Re: [PATCH v2] ata: sata_rcar: Fix DMA boundary mask

[Ulf Hansson]

On Tue, 11 Aug 2020 at 10:17, Geert Uytterhoeven
<geert+renesas@xxxxxxxxx> wrote:
>
> Before commit 9495b7e92f716ab2 ("driver core: platform: Initialize
> dma_parms for platform devices"), the R-Car SATA device didn't have DMA
> parameters.  Hence the DMA boundary mask supplied by its driver was
> silently ignored, as __scsi_init_queue() doesn't check the return value
> of dma_set_seg_boundary(), and the default value of 0xffffffff was used.
>
> Now the device has gained DMA parameters, the driver-supplied value is
> used, and the following warning is printed on Salvator-XS:
>
>     DMA-API: sata_rcar ee300000.sata: mapping sg segment across boundary [start=0x00000000ffffe000] [end=0x00000000ffffefff] [boundary=0x000000001ffffffe]
>     WARNING: CPU: 5 PID: 38 at kernel/dma/debug.c:1233 debug_dma_map_sg+0x298/0x300
>
> (the range of start/end values depend on whether IOMMU support is
>  enabled or not)
>
> The issue here is that SATA_RCAR_DMA_BOUNDARY doesn't have bit 0 set, so
> any typical end value, which is odd, will trigger the check.
>
> Fix this by increasing the DMA boundary value by 1.
>
> Fixes: 8bfbeed58665dbbf ("sata_rcar: correct 'sata_rcar_sht'")
> Fixes: 9495b7e92f716ab2 ("driver core: platform: Initialize dma_parms for platform devices")
> Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Reviewed-by: Sergei Shtylyov <sergei.shtylyov@xxxxxxxxxxxxxxxxxx>
> Tested-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx>
> Cc: stable <stable@xxxxxxxxxxxxxxx>

Reviewed-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx>

Kind regards
Uffe

> ---
> v2:
>   - Add Reviewed-by, Tested-by, Cc.
>
> This is a fix for a regression in v5.7-rc5 that fell through the cracks.
> https://lore.kernel.org/linux-ide/20200513110426.22472-1-geert+renesas@xxxxxxxxx/
>
> As by default the DMA debug code prints the first error only, this issue
> may be hidden on plain v5.7-rc5, where the FCP driver triggers a similar
> warning.  Merging commit dd844fb8e50b12e6 ("media: platform: fcp: Set
> appropriate DMA parameters", in v5.8-rc1) from the media tree fixes the
> FCP issue, and exposes the SATA issue.
>
> I added the second fixes tag because that commit is already being
> backported to stable kernels, and this patch thus needs backporting,
> too.
> ---
>  drivers/ata/sata_rcar.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/ata/sata_rcar.c b/drivers/ata/sata_rcar.c
> index 141ac600b64c87ef..44b0ed8f6bb8a120 100644
> --- a/drivers/ata/sata_rcar.c
> +++ b/drivers/ata/sata_rcar.c
> @@ -120,7 +120,7 @@
>  /* Descriptor table word 0 bit (when DTA32M = 1) */
>  #define SATA_RCAR_DTEND                        BIT(0)
>
> -#define SATA_RCAR_DMA_BOUNDARY         0x1FFFFFFEUL
> +#define SATA_RCAR_DMA_BOUNDARY         0x1FFFFFFFUL
>
>  /* Gen2 Physical Layer Control Registers */
>  #define RCAR_GEN2_PHY_CTL1_REG         0x1704
> --
> 2.17.1
>