linux-kernel - Re: [PATCH] dma-mapping: Stub out dma_{alloc,free,map}

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Message-ID: <7cf90a89-b381-48ae-98bc-1316022e03b6@linaro.org>
Date: Mon, 16 Jun 2025 12:21:11 +0100
From: James Clark <james.clark@...aro.org>
To: hch@....de
Cc: olteanv@...il.com, broonie@...nel.org, oe-kbuild-all@...ts.linux.dev,
 arnd@...db.de, larisa.grigore@....com, Frank.li@....com,
 linux-spi@...r.kernel.org, imx@...ts.linux.dev,
 linux-kernel@...r.kernel.org, kernel test robot <lkp@...el.com>,
 Marek Szyprowski <m.szyprowski@...sung.com>,
 Robin Murphy <robin.murphy@....com>, iommu@...ts.linux.dev
Subject: Re: [PATCH] dma-mapping: Stub out dma_{alloc,free,map}_pages() API



On 16/06/2025 12:17 pm, James Clark wrote:
> The implementations are in mapping.c which requires HAS_DMA so stub them
> out if not present. This is required for some drivers to pass randconfig
> builds.
> 

So the commit message makes it seem like this fixes an existing issue 
and it would need a fixes: tag. But I didn't add one because it seems 
like it would only hit new users like in the linked patchset. It might 
be better to add a tag but it was changed 5 years ago and nobody hit it 
until now so I'm not sure.

> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202506160036.t9VDxF6p-lkp@intel.com/
> Signed-off-by: James Clark <james.clark@...aro.org>
> ---
>   include/linux/dma-mapping.h | 28 +++++++++++++++++++++-------
>   1 file changed, 21 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index 55c03e5fe8cb..766f28a0e11f 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -161,6 +161,12 @@ void *dma_vmap_noncontiguous(struct device *dev, size_t size,
>   void dma_vunmap_noncontiguous(struct device *dev, void *vaddr);
>   int dma_mmap_noncontiguous(struct device *dev, struct vm_area_struct *vma,
>   		size_t size, struct sg_table *sgt);
> +struct page *dma_alloc_pages(struct device *dev, size_t size,
> +		dma_addr_t *dma_handle, enum dma_data_direction dir, gfp_t gfp);
> +void dma_free_pages(struct device *dev, size_t size, struct page *page,
> +		dma_addr_t dma_handle, enum dma_data_direction dir);
> +int dma_mmap_pages(struct device *dev, struct vm_area_struct *vma,
> +		size_t size, struct page *page);
>   #else /* CONFIG_HAS_DMA */
>   static inline dma_addr_t dma_map_page_attrs(struct device *dev,
>   		struct page *page, size_t offset, size_t size,
> @@ -291,6 +297,21 @@ static inline int dma_mmap_noncontiguous(struct device *dev,
>   {
>   	return -EINVAL;
>   }
> +static inline struct page *dma_alloc_pages(struct device *dev, size_t size,
> +		dma_addr_t *dma_handle, enum dma_data_direction dir, gfp_t gfp)
> +{
> +	return NULL;
> +}
> +static inline void dma_free_pages(struct device *dev, size_t size,
> +		struct page *page, dma_addr_t dma_handle,
> +		enum dma_data_direction dir)
> +{
> +}
> +static inline int dma_mmap_pages(struct device *dev, struct vm_area_struct *vma,
> +				 size_t size, struct page *page)
> +{
> +	return -EINVAL;
> +}
>   #endif /* CONFIG_HAS_DMA */
>   
>   #ifdef CONFIG_IOMMU_DMA
> @@ -438,13 +459,6 @@ static inline bool dma_need_unmap(struct device *dev)
>   }
>   #endif /* !CONFIG_HAS_DMA || !CONFIG_DMA_NEED_SYNC */
>   
> -struct page *dma_alloc_pages(struct device *dev, size_t size,
> -		dma_addr_t *dma_handle, enum dma_data_direction dir, gfp_t gfp);
> -void dma_free_pages(struct device *dev, size_t size, struct page *page,
> -		dma_addr_t dma_handle, enum dma_data_direction dir);
> -int dma_mmap_pages(struct device *dev, struct vm_area_struct *vma,
> -		size_t size, struct page *page);
> -
>   static inline void *dma_alloc_noncoherent(struct device *dev, size_t size,
>   		dma_addr_t *dma_handle, enum dma_data_direction dir, gfp_t gfp)
>   {