: atmel: Unmap streaming DMA mappings

Hello Tudor,

Am Donnerstag, 28. Juli 2022, 09:40:14 CEST schrieb Tudor Ambarus:
> Every dma_map_single() call should have its dma_unmap_single() counterpart,
> because the DMA address space is a shared resource and one could render the
> machine unusable by consuming all DMA addresses.
> 
> Cc: stable@...r.kernel.org
> Fixes: f88fc122cc34 ("mtd: nand: Cleanup/rework the atmel_nand driver")
> Signed-off-by: Tudor Ambarus <tudor.ambarus@...rochip.com>
> ---
>  drivers/mtd/nand/raw/atmel/nand-controller.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/mtd/nand/raw/atmel/nand-controller.c
> b/drivers/mtd/nand/raw/atmel/nand-controller.c index
> 6ef14442c71a..330d2dafdd2d 100644
> --- a/drivers/mtd/nand/raw/atmel/nand-controller.c
> +++ b/drivers/mtd/nand/raw/atmel/nand-controller.c
> @@ -405,6 +405,7 @@ static int atmel_nand_dma_transfer(struct
> atmel_nand_controller *nc,
> 
>  	dma_async_issue_pending(nc->dmac);
>  	wait_for_completion(&finished);
> +	dma_unmap_single(nc->dev, buf_dma, len, dir);
> 
>  	return 0;

Acked-by: Alexander Dahl <ada@...rsis.com>

After studying 
https://www.kernel.org/doc/html/latest/core-api/dma-api-howto.html
this seems like the correct thing to do to me.

I was made aware of this patch in IRC, after discussing a strange lzo 
decompression and/or page reading error with Richard after upgrading from 
kernel v5.2.21-rt13 to v5.15.49-rt47.

Now testing this on top of 5.15.49-rt47 on two boards, both with Microchip 
sama5d27c 128MiB SiP and Spansion S34ML02G1 raw nand flash. Will report later.

Thanks and greets
Alex