/*
 *  Copyright 2010
 *  by Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
 *
 * This code provides a IOMMU for Xen PV guests with PCI passthrough.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License v2.0 as published by
 * the Free Software Foundation
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * PV guests under Xen are running in an non-contiguous memory architecture.
 *
 * When PCI pass-through is utilized, this necessitates an IOMMU for
 * translating bus (DMA) to virtual and vice-versa and also providing a
 * mechanism to have contiguous pages for device drivers operations (say DMA
 * operations).
 *
 * Specifically, under Xen the Linux idea of pages is an illusion. It
 * assumes that pages start at zero and go up to the available memory. To
 * help with that, the Linux Xen MMU provides a lookup mechanism to
 * translate the page frame numbers (PFN) to machine frame numbers (MFN)
 * and vice-versa. The MFN are the "real" frame numbers. Furthermore
 * memory is not contiguous. Xen hypervisor stitches memory for guests
 * from different pools, which means there is no guarantee that PFN==MFN
 * and PFN+1==MFN+1. Lastly with Xen 4.0, pages (in debug mode) are
 * allocated in descending order (high to low), meaning the guest might
 * never get any MFN's under the 4GB mark.
 *
 */

#include <linux/bootmem.h>
#include <linux/dma-mapping.h>
#include <xen/swiotlb-xen.h>
#include <xen/page.h>
#include <xen/xen-ops.h>
/*
 * Used to do a quick range check in swiotlb_tbl_unmap_single and
 * swiotlb_tbl_sync_single_*, to see if the memory was in fact allocated by this
 * API.
 */

static char *xen_io_tlb_start, *xen_io_tlb_end;
static unsigned long xen_io_tlb_nslabs;
/*
 * Quick lookup value of the bus address of the IOTLB.
 */

u64 start_dma_addr;

static dma_addr_t xen_phys_to_bus(phys_addr_t paddr)
{
        return phys_to_machine(XPADDR(paddr)).maddr;;
}

static phys_addr_t xen_bus_to_phys(dma_addr_t baddr)
{
        return machine_to_phys(XMADDR(baddr)).paddr;
}

static dma_addr_t xen_virt_to_bus(void *address)
{
        return xen_phys_to_bus(virt_to_phys(address));
}

static int check_pages_physically_contiguous(unsigned long pfn,
                                             unsigned int offset,
                                             size_t length)
{
        unsigned long next_mfn;
        int i;
        int nr_pages;

        next_mfn = pfn_to_mfn(pfn);
        nr_pages = (offset + length + PAGE_SIZE-1) >> PAGE_SHIFT;

        for (i = 1; i < nr_pages; i++) {
                if (pfn_to_mfn(++pfn) != ++next_mfn)
                        return 0;
        }
        return 1;
}

static int range_straddles_page_boundary(phys_addr_t p, size_t size)
{
        unsigned long pfn = PFN_DOWN(p);
        unsigned int offset = p & ~PAGE_MASK;

        if (offset + size <= PAGE_SIZE)
                return 0;
        if (check_pages_physically_contiguous(pfn, offset, size))
                return 0;
        return 1;
}

static int is_xen_swiotlb_buffer(dma_addr_t dma_addr)
{
        unsigned long mfn = PFN_DOWN(dma_addr);
        unsigned long pfn = mfn_to_local_pfn(mfn);
        phys_addr_t paddr;

        /* If the address is outside our domain, it CAN
         * have the same virtual address as another address
         * in our domain. Therefore _only_ check address within our domain.
         */
        if (pfn_valid(pfn)) {
                paddr = PFN_PHYS(pfn);
                return paddr >= virt_to_phys(xen_io_tlb_start) &&
                       paddr < virt_to_phys(xen_io_tlb_end);
        }
        return 0;
}

static int max_dma_bits = 32;

static int
xen_swiotlb_fixup(void *buf, size_t size, unsigned long nslabs)
{
        int i, rc;
        int dma_bits;

        dma_bits = get_order(IO_TLB_SEGSIZE << IO_TLB_SHIFT) + PAGE_SHIFT;

        i = 0;
        do {
                int slabs = min(nslabs - i, (unsigned long)IO_TLB_SEGSIZE);

                do {
                        rc = xen_create_contiguous_region(
                                (unsigned long)buf + (i << IO_TLB_SHIFT),
                                get_order(slabs << IO_TLB_SHIFT),
                                dma_bits);
                } while (rc && dma_bits++ < max_dma_bits);
                if (rc)
                        return rc;

                i += slabs;
        } while (i < nslabs);
        return 0;
}

void __init xen_swiotlb_init(int verbose)
{
        unsigned long bytes;
        int rc;

        xen_io_tlb_nslabs = (64 * 1024 * 1024 >> IO_TLB_SHIFT);
        xen_io_tlb_nslabs = ALIGN(xen_io_tlb_nslabs, IO_TLB_SEGSIZE);

        bytes = xen_io_tlb_nslabs << IO_TLB_SHIFT;

