// SPDX-License-Identifier: GPL-2.0-only
/*
 * Dynamic DMA mapping support for AMD Hammer.
 *
 * Use the integrated AGP GART in the Hammer northbridge as an IOMMU for PCI.
 * This allows to use PCI devices that only support 32bit addresses on systems
 * with more than 4GB.
 *
 * See Documentation/core-api/dma-api-howto.rst for the interface specification.
 *
 * Copyright 2002 Andi Kleen, SuSE Labs.
 */

#include <linux/types.h>
#include <linux/ctype.h>
#include <linux/agp_backend.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/sched/debug.h>
#include <linux/string.h>
#include <linux/spinlock.h>
#include <linux/pci.h>
#include <linux/topology.h>
#include <linux/interrupt.h>
#include <linux/bitmap.h>
#include <linux/kdebug.h>
#include <linux/scatterlist.h>
#include <linux/iommu-helper.h>
#include <linux/syscore_ops.h>
#include <linux/io.h>
#include <linux/gfp.h>
#include <linux/atomic.h>
#include <linux/dma-direct.h>
#include <asm/mtrr.h>
#include <asm/proto.h>
#include <asm/iommu.h>
#include <asm/gart.h>
#include <asm/set_memory.h>
#include <asm/swiotlb.h>
#include <asm/dma.h>
#include <asm/amd_nb.h>
#include <asm/x86_init.h>
#include <asm/iommu_table.h>

static unsigned long iommu_bus_base;    /* GART remapping area (physical) */
static unsigned long iommu_size;        /* size of remapping area bytes */
static unsigned long iommu_pages;       /* .. and in pages */

static u32 *iommu_gatt_base;            /* Remapping table */

/*
 * If this is disabled the IOMMU will use an optimized flushing strategy
 * of only flushing when an mapping is reused. With it true the GART is
 * flushed for every mapping. Problem is that doing the lazy flush seems
 * to trigger bugs with some popular PCI cards, in particular 3ware (but
 * has been also also seen with Qlogic at least).
 */
static int iommu_fullflush = 1;

/* Allocation bitmap for the remapping area: */
static DEFINE_SPINLOCK(iommu_bitmap_lock);
/* Guarded by iommu_bitmap_lock: */
static unsigned long *iommu_gart_bitmap;

static u32 gart_unmapped_entry;

#define GPTE_VALID    1
#define GPTE_COHERENT 2
#define GPTE_ENCODE(x) \
        (((x) & 0xfffff000) | (((x) >> 32) << 4) | GPTE_VALID | GPTE_COHERENT)
#define GPTE_DECODE(x) (((x) & 0xfffff000) | (((u64)(x) & 0xff0) << 28))

#ifdef CONFIG_AGP
#define AGPEXTERN extern
#else
#define AGPEXTERN
#endif

/* GART can only remap to physical addresses < 1TB */
#define GART_MAX_PHYS_ADDR      (1ULL << 40)

/* backdoor interface to AGP driver */
AGPEXTERN int agp_memory_reserved;
AGPEXTERN __u32 *agp_gatt_table;

static unsigned long next_bit;  /* protected by iommu_bitmap_lock */
static bool need_flush;         /* global flush state. set for each gart wrap */

static unsigned long alloc_iommu(struct device *dev, int size,
                                 unsigned long align_mask)
{
        unsigned long offset, flags;
        unsigned long boundary_size;
        unsigned long base_index;

        base_index = ALIGN(iommu_bus_base & dma_get_seg_boundary(dev),
                           PAGE_SIZE) >> PAGE_SHIFT;
        boundary_size = ALIGN((u64)dma_get_seg_boundary(dev) + 1,
                              PAGE_SIZE) >> PAGE_SHIFT;

        spin_lock_irqsave(&iommu_bitmap_lock, flags);
        offset = iommu_area_alloc(iommu_gart_bitmap, iommu_pages, next_bit,
                                  size, base_index, boundary_size, align_mask);
        if (offset == -1) {
                need_flush = true;
                offset = iommu_area_alloc(iommu_gart_bitmap, iommu_pages, 0,
                                          size, base_index, boundary_size,
                                          align_mask);
        }
        if (offset != -1) {
                next_bit = offset+size;
                if (next_bit >= iommu_pages) {
                        next_bit = 0;
                        need_flush = true;
                }
        }
        if (iommu_fullflush)
                need_flush = true;
        spin_unlock_irqrestore(&iommu_bitmap_lock, flags);

