[PATCH] dma-direct: enable mmap for !CONFIG_MMU

[PATCH] dma-direct: enable mmap for !CONFIG_MMU

[Christoph Hellwig]

nommu configfs can trivially map the coherent allocations to user space,
as no actual page table setup is required and the kernel and the user
space programs share the same address space.

Fixes: 62fcee9a3bd7 ("dma-mapping: remove CONFIG_ARCH_NO_COHERENT_DMA_MMAP")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reported-by: dillon min <dillon.minfei@gmail.com>
Reviewed-by: Vladimir Murzin <vladimir.murzin@arm.com>
Tested-by: dillon min <dillon.minfei@gmail.com>
---
 kernel/dma/Kconfig  |  1 +
 kernel/dma/direct.c | 14 --------------
 2 files changed, 1 insertion(+), 14 deletions(-)

diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig
index d006668c0027d2..e0dae570a51530 100644
--- a/kernel/dma/Kconfig
+++ b/kernel/dma/Kconfig
@@ -71,6 +71,7 @@ config SWIOTLB
 # in the pagetables
 #
 config DMA_NONCOHERENT_MMAP
+	default y if !MMU
 	bool
 
 config DMA_REMAP
diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 0a4881e59aa7d6..9ec6a5c3fc578c 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -459,7 +459,6 @@ int dma_direct_get_sgtable(struct device *dev, struct sg_table *sgt,
 	return ret;
 }
 
-#ifdef CONFIG_MMU
 bool dma_direct_can_mmap(struct device *dev)
 {
 	return dev_is_dma_coherent(dev) ||
@@ -485,19 +484,6 @@ int dma_direct_mmap(struct device *dev, struct vm_area_struct *vma,
 	return remap_pfn_range(vma, vma->vm_start, pfn + vma->vm_pgoff,
 			user_count << PAGE_SHIFT, vma->vm_page_prot);
 }
-#else /* CONFIG_MMU */
-bool dma_direct_can_mmap(struct device *dev)
-{
-	return false;
-}
-
-int dma_direct_mmap(struct device *dev, struct vm_area_struct *vma,
-		void *cpu_addr, dma_addr_t dma_addr, size_t size,
-		unsigned long attrs)
-{
-	return -ENXIO;
-}
-#endif /* CONFIG_MMU */
 
 int dma_direct_supported(struct device *dev, u64 mask)
 {
-- 
2.26.2


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Re: [PATCH] dma-direct: enable mmap for !CONFIG_MMU

[Vladimir Murzin]

On 6/15/20 8:05 AM, Christoph Hellwig wrote:
> nommu configfs can trivially map the coherent allocations to user space,
> as no actual page table setup is required and the kernel and the user
> space programs share the same address space.
> 
> Fixes: 62fcee9a3bd7 ("dma-mapping: remove CONFIG_ARCH_NO_COHERENT_DMA_MMAP")
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Reported-by: dillon min <dillon.minfei@gmail.com>
> Reviewed-by: Vladimir Murzin <vladimir.murzin@arm.com>
> Tested-by: dillon min <dillon.minfei@gmail.com>
> ---
>  kernel/dma/Kconfig  |  1 +
>  kernel/dma/direct.c | 14 --------------
>  2 files changed, 1 insertion(+), 14 deletions(-)
> 
> diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig
> index d006668c0027d2..e0dae570a51530 100644
> --- a/kernel/dma/Kconfig
> +++ b/kernel/dma/Kconfig
> @@ -71,6 +71,7 @@ config SWIOTLB
>  # in the pagetables
>  #
>  config DMA_NONCOHERENT_MMAP
> +	default y if !MMU
>  	bool
>  
>  config DMA_REMAP
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index 0a4881e59aa7d6..9ec6a5c3fc578c 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -459,7 +459,6 @@ int dma_direct_get_sgtable(struct device *dev, struct sg_table *sgt,
>  	return ret;
>  }
>  
> -#ifdef CONFIG_MMU
>  bool dma_direct_can_mmap(struct device *dev)
>  {
>  	return dev_is_dma_coherent(dev) ||
> @@ -485,19 +484,6 @@ int dma_direct_mmap(struct device *dev, struct vm_area_struct *vma,
>  	return remap_pfn_range(vma, vma->vm_start, pfn + vma->vm_pgoff,
>  			user_count << PAGE_SHIFT, vma->vm_page_prot);
>  }
> -#else /* CONFIG_MMU */
> -bool dma_direct_can_mmap(struct device *dev)
> -{
> -	return false;
> -}
> -
> -int dma_direct_mmap(struct device *dev, struct vm_area_struct *vma,
> -		void *cpu_addr, dma_addr_t dma_addr, size_t size,
> -		unsigned long attrs)
> -{
> -	return -ENXIO;
> -}
> -#endif /* CONFIG_MMU */
>  
>  int dma_direct_supported(struct device *dev, u64 mask)
>  {
> 

LGTM. Should it go stable as well?

Cheers
Vladimir

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Re: [PATCH] dma-direct: enable mmap for !CONFIG_MMU

[Christoph Hellwig]

On Tue, Jun 16, 2020 at 01:02:11PM +0100, Vladimir Murzin wrote:
> LGTM. Should it go stable as well?

I think it will be picked up automatically eventually due to the Fixes
tag.

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