        /*
         * Get IO TLB memory from any location.
         */
        xen_io_tlb_start = alloc_bootmem(bytes);
        if (!xen_io_tlb_start)
                panic("Cannot allocate SWIOTLB buffer");

        xen_io_tlb_end = xen_io_tlb_start + bytes;
        /*
         * And replace that memory with pages under 4GB.
         */
        rc = xen_swiotlb_fixup(xen_io_tlb_start,
                               bytes,
                               xen_io_tlb_nslabs);
        if (rc)
                goto error;

        start_dma_addr = xen_virt_to_bus(xen_io_tlb_start);
        swiotlb_init_with_tbl(xen_io_tlb_start, xen_io_tlb_nslabs, verbose);

        return;
error:
        panic("DMA(%d): Failed to exchange pages allocated for DMA with Xen! "\
              "We either don't have the permission or you do not have enough"\
              "free memory under 4GB!\n", rc);
}

void *
xen_swiotlb_alloc_coherent(struct device *hwdev, size_t size,
                           dma_addr_t *dma_handle, gfp_t flags)
{
        void *ret;
        int order = get_order(size);
        u64 dma_mask = DMA_BIT_MASK(32);
        unsigned long vstart;

        /*
        * Ignore region specifiers - the kernel's ideas of
        * pseudo-phys memory layout has nothing to do with the
        * machine physical layout.  We can't allocate highmem
        * because we can't return a pointer to it.
        */
        flags &= ~(__GFP_DMA | __GFP_HIGHMEM);

        if (dma_alloc_from_coherent(hwdev, size, dma_handle, &ret))
                return ret;

        vstart = __get_free_pages(flags, order);
        ret = (void *)vstart;

        if (hwdev && hwdev->coherent_dma_mask)
                dma_mask = dma_alloc_coherent_mask(hwdev, flags);

        if (ret) {
                if (xen_create_contiguous_region(vstart, order,
                                                 fls64(dma_mask)) != 0) {
                        free_pages(vstart, order);
                        return NULL;
                }
                memset(ret, 0, size);
                *dma_handle = virt_to_machine(ret).maddr;
        }
        return ret;
}
EXPORT_SYMBOL_GPL(xen_swiotlb_alloc_coherent);

void
xen_swiotlb_free_coherent(struct device *hwdev, size_t size, void *vaddr,
                          dma_addr_t dev_addr)
{
        int order = get_order(size);

        if (dma_release_from_coherent(hwdev, order, vaddr))
                return;

        xen_destroy_contiguous_region((unsigned long)vaddr, order);
        free_pages((unsigned long)vaddr, order);
}
EXPORT_SYMBOL_GPL(xen_swiotlb_free_coherent);


/*
 * Map a single buffer of the indicated size for DMA in streaming mode.  The
 * physical address to use is returned.
 *
 * Once the device is given the dma address, the device owns this memory until
 * either xen_swiotlb_unmap_page or xen_swiotlb_dma_sync_single is performed.
 */
dma_addr_t xen_swiotlb_map_page(struct device *dev, struct page *page,
                                unsigned long offset, size_t size,
                                enum dma_data_direction dir,
                                struct dma_attrs *attrs)
{
        phys_addr_t phys = page_to_phys(page) + offset;
        dma_addr_t dev_addr = xen_phys_to_bus(phys);
        void *map;

        BUG_ON(dir == DMA_NONE);
        /*
         * If the address happens to be in the device's DMA window,
         * we can safely return the device addr and not worry about bounce
         * buffering it.
         */
        if (dma_capable(dev, dev_addr, size) &&
            !range_straddles_page_boundary(phys, size) && !swiotlb_force)
                return dev_addr;

        /*
         * Oh well, have to allocate and map a bounce buffer.
         */
        map = swiotlb_tbl_map_single(dev, start_dma_addr, phys, size, dir);
        if (!map)
                return DMA_ERROR_CODE;

        dev_addr = xen_virt_to_bus(map);

        /*
         * Ensure that the address returned is DMA'ble
         */
        if (!dma_capable(dev, dev_addr, size))
                panic("map_single: bounce buffer is not DMA'ble");

        return dev_addr;
}
EXPORT_SYMBOL_GPL(xen_swiotlb_map_page);

