linux-kernel - Re: [PATCH 21/26] iommu/dma: Refactor iommu_dma_get

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Date:   Mon, 29 Apr 2019 15:08:58 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Christoph Hellwig <hch@....de>
Cc:     Joerg Roedel <joro@...tes.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 21/26] iommu/dma: Refactor iommu_dma_get_sgtable

On 22/04/2019 18:59, Christoph Hellwig wrote:
> Inline __iommu_dma_get_sgtable_page into the main function, and use the
> fact that __iommu_dma_get_pages return NULL for remapped contigous
> allocations to simplify the code flow a bit.

Yeah, even I was a bit dubious about the readability of "if (page)... 
else if (pages)..." that my attempt ended up with, so I don't really 
have anything to complain about here.

Reviewed-by: Robin Murphy <robin.murphy@....com>

> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>   drivers/iommu/dma-iommu.c | 45 +++++++++++++++------------------------
>   1 file changed, 17 insertions(+), 28 deletions(-)
> 
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index acdfe866cb29..138b85e675c8 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -1070,42 +1070,31 @@ static int iommu_dma_mmap(struct device *dev, struct vm_area_struct *vma,
>   	return __iommu_dma_mmap(pages, size, vma);
>   }
>   
> -static int __iommu_dma_get_sgtable_page(struct sg_table *sgt, struct page *page,
> -		size_t size)
> -{
> -	int ret = sg_alloc_table(sgt, 1, GFP_KERNEL);
> -
> -	if (!ret)
> -		sg_set_page(sgt->sgl, page, PAGE_ALIGN(size), 0);
> -	return ret;
> -}
> -
>   static int iommu_dma_get_sgtable(struct device *dev, struct sg_table *sgt,
>   		void *cpu_addr, dma_addr_t dma_addr, size_t size,
>   		unsigned long attrs)
>   {
> -	unsigned int count = PAGE_ALIGN(size) >> PAGE_SHIFT;
> -	struct page **pages;
> +	struct page *page;
> +	int ret;
>   
> -	if (!is_vmalloc_addr(cpu_addr)) {
> -		struct page *page = virt_to_page(cpu_addr);
> -		return __iommu_dma_get_sgtable_page(sgt, page, size);
> -	}
> +	if (is_vmalloc_addr(cpu_addr)) {
> +		struct page **pages = __iommu_dma_get_pages(cpu_addr);
>   
> -	if (attrs & DMA_ATTR_FORCE_CONTIGUOUS) {
> -		/*
> -		 * DMA_ATTR_FORCE_CONTIGUOUS allocations are always remapped,
> -		 * hence in the vmalloc space.
> -		 */
> -		struct page *page = vmalloc_to_page(cpu_addr);
> -		return __iommu_dma_get_sgtable_page(sgt, page, size);
> +		if (pages) {
> +			return sg_alloc_table_from_pages(sgt, pages,
> +					PAGE_ALIGN(size) >> PAGE_SHIFT,
> +					0, size, GFP_KERNEL);
> +		}
> +
> +		page = vmalloc_to_page(cpu_addr);
> +	} else {
> +		page = virt_to_page(cpu_addr);
>   	}
>   
> -	pages = __iommu_dma_get_pages(cpu_addr);
> -	if (WARN_ON_ONCE(!pages))
> -		return -ENXIO;
> -	return sg_alloc_table_from_pages(sgt, pages, count, 0, size,
> -					 GFP_KERNEL);
> +	ret = sg_alloc_table(sgt, 1, GFP_KERNEL);
> +	if (!ret)
> +		sg_set_page(sgt->sgl, page, PAGE_ALIGN(size), 0);
> +	return ret;
>   }
>   
>   static const struct dma_map_ops iommu_dma_ops = {
>