linux-kernel - Re: [PATCH] virtio: Simplify DMA setting

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Message-ID: <42ba2840-bfa8-d530-4bcf-3eeee9403a31@redhat.com>
Date:   Mon, 10 Jan 2022 14:14:14 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>, mst@...hat.com
Cc:     virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] virtio: Simplify DMA setting


在 2022/1/8 下午3:08, Christophe JAILLET 写道:
> 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.


I'd expect to be more verbose here. E.g I see dma_supported() who has a 
brunch of checks need to be called if dma_mask is non-NULL.

Thanks


>
> Simplify code and remove some dead code accordingly.
>
>
> While at it, include directly <linux/dma-mapping.h> instead on relying on
> indirect inclusion.
>
> [1]: https://lkml.org/lkml/2021/6/7/398
>
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> ---
>   drivers/virtio/virtio_mmio.c           | 4 +---
>   drivers/virtio/virtio_pci_legacy_dev.c | 7 +++----
>   drivers/virtio/virtio_pci_modern_dev.c | 6 ++----
>   3 files changed, 6 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
> index 56128b9c46eb..aa1efa854de1 100644
> --- a/drivers/virtio/virtio_mmio.c
> +++ b/drivers/virtio/virtio_mmio.c
> @@ -617,9 +617,7 @@ static int virtio_mmio_probe(struct platform_device *pdev)
>   		rc = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64));
>   	}
>   	if (rc)
> -		rc = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32));
> -	if (rc)
> -		dev_warn(&pdev->dev, "Failed to enable 64-bit or 32-bit DMA.  Trying to continue, but this might not work.\n");
> +		dev_warn(&pdev->dev, "Failed to enable DMA.  Trying to continue, but this might not work.\n");
>   
>   	platform_set_drvdata(pdev, vm_dev);
>   
> diff --git a/drivers/virtio/virtio_pci_legacy_dev.c b/drivers/virtio/virtio_pci_legacy_dev.c
> index 677d1f68bc9b..52b1c4dd43fe 100644
> --- a/drivers/virtio/virtio_pci_legacy_dev.c
> +++ b/drivers/virtio/virtio_pci_legacy_dev.c
> @@ -2,6 +2,7 @@
>   
>   #include "linux/virtio_pci.h"
>   #include <linux/virtio_pci_legacy.h>
> +#include <linux/dma-mapping.h>
>   #include <linux/module.h>
>   #include <linux/pci.h>
>   
> @@ -26,9 +27,7 @@ int vp_legacy_probe(struct virtio_pci_legacy_device *ldev)
>   		return -ENODEV;
>   
>   	rc = dma_set_mask(&pci_dev->dev, DMA_BIT_MASK(64));
> -	if (rc) {
> -		rc = dma_set_mask_and_coherent(&pci_dev->dev, DMA_BIT_MASK(32));
> -	} else {
> +	if (!rc) {
>   		/*
>   		 * The virtio ring base address is expressed as a 32-bit PFN,
>   		 * with a page size of 1 << VIRTIO_PCI_QUEUE_ADDR_SHIFT.
> @@ -38,7 +37,7 @@ int vp_legacy_probe(struct virtio_pci_legacy_device *ldev)
>   	}
>   
>   	if (rc)
> -		dev_warn(&pci_dev->dev, "Failed to enable 64-bit or 32-bit DMA.  Trying to continue, but this might not work.\n");
> +		dev_warn(&pci_dev->dev, "Failed to enable DMA.  Trying to continue, but this might not work.\n");
>   
>   	rc = pci_request_region(pci_dev, 0, "virtio-pci-legacy");
>   	if (rc)
> diff --git a/drivers/virtio/virtio_pci_modern_dev.c b/drivers/virtio/virtio_pci_modern_dev.c
> index e8b3ff2b9fbc..830dc269d68f 100644
> --- a/drivers/virtio/virtio_pci_modern_dev.c
> +++ b/drivers/virtio/virtio_pci_modern_dev.c
> @@ -1,6 +1,7 @@
>   // SPDX-License-Identifier: GPL-2.0-or-later
>   
>   #include <linux/virtio_pci_modern.h>
> +#include <linux/dma-mapping.h>
>   #include <linux/module.h>
>   #include <linux/pci.h>
>   
> @@ -256,10 +257,7 @@ 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));
> -	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");
> +		dev_warn(&pci_dev->dev, "Failed to enable DMA.  Trying to continue, but this might not work.\n");
>   
>   	/* Device capability is only mandatory for devices that have
>   	 * device-specific configuration.