Re: [RFC PATCH v7 2/5] iommu/dma: Add a new dma_map_ops of get_merge_boundary()

[Marek Szyprowski <m.szyprowski@samsung.com>]

Hi,

On 2019-06-20 10:50, Yoshihiro Shimoda wrote:
> This patch adds a new dma_map_ops of get_merge_boundary() to
> expose the DMA merge boundary if the domain type is IOMMU_DOMAIN_DMA.
>
> Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
> ---
>   drivers/iommu/dma-iommu.c | 11 +++++++++++
>   1 file changed, 11 insertions(+)
>
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index 205d694..9950cb5 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -1091,6 +1091,16 @@ static int iommu_dma_get_sgtable(struct device *dev, struct sg_table *sgt,
>   	return ret;
>   }
>   
> +static unsigned long iommu_dma_get_merge_boundary(struct device *dev)
> +{
> +	struct iommu_domain *domain = iommu_get_dma_domain(dev);
> +
> +	if (domain->type != IOMMU_DOMAIN_DMA)
> +		return 0;	/* can't merge */
> +
> +	return (1 << __ffs(domain->pgsize_bitmap)) - 1;
> +}

I really wonder if there is any IOMMU, which doesn't support 4KiB pages. 
Cannot you simply assume that the merge boundary is 4KiB and avoid 
adding this new API?

> +
>   static const struct dma_map_ops iommu_dma_ops = {
>   	.alloc			= iommu_dma_alloc,
>   	.free			= iommu_dma_free,
> @@ -1106,6 +1116,7 @@ static const struct dma_map_ops iommu_dma_ops = {
>   	.sync_sg_for_device	= iommu_dma_sync_sg_for_device,
>   	.map_resource		= iommu_dma_map_resource,
>   	.unmap_resource		= iommu_dma_unmap_resource,
> +	.get_merge_boundary	= iommu_dma_get_merge_boundary,
>   };
>   
>   /*

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland

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