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    SubjectRe: [RFC PATCH 1/7] swiotlb: Instead of tracking the end of the swiotlb region just calculate it
    On Wed, Oct 03, 2012 at 05:38:47PM -0700, Alexander Duyck wrote:
    > In the case of swiotlb we already have the start of the region and the number
    > of slabs that give us the region size. Instead of having to call
    > virt_to_phys on two pointers we can just take advantage of the fact that the
    > region is linear and just compute the end based on the start plus the size.

    Why not take advantage of 'the fact that the region is linear' and just
    pre-compute the end in swiotlb_init_with_tbl?

    That way the logic in is_swiotlb_buffer is even simpler?

    >
    > Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
    > ---
    >
    > lib/swiotlb.c | 25 ++++++++++++-------------
    > 1 files changed, 12 insertions(+), 13 deletions(-)
    >
    > diff --git a/lib/swiotlb.c b/lib/swiotlb.c
    > index f114bf6..5cc4d4e 100644
    > --- a/lib/swiotlb.c
    > +++ b/lib/swiotlb.c
    > @@ -57,11 +57,11 @@ int swiotlb_force;
    > * swiotlb_tbl_sync_single_*, to see if the memory was in fact allocated by this
    > * API.
    > */
    > -static char *io_tlb_start, *io_tlb_end;
    > +static char *io_tlb_start;
    >
    > /*
    > - * The number of IO TLB blocks (in groups of 64) between io_tlb_start and
    > - * io_tlb_end. This is command line adjustable via setup_io_tlb_npages.
    > + * The number of IO TLB blocks (in groups of 64).
    > + * This is command line adjustable via setup_io_tlb_npages.
    > */
    > static unsigned long io_tlb_nslabs;
    >
    > @@ -128,11 +128,11 @@ void swiotlb_print_info(void)
    > phys_addr_t pstart, pend;
    >
    > pstart = virt_to_phys(io_tlb_start);
    > - pend = virt_to_phys(io_tlb_end);
    > + pend = pstart + bytes;
    >
    > printk(KERN_INFO "software IO TLB [mem %#010llx-%#010llx] (%luMB) mapped at [%p-%p]\n",
    > (unsigned long long)pstart, (unsigned long long)pend - 1,
    > - bytes >> 20, io_tlb_start, io_tlb_end - 1);
    > + bytes >> 20, io_tlb_start, io_tlb_start + bytes - 1);
    > }
    >
    > void __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
    > @@ -143,12 +143,10 @@ void __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
    >
    > io_tlb_nslabs = nslabs;
    > io_tlb_start = tlb;
    > - io_tlb_end = io_tlb_start + bytes;
    >
    > /*
    > * Allocate and initialize the free list array. This array is used
    > * to find contiguous free memory regions of size up to IO_TLB_SEGSIZE
    > - * between io_tlb_start and io_tlb_end.
    > */
    > io_tlb_list = alloc_bootmem_pages(PAGE_ALIGN(io_tlb_nslabs * sizeof(int)));
    > for (i = 0; i < io_tlb_nslabs; i++)
    > @@ -254,14 +252,12 @@ swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs)
    >
    > io_tlb_nslabs = nslabs;
    > io_tlb_start = tlb;
    > - io_tlb_end = io_tlb_start + bytes;
    >
    > memset(io_tlb_start, 0, bytes);
    >
    > /*
    > * Allocate and initialize the free list array. This array is used
    > * to find contiguous free memory regions of size up to IO_TLB_SEGSIZE
    > - * between io_tlb_start and io_tlb_end.
    > */
    > io_tlb_list = (unsigned int *)__get_free_pages(GFP_KERNEL,
    > get_order(io_tlb_nslabs * sizeof(int)));
    > @@ -304,7 +300,6 @@ cleanup3:
    > sizeof(int)));
    > io_tlb_list = NULL;
    > cleanup2:
    > - io_tlb_end = NULL;
    > io_tlb_start = NULL;
    > io_tlb_nslabs = 0;
    > return -ENOMEM;
    > @@ -339,8 +334,10 @@ void __init swiotlb_free(void)
    >
    > static int is_swiotlb_buffer(phys_addr_t paddr)
    > {
    > - return paddr >= virt_to_phys(io_tlb_start) &&
    > - paddr < virt_to_phys(io_tlb_end);
    > + phys_addr_t swiotlb_start = virt_to_phys(io_tlb_start);
    > +
    > + return paddr >= swiotlb_start &&
    > + paddr < (swiotlb_start + (io_tlb_nslabs << IO_TLB_SHIFT));
    > }
    >
    > /*
    > @@ -938,6 +935,8 @@ EXPORT_SYMBOL(swiotlb_dma_mapping_error);
    > int
    > swiotlb_dma_supported(struct device *hwdev, u64 mask)
    > {
    > - return swiotlb_virt_to_bus(hwdev, io_tlb_end - 1) <= mask;
    > + unsigned long bytes = io_tlb_nslabs << IO_TLB_SHIFT;
    > +
    > + return swiotlb_virt_to_bus(hwdev, io_tlb_start + bytes - 1) <= mask;
    > }
    > EXPORT_SYMBOL(swiotlb_dma_supported);
    >
    > --
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