On Thu, Mar 03, 2016 at 02:54:26AM +0800, Yong Wu wrote: > Sometimes it is not worth for the iommu allocating big chunks. > Here we enable DMA_ATTR_ALLOC_SINGLE_PAGES which could help avoid to > allocate big chunks while iommu allocating buffer. > > More information about this attribute, please check Doug's commit[1]. > > [1]: https://lkml.org/lkml/2016/1/11/720 > > Cc: Robin Murphy <[email protected]> > Suggested-by: Douglas Anderson <[email protected]> > Signed-off-by: Yong Wu <[email protected]> > --- > > Our video drivers may soon use this. > > arch/arm64/mm/dma-mapping.c | 4 ++-- > drivers/iommu/dma-iommu.c | 14 ++++++++++---- > include/linux/dma-iommu.h | 4 ++-- > 3 files changed, 14 insertions(+), 8 deletions(-) > > diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c > index 331c4ca..3225e3ca 100644 > --- a/arch/arm64/mm/dma-mapping.c > +++ b/arch/arm64/mm/dma-mapping.c > @@ -562,8 +562,8 @@ static void *__iommu_alloc_attrs(struct device *dev, > size_t size, > struct page **pages; > pgprot_t prot = __get_dma_pgprot(attrs, PAGE_KERNEL, coherent); > > - pages = iommu_dma_alloc(dev, iosize, gfp, ioprot, handle, > - flush_page); > + pages = iommu_dma_alloc(dev, iosize, gfp, ioprot, attrs, > + handle, flush_page); > if (!pages) > return NULL; > > diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c > index 72d6182..3569cb6 100644 > --- a/drivers/iommu/dma-iommu.c > +++ b/drivers/iommu/dma-iommu.c > @@ -190,7 +190,8 @@ static void __iommu_dma_free_pages(struct page **pages, > int count) > kvfree(pages); > } > > -static struct page **__iommu_dma_alloc_pages(unsigned int count, gfp_t gfp) > +static struct page **__iommu_dma_alloc_pages(unsigned int count, gfp_t gfp, > + struct dma_attrs *attrs) > { > struct page **pages; > unsigned int i = 0, array_size = count * sizeof(*pages); > @@ -203,6 +204,10 @@ static struct page **__iommu_dma_alloc_pages(unsigned > int count, gfp_t gfp) > if (!pages) > return NULL; > > + /* Go straight to 4K chunks if caller says it's OK. */ > + if (dma_get_attr(DMA_ATTR_ALLOC_SINGLE_PAGES, attrs)) > + order = 0;
I have a slight snag with this, in that you don't consult the IOMMU pgsize_bitmap at any point, and assume that it can map pages at the same granularity as the CPU. The documentation for DMA_ATTR_ALLOC_SINGLE_PAGES seems to be weaker than that. Will
