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    SubjectRe: [PATCH RFC] swiotlb: Remove SWIOTLB overflow buffer support
    On Fri, Jul 06, 2012 at 05:06:12PM -0600, Shuah Khan wrote:
    > Remove SWIOTLB overflow buffer support and return DMA_ERROR_CODE
    > (a value of zero) to make it consistent with iommu implementation
    > on Intel, AMD, and swiotlb-xen.

    While this is a good forward step and this needs to be done eventually,
    you should first send out patches for the drivers that don't check
    for the DMA_ERROR_CODE when doing mapping. In other words for the
    drivers that map but don't call dma_mapping_error to check.

    When that is fixed and *all the drivers that don't call dma_mapping_error
    are fixed, then this patch makes sense.

    So for right now, NACK.

    Also you missed CC-ing fujita.tomonori@lab.ntt.co.jp, so let me add
    that to this email.

    *: for those that it makes sense. I am not sure if folks are still using
    ancient drivers..

    >
    > Tested only on x86.
    >
    > Signed-off-by: Shuah Khan <shuah.khan@hp.com>
    > ---
    > lib/swiotlb.c | 44 ++++++++------------------------------------
    > 1 file changed, 8 insertions(+), 36 deletions(-)
    >
    > diff --git a/lib/swiotlb.c b/lib/swiotlb.c
    > index 45bc1f8..7f0a5d1 100644
    > --- a/lib/swiotlb.c
    > +++ b/lib/swiotlb.c
    > @@ -15,6 +15,7 @@
    > * 05/09/10 linville Add support for syncing ranges, support syncing for
    > * DMA_BIDIRECTIONAL mappings, miscellaneous cleanup.
    > * 08/12/11 beckyb Add highmem support
    > + * 06/12 shuahkhan Remove io tlb overflow support
    > */
    >
    > #include <linux/cache.h>
    > @@ -66,13 +67,6 @@ static char *io_tlb_start, *io_tlb_end;
    > static unsigned long io_tlb_nslabs;
    >
    > /*
    > - * When the IOMMU overflows we return a fallback buffer. This sets the size.
    > - */
    > -static unsigned long io_tlb_overflow = 32*1024;
    > -
    > -static void *io_tlb_overflow_buffer;
    > -
    > -/*
    > * This is a free list describing the number of free entries available from
    > * each index
    > */
    > @@ -108,7 +102,6 @@ setup_io_tlb_npages(char *str)
    > return 1;
    > }
    > __setup("swiotlb=", setup_io_tlb_npages);
    > -/* make io_tlb_overflow tunable too? */
    >
    > unsigned long swiotlb_nr_tbl(void)
    > {
    > @@ -156,12 +149,6 @@ void __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
    > io_tlb_index = 0;
    > io_tlb_orig_addr = alloc_bootmem_pages(PAGE_ALIGN(io_tlb_nslabs * sizeof(phys_addr_t)));
    >
    > - /*
    > - * Get the overflow emergency buffer
    > - */
    > - io_tlb_overflow_buffer = alloc_bootmem_low_pages(PAGE_ALIGN(io_tlb_overflow));
    > - if (!io_tlb_overflow_buffer)
    > - panic("Cannot allocate SWIOTLB overflow buffer!\n");
    > if (verbose)
    > swiotlb_print_info();
    > }
    > @@ -195,7 +182,8 @@ swiotlb_init_with_default_size(size_t default_size, int verbose)
    > void __init
    > swiotlb_init(int verbose)
    > {
    > - swiotlb_init_with_default_size(64 * (1<<20), verbose); /* default to 64MB */
    > + /* default to 64MB */
