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powerpc/kernel/iommu: Align size for IOMMU_PAGE_SIZE() to save TCEs
Currently both iommu_alloc_coherent() and iommu_free_coherent() align the desired allocation size to PAGE_SIZE, and gets system pages and IOMMU mappings (TCEs) for that value. When IOMMU_PAGE_SIZE < PAGE_SIZE, this behavior may cause unnecessary TCEs to be created for mapping the whole system page. Example: - PAGE_SIZE = 64k, IOMMU_PAGE_SIZE() = 4k - iommu_alloc_coherent() is called for 128 bytes - 1 system page (64k) is allocated - 16 IOMMU pages (16 x 4k) are allocated (16 TCEs used) It would be enough to use a single TCE for this, so 15 TCEs are wasted in the process. Update iommu_*_coherent() to make sure the size alignment happens only for IOMMU_PAGE_SIZE() before calling iommu_alloc() and iommu_free(). Also, on iommu_range_alloc(), replace ALIGN(n, 1 << tbl->it_page_shift) with IOMMU_PAGE_ALIGN(n, tbl), which is easier to read and does the same. Signed-off-by: Leonardo Bras <leobras.c@gmail.com> Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20210318174414.684630-1-leobras.c@gmail.com
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parent
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commit
3c0468d445
1 changed files with 6 additions and 5 deletions
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@ -889,6 +889,7 @@ void *iommu_alloc_coherent(struct device *dev, struct iommu_table *tbl,
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unsigned int order;
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unsigned int nio_pages, io_order;
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struct page *page;
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size_t size_io = size;
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size = PAGE_ALIGN(size);
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order = get_order(size);
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@ -915,8 +916,9 @@ void *iommu_alloc_coherent(struct device *dev, struct iommu_table *tbl,
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memset(ret, 0, size);
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/* Set up tces to cover the allocated range */
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nio_pages = size >> tbl->it_page_shift;
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io_order = get_iommu_order(size, tbl);
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size_io = IOMMU_PAGE_ALIGN(size_io, tbl);
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nio_pages = size_io >> tbl->it_page_shift;
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io_order = get_iommu_order(size_io, tbl);
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mapping = iommu_alloc(dev, tbl, ret, nio_pages, DMA_BIDIRECTIONAL,
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mask >> tbl->it_page_shift, io_order, 0);
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if (mapping == DMA_MAPPING_ERROR) {
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@ -931,10 +933,9 @@ void iommu_free_coherent(struct iommu_table *tbl, size_t size,
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void *vaddr, dma_addr_t dma_handle)
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{
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if (tbl) {
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unsigned int nio_pages;
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size_t size_io = IOMMU_PAGE_ALIGN(size, tbl);
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unsigned int nio_pages = size_io >> tbl->it_page_shift;
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size = PAGE_ALIGN(size);
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nio_pages = size >> tbl->it_page_shift;
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iommu_free(tbl, dma_handle, nio_pages);
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size = PAGE_ALIGN(size);
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free_pages((unsigned long)vaddr, get_order(size));
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