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    SubjectRe: [PATCH v3 2/4] dma-iommu: Add iommu_dma_opt_mapping_size()
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    On 06/06/2022 10:30, John Garry wrote:
    > Add the IOMMU callback for DMA mapping API dma_opt_mapping_size(), which
    > allows the drivers to know the optimal mapping limit and thus limit the
    > requested IOVA lengths.
    >
    > This value is based on the IOVA rcache range limit, as IOVAs allocated
    > above this limit must always be newly allocated, which may be quite slow.
    >

    Can I please get some sort of ack from the IOMMU people on this one?

    Thanks,
    John

    EOM

    > Signed-off-by: John Garry <john.garry@huawei.com>
    > Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
    > ---
    > drivers/iommu/dma-iommu.c | 6 ++++++
    > drivers/iommu/iova.c | 5 +++++
    > include/linux/iova.h | 2 ++
    > 3 files changed, 13 insertions(+)
    >
    > diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
    > index f90251572a5d..9e1586447ee8 100644
    > --- a/drivers/iommu/dma-iommu.c
    > +++ b/drivers/iommu/dma-iommu.c
    > @@ -1459,6 +1459,11 @@ static unsigned long iommu_dma_get_merge_boundary(struct device *dev)
    > return (1UL << __ffs(domain->pgsize_bitmap)) - 1;
    > }
    >
    > +static size_t iommu_dma_opt_mapping_size(void)
    > +{
    > + return iova_rcache_range();
    > +}
    > +
    > static const struct dma_map_ops iommu_dma_ops = {
    > .alloc = iommu_dma_alloc,
    > .free = iommu_dma_free,
    > @@ -1479,6 +1484,7 @@ static const struct dma_map_ops iommu_dma_ops = {
    > .map_resource = iommu_dma_map_resource,
    > .unmap_resource = iommu_dma_unmap_resource,
    > .get_merge_boundary = iommu_dma_get_merge_boundary,
    > + .opt_mapping_size = iommu_dma_opt_mapping_size,
    > };
    >
    > /*
    > diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
    > index db77aa675145..9f00b58d546e 100644
    > --- a/drivers/iommu/iova.c
    > +++ b/drivers/iommu/iova.c
    > @@ -26,6 +26,11 @@ static unsigned long iova_rcache_get(struct iova_domain *iovad,
    > static void free_cpu_cached_iovas(unsigned int cpu, struct iova_domain *iovad);
    > static void free_iova_rcaches(struct iova_domain *iovad);
    >
    > +unsigned long iova_rcache_range(void)
    > +{
    > + return PAGE_SIZE << (IOVA_RANGE_CACHE_MAX_SIZE - 1);
    > +}
    > +
    > static int iova_cpuhp_dead(unsigned int cpu, struct hlist_node *node)
    > {
    > struct iova_domain *iovad;
    > diff --git a/include/linux/iova.h b/include/linux/iova.h
    > index 320a70e40233..c6ba6d95d79c 100644
    > --- a/include/linux/iova.h
    > +++ b/include/linux/iova.h
    > @@ -79,6 +79,8 @@ static inline unsigned long iova_pfn(struct iova_domain *iovad, dma_addr_t iova)
    > int iova_cache_get(void);
    > void iova_cache_put(void);
    >
    > +unsigned long iova_rcache_range(void);
    > +
    > void free_iova(struct iova_domain *iovad, unsigned long pfn);
    > void __free_iova(struct iova_domain *iovad, struct iova *iova);
    > struct iova *alloc_iova(struct iova_domain *iovad, unsigned long size,

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