    > + swiotlb_init_with_default_size(64 * (1<<20), verbose);
    > }
    >
    > /*
    > @@ -264,24 +252,12 @@ swiotlb_late_init_with_default_size(size_t default_size)
    >
    > memset(io_tlb_orig_addr, 0, io_tlb_nslabs * sizeof(phys_addr_t));
    >
    > - /*
    > - * Get the overflow emergency buffer
    > - */
    > - io_tlb_overflow_buffer = (void *)__get_free_pages(GFP_DMA,
    > - get_order(io_tlb_overflow));
    > - if (!io_tlb_overflow_buffer)
    > - goto cleanup4;
    > -
    > swiotlb_print_info();
    >
    > late_alloc = 1;
    >
    > return 0;
    >
    > -cleanup4:
    > - free_pages((unsigned long)io_tlb_orig_addr,
    > - get_order(io_tlb_nslabs * sizeof(phys_addr_t)));
    > - io_tlb_orig_addr = NULL;
    > cleanup3:
    > free_pages((unsigned long)io_tlb_list, get_order(io_tlb_nslabs *
    > sizeof(int)));
    > @@ -297,12 +273,10 @@ cleanup1:
    >
    > void __init swiotlb_free(void)
    > {
    > - if (!io_tlb_overflow_buffer)
    > + if (!io_tlb_orig_addr)
    > return;
    >
    > if (late_alloc) {
    > - free_pages((unsigned long)io_tlb_overflow_buffer,
    > - get_order(io_tlb_overflow));
    > free_pages((unsigned long)io_tlb_orig_addr,
    > get_order(io_tlb_nslabs * sizeof(phys_addr_t)));
    > free_pages((unsigned long)io_tlb_list, get_order(io_tlb_nslabs *
    > @@ -310,8 +284,6 @@ void __init swiotlb_free(void)
    > free_pages((unsigned long)io_tlb_start,
    > get_order(io_tlb_nslabs << IO_TLB_SHIFT));
    > } else {
    > - free_bootmem_late(__pa(io_tlb_overflow_buffer),
    > - PAGE_ALIGN(io_tlb_overflow));
    > free_bootmem_late(__pa(io_tlb_orig_addr),
    > PAGE_ALIGN(io_tlb_nslabs * sizeof(phys_addr_t)));
    > free_bootmem_late(__pa(io_tlb_list),
    > @@ -639,7 +611,7 @@ swiotlb_full(struct device *dev, size_t size, enum dma_data_direction dir,
    > printk(KERN_ERR "DMA: Out of SW-IOMMU space for %zu bytes at "
    > "device %s\n", size, dev ? dev_name(dev) : "?");
    >
    > - if (size <= io_tlb_overflow || !do_panic)
    > + if (!do_panic)
    > return;
    >
    > if (dir == DMA_BIDIRECTIONAL)
    > @@ -681,7 +653,7 @@ dma_addr_t swiotlb_map_page(struct device *dev, struct page *page,
    > map = map_single(dev, phys, size, dir);
    > if (!map) {
    > swiotlb_full(dev, size, dir, 1);
    > - map = io_tlb_overflow_buffer;
    > + return DMA_ERROR_CODE;
    > }
    >
    > dev_addr = swiotlb_virt_to_bus(dev, map);
    > @@ -691,7 +663,7 @@ dma_addr_t swiotlb_map_page(struct device *dev, struct page *page,
    > */
    > if (!dma_capable(dev, dev_addr, size)) {
    > swiotlb_tbl_unmap_single(dev, map, size, dir);
    > - dev_addr = swiotlb_virt_to_bus(dev, io_tlb_overflow_buffer);
    > + dev_addr = 0;
    > }
    >
    > return dev_addr;
    > @@ -910,7 +882,7 @@ EXPORT_SYMBOL(swiotlb_sync_sg_for_device);
    > int
    > swiotlb_dma_mapping_error(struct device *hwdev, dma_addr_t dma_addr)
    > {
    > - return (dma_addr == swiotlb_virt_to_bus(hwdev, io_tlb_overflow_buffer));
    > + return !dma_addr;
    > }
    > EXPORT_SYMBOL(swiotlb_dma_mapping_error);
    >
    > --
    > 1.7.9.5
    >
    >


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