linux-kernel - Re: [PATCH v2 1/1] iommu/dma: Use DMA ops setter instead of direct assignment

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Message-ID: <58e77093-51e2-59a2-e413-164d83ecd9b8@arm.com>
Date:   Mon, 7 Feb 2022 15:55:32 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Joerg Roedel <jroedel@...e.de>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Cc:     Will Deacon <will@...nel.org>
Subject: Re: [PATCH v2 1/1] iommu/dma: Use DMA ops setter instead of direct
 assignment

On 2022-02-07 14:13, Andy Shevchenko wrote:
> Use DMA ops setter instead of direct assignment. Even we know that
> this module doesn't perform access to the dma_ops member of struct device,
> it's better to use setter to avoid potential problems in the future.

What potential problems are you imagining? This whole file is a DMA ops 
implementation, not driver code (and definitely not a module); if anyone 
removes the "select DMA_OPS" from CONFIG_IOMMU_DMA they deserve whatever 
breakage they get.

I concur that there's no major harm in using the helper here, but I also 
see no point in pretending that there's any value to abstracting the 
operation in this particular context.

Thanks,
Robin.

> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
> v2: rebased on top of the latest codebase
>   drivers/iommu/dma-iommu.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index d85d54f2b549..b585a3fdbc56 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -1482,7 +1482,7 @@ void iommu_setup_dma_ops(struct device *dev, u64 dma_base, u64 dma_limit)
>   	if (iommu_is_dma_domain(domain)) {
>   		if (iommu_dma_init_domain(domain, dma_base, dma_limit, dev))
>   			goto out_err;
> -		dev->dma_ops = &iommu_dma_ops;
> +		set_dma_ops(dev, &iommu_dma_ops);
>   	}
>   
>   	return;