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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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