Re: [PATCH v9 2/5] iommu/dma: Add a new dma_map_ops of get_merge_boundary()

[Robin Murphy <robin.murphy@arm.com>]

On 26/07/2019 09:31, 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>
> Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
> ---
>   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 a7f9c3e..2992ce4 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -1085,6 +1085,16 @@ 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)

Did you actually need this check? In principle, if the default domain is 
not of type IOMMU_DOMAIN_DMA then the device should be assigned 
dma_direct_ops rather than iommu_dma_ops, thus it shouldn't be possible 
to get here. If you did manage to hit a case where the domain type 
didn't match the ops it would be interesting to figure out how.

Robin.

> +		return 0;	/* can't merge */
> +
> +	return (1UL << __ffs(domain->pgsize_bitmap)) - 1;
> +}
> +
>   static const struct dma_map_ops iommu_dma_ops = {
>   	.alloc			= iommu_dma_alloc,
>   	.free			= iommu_dma_free,
> @@ -1100,6 +1110,7 @@ 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,
>   };
>   
>   /*
> 
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