Re: [PATCH net-next 13/14] net: renesas: rswitch: Remove obsolete 32-bit DMA mask fallback

[Geert Uytterhoeven]

Hi Ruizhe,

Thanks for your patch!

On Thu, 3 Sept 2026 at 11:27, Ruizhe Zhou <zhouruizhe@xxxxxxxxxxx> wrote:
> The DMA API guarantees support for masks of 32 bits or wider and

Really?

> explicitly identifies retrying a 32-bit mask after a wider request as
> incorrect:
> https://docs.kernel.org/core-api/dma-api-howto.html#dma-addressing-capabilities

AFAIUI, that is only true iff the wider request is DMA_BIT_MASK(64).

> Remove the obsolete fallback while retaining the error check so that a
> genuine DMA setup failure still aborts initialization.

Have you tested this on actual hardware, with/without IOMMU support?

> Signed-off-by: Ruizhe Zhou <zhouruizhe@xxxxxxxxxxx>
> ---
>  drivers/net/ethernet/renesas/rswitch_main.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/net/ethernet/renesas/rswitch_main.c b/drivers/net/ethernet/renesas/rswitch_main.c
> index 755232994fcc..64b821ca02f8 100644
> --- a/drivers/net/ethernet/renesas/rswitch_main.c
> +++ b/drivers/net/ethernet/renesas/rswitch_main.c
> @@ -2162,11 +2162,8 @@ static int renesas_eth_sw_probe(struct platform_device *pdev)
>                 return -ENOMEM;
>
>         ret = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(40));
> -       if (ret < 0) {
> -               ret = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32));
> -               if (ret < 0)
> -                       return ret;
> -       }
> +       if (ret)
> +               return ret;
>
>         priv->gwca.index = AGENT_INDEX_GWCA;
>         priv->gwca.num_queues = min(RSWITCH_NUM_PORTS * NUM_QUEUES_PER_NDEV,

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds