Re: [PATCH 3/5] dma: Introduce dma_max_mapping_size()

["Lendacky, Thomas" <Thomas.Lendacky@amd.com>]

On 1/29/19 2:43 AM, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@suse.de>
> 
> The function returns the maximum size that can be mapped
> using DMA-API functions. The patch also adds the
> implementation for direct DMA and a new dma_map_ops pointer
> so that other implementations can expose their limit.
> 
> Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> Signed-off-by: Joerg Roedel <jroedel@suse.de>
> ---
>  Documentation/DMA-API.txt   |  8 ++++++++
>  include/linux/dma-mapping.h | 16 ++++++++++++++++
>  kernel/dma/direct.c         | 11 +++++++++++
>  3 files changed, 35 insertions(+)
> 
> diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt
> index e133ccd60228..acfe3d0f78d1 100644
> --- a/Documentation/DMA-API.txt
> +++ b/Documentation/DMA-API.txt
> @@ -195,6 +195,14 @@ Requesting the required mask does not alter the current mask.  If you
>  wish to take advantage of it, you should issue a dma_set_mask()
>  call to set the mask to the value returned.
>  
> +::
> +
> +	size_t
> +	dma_direct_max_mapping_size(struct device *dev);
> +
> +Returns the maximum size of a mapping for the device. The size parameter
> +of the mapping functions like dma_map_single(), dma_map_page() and
> +others should not be larger than the returned value.
>  
>  Part Id - Streaming DMA mappings
>  --------------------------------
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index f6ded992c183..a3ca8a71a704 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -130,6 +130,7 @@ struct dma_map_ops {
>  			enum dma_data_direction direction);
>  	int (*dma_supported)(struct device *dev, u64 mask);
>  	u64 (*get_required_mask)(struct device *dev);
> +	size_t (*max_mapping_size)(struct device *dev);
>  };
>  
>  #define DMA_MAPPING_ERROR		(~(dma_addr_t)0)
> @@ -257,6 +258,8 @@ static inline void dma_direct_sync_sg_for_cpu(struct device *dev,
>  }
>  #endif
>  
> +size_t dma_direct_max_mapping_size(struct device *dev);
> +
>  #ifdef CONFIG_HAS_DMA
>  #include <asm/dma-mapping.h>
>  
> @@ -440,6 +443,19 @@ static inline int dma_mapping_error(struct device *dev, dma_addr_t dma_addr)
>  	return 0;
>  }
>  
> +static inline size_t dma_max_mapping_size(struct device *dev)
> +{
> +	const struct dma_map_ops *ops = get_dma_ops(dev);
> +	size_t size = SIZE_MAX;
> +
> +	if (dma_is_direct(ops))
> +		size = dma_direct_max_mapping_size(dev);
> +	else if (ops && ops->max_mapping_size)
> +		size = ops->max_mapping_size(dev);
> +
> +	return size;
> +}
> +
>  void *dma_alloc_attrs(struct device *dev, size_t size, dma_addr_t *dma_handle,
>  		gfp_t flag, unsigned long attrs);
>  void dma_free_attrs(struct device *dev, size_t size, void *cpu_addr,
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index 355d16acee6d..6310ad01f915 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -380,3 +380,14 @@ int dma_direct_supported(struct device *dev, u64 mask)
>  	 */
>  	return mask >= __phys_to_dma(dev, min_mask);
>  }
> +
> +size_t dma_direct_max_mapping_size(struct device *dev)
> +{
> +	size_t size = SIZE_MAX;
> +
> +	/* If SWIOTLB is active, use its maximum mapping size */
> +	if (is_swiotlb_active())
> +		size = swiotlb_max_mapping_size(dev);
> +
> +	return size;
> +}

When I build with these patches and with the virtio devices as modules I
get a build failure. Looks like this needs an EXPORT_SYMBOL() (I'm
assuming EXPORT_SYMBOL for DMA functions and not EXPORT_SYMBOL_GPL?).

Thanks,
Tom

>