/*
 * Unmap a single streaming mode DMA translation.  The dma_addr and size must
 * match what was provided for in a previous xen_swiotlb_map_page call.  All
 * other usages are undefined.
 *
 * After this call, reads by the cpu to the buffer are guaranteed to see
 * whatever the device wrote there.
 */
static void xen_unmap_single(struct device *hwdev, dma_addr_t dev_addr,
                             size_t size, enum dma_data_direction dir)
{
        phys_addr_t paddr = xen_bus_to_phys(dev_addr);

        BUG_ON(dir == DMA_NONE);

        /* NOTE: We use dev_addr here, not paddr! */
        if (is_xen_swiotlb_buffer(dev_addr)) {
                swiotlb_tbl_unmap_single(hwdev, phys_to_virt(paddr), size, dir);
                return;
        }

        if (dir != DMA_FROM_DEVICE)
                return;

        /*
         * phys_to_virt doesn't work with hihgmem page but we could
         * call dma_mark_clean() with hihgmem page here. However, we
         * are fine since dma_mark_clean() is null on POWERPC. We can
         * make dma_mark_clean() take a physical address if necessary.
         */
        dma_mark_clean(phys_to_virt(paddr), size);
}

void xen_swiotlb_unmap_page(struct device *hwdev, dma_addr_t dev_addr,
                            size_t size, enum dma_data_direction dir,
                            struct dma_attrs *attrs)
{
        xen_unmap_single(hwdev, dev_addr, size, dir);
}
EXPORT_SYMBOL_GPL(xen_swiotlb_unmap_page);

/*
 * Make physical memory consistent for a single streaming mode DMA translation
 * after a transfer.
 *
 * If you perform a xen_swiotlb_map_page() but wish to interrogate the buffer
 * using the cpu, yet do not wish to teardown the dma mapping, you must
 * call this function before doing so.  At the next point you give the dma
 * address back to the card, you must first perform a
 * xen_swiotlb_dma_sync_for_device, and then the device again owns the buffer
 */
static void
xen_swiotlb_sync_single(struct device *hwdev, dma_addr_t dev_addr,
                        size_t size, enum dma_data_direction dir,
                        enum dma_sync_target target)
{
        phys_addr_t paddr = xen_bus_to_phys(dev_addr);

        BUG_ON(dir == DMA_NONE);

        /* NOTE: We use dev_addr here, not paddr! */
        if (is_xen_swiotlb_buffer(dev_addr)) {
                swiotlb_tbl_sync_single(hwdev, phys_to_virt(paddr), size, dir,
                                       target);
                return;
        }

        if (dir != DMA_FROM_DEVICE)
                return;

        dma_mark_clean(phys_to_virt(paddr), size);
}

void
xen_swiotlb_sync_single_for_cpu(struct device *hwdev, dma_addr_t dev_addr,
                                size_t size, enum dma_data_direction dir)
{
        xen_swiotlb_sync_single(hwdev, dev_addr, size, dir, SYNC_FOR_CPU);
}
EXPORT_SYMBOL_GPL(xen_swiotlb_sync_single_for_cpu);

void
xen_swiotlb_sync_single_for_device(struct device *hwdev, dma_addr_t dev_addr,
                                   size_t size, enum dma_data_direction dir)
{
        xen_swiotlb_sync_single(hwdev, dev_addr, size, dir, SYNC_FOR_DEVICE);
}
EXPORT_SYMBOL_GPL(xen_swiotlb_sync_single_for_device);

/*
 * Map a set of buffers described by scatterlist in streaming mode for DMA.
 * This is the scatter-gather version of the above xen_swiotlb_map_page
 * interface.  Here the scatter gather list elements are each tagged with the
 * appropriate dma address and length.  They are obtained via
 * sg_dma_{address,length}(SG).
 *
 * NOTE: An implementation may be able to use a smaller number of
 *       DMA address/length pairs than there are SG table elements.
 *       (for example via virtual mapping capabilities)
 *       The routine returns the number of addr/length pairs actually
 *       used, at most nents.
 *
 * Device ownership issues as mentioned above for xen_swiotlb_map_page are the
 * same here.
 */
int
xen_swiotlb_map_sg_attrs(struct device *hwdev, struct scatterlist *sgl,
                         int nelems, enum dma_data_direction dir,
                         struct dma_attrs *attrs)
{
        struct scatterlist *sg;
        int i;

