Re: [PATCH v1 1/2] iommu: export iommu_get_dma_domain()

[Robin Murphy <robin.murphy@arm.com>]

On 28/09/2026 6:38 am, Jianfeng Liu wrote:
> drm/msm needs to recover the physical address behind a DMA address of
> imported dma-bufs: with CONFIG_DMABUF_DEBUG=y the attachment sg_table
> it hands to importers carries no struct page, and msm has to translate
> sg_dma_address() back to a physical address through the attaching
> device's DMA-API domain to map such buffers into its own pagetables
> (see the follow-up drm/msm patch).
> 
> Export the helper so modularized drivers can use it.

NAK. Read the comment - this is an internal helper for iommu-dma 
(currently the only IOMMU_DOMAIN_DMA implementation) and is definitely 
not for random drivers to abuse. In fact it should really move to 
iommu-priv.h now that we have that.

If you want to do sketchy things with your device's DMA domain then use 
the public iommu_get_domain_for_dev() interface like everyone else.

Thanks,
Robin.

> 
> Cc: Joerg Roedel <joro@8bytes.org>
> Cc: Will Deacon <will@kernel.org>
> Cc: iommu@lists.linux.dev
> 
> Signed-off-by: Jianfeng Liu <liujianfeng1994@gmail.com>
> ---
> 
>   drivers/iommu/iommu.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index cd1bca7ede9af..330f9a79248bd 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -2327,6 +2327,7 @@ struct iommu_domain *iommu_get_dma_domain(struct device *dev)
>   {
>   	return dev->iommu_group->default_domain;
>   }
> +EXPORT_SYMBOL_GPL(iommu_get_dma_domain);
>   
>   static void *iommu_make_pasid_array_entry(struct iommu_domain *domain,
>   					  struct iommu_attach_handle *handle)