[PATCH 1/2] Add support for 32 bit DMA for 32 bit machines

[Matthew Wilcox]

On Thu, Feb 28, 2013 at 07:49:13PM +0000, Chayan Biswas wrote:
> We set the DMA mask to 32 bit if the system is a 32 bit system. We also
> try to set to 32 bit DMA if setting the 64 bit DMA fails, and clean up
> if both fails.

What problem are you solving here?  If the system is 32-bit, setting the
DMA mask to 64-bit should be harmless.  The DMA mask tells the system
what the device is capable of -- this doesn't change if the system
happens to be 32-bit.

> Signed-off-by: Chayan Biswas <Chayan.Biswas at sandisk.com>
> ---
>  drivers/block/nvme.c |   19 +++++++++++++++++--
>  1 files changed, 17 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/block/nvme.c b/drivers/block/nvme.c
> index 993c014..4b706b5 100644
> --- a/drivers/block/nvme.c
> +++ b/drivers/block/nvme.c
> @@ -42,6 +42,7 @@
> 
>  #include <asm-generic/io-64-nonatomic-lo-hi.h>
> 
> +#define IS_DMA64               (sizeof(dma_addr_t) == 8)
>  #define NVME_Q_DEPTH 1024
>  #define SQ_SIZE(depth)         (depth * sizeof(struct nvme_command))
>  #define CQ_SIZE(depth)         (depth * sizeof(struct nvme_completion))
> @@ -1662,8 +1663,21 @@ static int __devinit nvme_probe(struct pci_dev *pdev,
>         INIT_LIST_HEAD(&dev->namespaces);
>         dev->pci_dev = pdev;
>         pci_set_drvdata(pdev, dev);
> -       dma_set_mask(&pdev->dev, DMA_BIT_MASK(64));
> -       dma_set_coherent_mask(&pdev->dev, DMA_BIT_MASK(64));
> +       if (IS_DMA64) {
> +               if (dma_set_mask(&pdev->dev, DMA_BIT_MASK(64)) != 0) {
> +                       if (dma_set_mask(&pdev->dev, DMA_BIT_MASK(32)) != 0)
> +                               goto fail_set_dma_mask;
> +
> +                       dma_set_coherent_mask(&pdev->dev, DMA_BIT_MASK(32));
> +               } else {
> +                       dma_set_coherent_mask(&pdev->dev, DMA_BIT_MASK(64));
> +               }
> +       } else {
> +               if (dma_set_mask(&pdev->dev, DMA_BIT_MASK(32)) != 0)
> +                       goto fail_set_dma_mask;
> +
> +               dma_set_coherent_mask(&pdev->dev, DMA_BIT_MASK(32));
> +       }
>         result = nvme_set_instance(dev);
>         if (result)
>                 goto disable;
> @@ -1705,6 +1719,7 @@ static int __devinit nvme_probe(struct pci_dev *pdev,
>         iounmap(dev->bar);
>   disable_msix:
>         pci_disable_msix(pdev);
> + fail_set_dma_mask:
>         nvme_release_instance(dev);
>         nvme_release_prp_pools(dev);
>   disable:
> --
> 1.7.1
> 
> 
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