linux-kernel - Re: [PATCH] virito-pci-modern: Remove useless DMA-32 fallback configuration

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Message-ID: <CACGkMEvFK9O1qzKAeihF-3EGDC=iOmszKUA8QoMnCv5ovrg8yw@mail.gmail.com>
Date:   Fri, 18 Mar 2022 10:21:47 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     cgel.zte@...il.com
Cc:     mst <mst@...hat.com>,
        virtualization <virtualization@...ts.linux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Minghao Chi <chi.minghao@....com.cn>,
        Zeal Robot <zealci@....com.cn>
Subject: Re: [PATCH] virito-pci-modern: Remove useless DMA-32 fallback configuration

On Fri, Mar 18, 2022 at 8:59 AM <cgel.zte@...il.com> wrote:
>
> From: Minghao Chi <chi.minghao@....com.cn>
>
> As stated in [1], dma_set_mask() with a 64-bit mask will never fail if
> dev->dma_mask is non-NULL.
> So, if it fails, the 32 bits case will also fail for the same reason.
>
> Simplify code and remove some dead code accordingly.
>
> [1]: https://lkml.org/lkml/2021/6/7/398
>
> Reported-by: Zeal Robot <zealci@....com.cn>
> Signed-off-by: Minghao Chi <chi.minghao@....com.cn>
> ---
>  drivers/virtio/virtio_pci_modern_dev.c | 3 ---
>  1 file changed, 3 deletions(-)
>
> diff --git a/drivers/virtio/virtio_pci_modern_dev.c b/drivers/virtio/virtio_pci_modern_dev.c
> index e8b3ff2b9fbc..dff0b15a239d 100644
> --- a/drivers/virtio/virtio_pci_modern_dev.c
> +++ b/drivers/virtio/virtio_pci_modern_dev.c
> @@ -255,9 +255,6 @@ int vp_modern_probe(struct virtio_pci_modern_device *mdev)
>         }
>
>         err = dma_set_mask_and_coherent(&pci_dev->dev, DMA_BIT_MASK(64));
> -       if (err)
> -               err = dma_set_mask_and_coherent(&pci_dev->dev,
> -                                               DMA_BIT_MASK(32));

So we had:

        if (!dev->dma_mask || !dma_supported(dev, mask))
                return -EIO;

in dma_set_mask(), any reason dma_supported() can't be false here?

Thanks

>         if (err)
>                 dev_warn(&pci_dev->dev, "Failed to enable 64-bit or 32-bit DMA.  Trying to continue, but this might not work.\n");
>
> --
> 2.25.1
>