[RFC,v7,2/5] iommu/dma: Add a new dma_map_ops of get_merge_boundary()
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Message ID 1561020610-953-3-git-send-email-yoshihiro.shimoda.uh@renesas.com
State New
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Series
  • treewide: improve R-Car SDHI performance
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Commit Message

Yoshihiro Shimoda June 20, 2019, 8:50 a.m. UTC
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(+)

Comments

Marek Szyprowski June 21, 2019, 7:59 a.m. UTC | #1
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
Christoph Hellwig June 24, 2019, 6:21 a.m. UTC | #2
On Fri, Jun 21, 2019 at 09:59:21AM +0200, Marek Szyprowski wrote:
> 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?

No idea if we have one, but I would not be surprised if one shows
up on a system only built to run with 64k pages for example.

Either way the abstraction seems light and self-explanatory, so I see
now reason not to have it even if we assume it would always return
4k, especially as we'd also still need a flag at the dma_map_ops level
to indicate if segement merging is supported at all.

Patch
diff mbox series

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;
+}
+
 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,
 };
 
 /*