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

diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
index 560be51..24208cd 100644 (file)
--- a/arch/powerpc/kernel/iommu.c
+++ b/arch/powerpc/kernel/iommu.c
@@ -889,6 +889,7 @@ void *iommu_alloc_coherent(struct device *dev, struct iommu_table *tbl,
        unsigned int order;
        unsigned int nio_pages, io_order;
        struct page *page;
+       size_t size_io = size;
 
        size = PAGE_ALIGN(size);
        order = get_order(size);
@@ -915,8 +916,9 @@ void *iommu_alloc_coherent(struct device *dev, struct iommu_table *tbl,
        memset(ret, 0, size);
 
        /* Set up tces to cover the allocated range */
-       nio_pages = size >> tbl->it_page_shift;
-       io_order = get_iommu_order(size, tbl);
+       size_io = IOMMU_PAGE_ALIGN(size_io, tbl);
+       nio_pages = size_io >> tbl->it_page_shift;
+       io_order = get_iommu_order(size_io, tbl);
        mapping = iommu_alloc(dev, tbl, ret, nio_pages, DMA_BIDIRECTIONAL,
                              mask >> tbl->it_page_shift, io_order, 0);
        if (mapping == DMA_MAPPING_ERROR) {
@@ -931,10 +933,9 @@ void iommu_free_coherent(struct iommu_table *tbl, size_t size,
                         void *vaddr, dma_addr_t dma_handle)
 {
        if (tbl) {
-               unsigned int nio_pages;
+               size_t size_io = IOMMU_PAGE_ALIGN(size, tbl);
+               unsigned int nio_pages = size_io >> tbl->it_page_shift;
 
-               size = PAGE_ALIGN(size);
-               nio_pages = size >> tbl->it_page_shift;
                iommu_free(tbl, dma_handle, nio_pages);
                size = PAGE_ALIGN(size);
                free_pages((unsigned long)vaddr, get_order(size));