        BUG_ON(dir == DMA_NONE);

        for_each_sg(sgl, sg, nelems, i) {
                phys_addr_t paddr = sg_phys(sg);
                dma_addr_t dev_addr = xen_phys_to_bus(paddr);

                if (swiotlb_force ||
                    !dma_capable(hwdev, dev_addr, sg->length) ||
                    range_straddles_page_boundary(paddr, sg->length)) {
                        void *map = swiotlb_tbl_map_single(hwdev,
                                                           start_dma_addr,
                                                           sg_phys(sg),
                                                           sg->length, dir);
                        if (!map) {
                                /* Don't panic here, we expect map_sg users
                                   to do proper error handling. */
                                xen_swiotlb_unmap_sg_attrs(hwdev, sgl, i, dir,
                                                           attrs);
                                sgl[0].dma_length = 0;
                                return DMA_ERROR_CODE;
                        }
                        sg->dma_address = xen_virt_to_bus(map);
                } else
                        sg->dma_address = dev_addr;
                sg->dma_length = sg->length;
        }
        return nelems;
}
EXPORT_SYMBOL_GPL(xen_swiotlb_map_sg_attrs);

int
xen_swiotlb_map_sg(struct device *hwdev, struct scatterlist *sgl, int nelems,
                   enum dma_data_direction dir)
{
        return xen_swiotlb_map_sg_attrs(hwdev, sgl, nelems, dir, NULL);
}
EXPORT_SYMBOL_GPL(xen_swiotlb_map_sg);

/*
 * Unmap a set of streaming mode DMA translations.  Again, cpu read rules
 * concerning calls here are the same as for swiotlb_unmap_page() above.
 */
void
xen_swiotlb_unmap_sg_attrs(struct device *hwdev, struct scatterlist *sgl,
                           int nelems, enum dma_data_direction dir,
                           struct dma_attrs *attrs)
{
        struct scatterlist *sg;
        int i;

        BUG_ON(dir == DMA_NONE);

        for_each_sg(sgl, sg, nelems, i)
                xen_unmap_single(hwdev, sg->dma_address, sg->dma_length, dir);

}
EXPORT_SYMBOL_GPL(xen_swiotlb_unmap_sg_attrs);

void
xen_swiotlb_unmap_sg(struct device *hwdev, struct scatterlist *sgl, int nelems,
                     enum dma_data_direction dir)
{
        return xen_swiotlb_unmap_sg_attrs(hwdev, sgl, nelems, dir, NULL);
}
EXPORT_SYMBOL_GPL(xen_swiotlb_unmap_sg);

/*
 * Make physical memory consistent for a set of streaming mode DMA translations
 * after a transfer.
 *
 * The same as swiotlb_sync_single_* but for a scatter-gather list, same rules
 * and usage.
 */
static void
xen_swiotlb_sync_sg(struct device *hwdev, struct scatterlist *sgl,
                    int nelems, enum dma_data_direction dir,
                    enum dma_sync_target target)
{
        struct scatterlist *sg;
        int i;

        for_each_sg(sgl, sg, nelems, i)
                xen_swiotlb_sync_single(hwdev, sg->dma_address,
                                        sg->dma_length, dir, target);
}

void
xen_swiotlb_sync_sg_for_cpu(struct device *hwdev, struct scatterlist *sg,
                            int nelems, enum dma_data_direction dir)
{
        xen_swiotlb_sync_sg(hwdev, sg, nelems, dir, SYNC_FOR_CPU);
}
EXPORT_SYMBOL_GPL(xen_swiotlb_sync_sg_for_cpu);

void
xen_swiotlb_sync_sg_for_device(struct device *hwdev, struct scatterlist *sg,
                               int nelems, enum dma_data_direction dir)
{
        xen_swiotlb_sync_sg(hwdev, sg, nelems, dir, SYNC_FOR_DEVICE);
}
EXPORT_SYMBOL_GPL(xen_swiotlb_sync_sg_for_device);

int
xen_swiotlb_dma_mapping_error(struct device *hwdev, dma_addr_t dma_addr)
{
        return !dma_addr;
}
EXPORT_SYMBOL_GPL(xen_swiotlb_dma_mapping_error);

/*
 * Return whether the given device DMA address mask can be supported
 * properly.  For example, if your device can only drive the low 24-bits
 * during bus mastering, then you would pass 0x00ffffff as the mask to
 * this function.
 */
int
xen_swiotlb_dma_supported(struct device *hwdev, u64 mask)
{
        return xen_virt_to_bus(xen_io_tlb_end - 1) <= mask;
}
EXPORT_SYMBOL_GPL(xen_swiotlb_dma_supported);