linux-kernel - Re: [PATCH 2/4 RESEND] dma-mapping: Add wrapper function to set dma

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Date:   Thu, 17 Mar 2022 17:19:36 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Michael Kelley <mikelley@...rosoft.com>, sthemmin@...rosoft.com,
        kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org,
        decui@...rosoft.com, rafael@...nel.org, lenb@...nel.org,
        lorenzo.pieralisi@....com, robh@...nel.org, kw@...ux.com,
        bhelgaas@...gle.com, hch@....de, m.szyprowski@...sung.com,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hyperv@...r.kernel.org, linux-pci@...r.kernel.org,
        iommu@...ts.linux-foundation.org
Subject: Re: [PATCH 2/4 RESEND] dma-mapping: Add wrapper function to set
 dma_coherent

On 2022-03-17 16:25, Michael Kelley via iommu wrote:
> Add a wrapper function to set dma_coherent, avoiding the need for
> complex #ifdef's when setting it in architecture independent code.

No. It might happen to work out on the architectures you're looking at, 
but if Hyper-V were ever to support, say, AArch32 VMs you might see the 
problem. arch_setup_dma_ops() is the tool for this job.

Robin.

> Signed-off-by: Michael Kelley <mikelley@...rosoft.com>
> ---
>   include/linux/dma-map-ops.h | 9 +++++++++
>   1 file changed, 9 insertions(+)
> 
> diff --git a/include/linux/dma-map-ops.h b/include/linux/dma-map-ops.h
> index 0d5b06b..3350e7a 100644
> --- a/include/linux/dma-map-ops.h
> +++ b/include/linux/dma-map-ops.h
> @@ -254,11 +254,20 @@ static inline bool dev_is_dma_coherent(struct device *dev)
>   {
>   	return dev->dma_coherent;
>   }
> +static inline void dev_set_dma_coherent(struct device *dev,
> +		bool coherent)
> +{
> +	dev->dma_coherent = coherent;
> +}
>   #else
>   static inline bool dev_is_dma_coherent(struct device *dev)
>   {
>   	return true;
>   }
> +static inline void dev_set_dma_coherent(struct device *dev,
> +		bool coherent)
> +{
> +}
>   #endif /* CONFIG_ARCH_HAS_DMA_COHERENCE_H */
>   
>   void *arch_dma_alloc(struct device *dev, size_t size, dma_addr_t *dma_handle,