        return offset;
}

static void free_iommu(unsigned long offset, int size)
{
        unsigned long flags;

        spin_lock_irqsave(&iommu_bitmap_lock, flags);
        bitmap_clear(iommu_gart_bitmap, offset, size);
        if (offset >= next_bit)
                next_bit = offset + size;
        spin_unlock_irqrestore(&iommu_bitmap_lock, flags);
}

/*
 * Use global flush state to avoid races with multiple flushers.
 */
static void flush_gart(void)
{
        unsigned long flags;

        spin_lock_irqsave(&iommu_bitmap_lock, flags);
        if (need_flush) {
                amd_flush_garts();
                need_flush = false;
        }
        spin_unlock_irqrestore(&iommu_bitmap_lock, flags);
}

#ifdef CONFIG_IOMMU_LEAK
/* Debugging aid for drivers that don't free their IOMMU tables */
static void dump_leak(void)
{
        static int dump;

        if (dump)
                return;
        dump = 1;

        show_stack(NULL, NULL, KERN_ERR);
        debug_dma_dump_mappings(NULL);
}
#endif

static void iommu_full(struct device *dev, size_t size, int dir)
{
        /*
         * Ran out of IOMMU space for this operation. This is very bad.
         * Unfortunately the drivers cannot handle this operation properly.
         * Return some non mapped prereserved space in the aperture and
         * let the Northbridge deal with it. This will result in garbage
         * in the IO operation. When the size exceeds the prereserved space
         * memory corruption will occur or random memory will be DMAed
         * out. Hopefully no network devices use single mappings that big.
         */

        dev_err(dev, "PCI-DMA: Out of IOMMU space for %lu bytes\n", size);
#ifdef CONFIG_IOMMU_LEAK
        dump_leak();
#endif
}

static inline int
need_iommu(struct device *dev, unsigned long addr, size_t size)
{
        return force_iommu || !dma_capable(dev, addr, size, true);
}

static inline int
nonforced_iommu(struct device *dev, unsigned long addr, size_t size)
{
        return !dma_capable(dev, addr, size, true);
}

/* Map a single continuous physical area into the IOMMU.
 * Caller needs to check if the iommu is needed and flush.
 */
static dma_addr_t dma_map_area(struct device *dev, dma_addr_t phys_mem,
                                size_t size, int dir, unsigned long align_mask)
{
        unsigned long npages = iommu_num_pages(phys_mem, size, PAGE_SIZE);
        unsigned long iommu_page;
        int i;

        if (unlikely(phys_mem + size > GART_MAX_PHYS_ADDR))
                return DMA_MAPPING_ERROR;

        iommu_page = alloc_iommu(dev, npages, align_mask);
        if (iommu_page == -1) {
                if (!nonforced_iommu(dev, phys_mem, size))
                        return phys_mem;
                if (panic_on_overflow)
                        panic("dma_map_area overflow %lu bytes\n", size);
                iommu_full(dev, size, dir);
                return DMA_MAPPING_ERROR;
        }

        for (i = 0; i < npages; i++) {
                iommu_gatt_base[iommu_page + i] = GPTE_ENCODE(phys_mem);
                phys_mem += PAGE_SIZE;
        }
        return iommu_bus_base + iommu_page*PAGE_SIZE + (phys_mem & ~PAGE_MASK);
}

/* Map a single area into the IOMMU */
static dma_addr_t gart_map_page(struct device *dev, struct page *page,
                                unsigned long offset, size_t size,
                                enum dma_data_direction dir,
                                unsigned long attrs)
{
        unsigned long bus;
        phys_addr_t paddr = page_to_phys(page) + offset;

        if (!need_iommu(dev, paddr, size))
                return paddr;

        bus = dma_map_area(dev, paddr, size, dir, 0);
        flush_gart();

        return bus;
}

/*
 * Free a DMA mapping.
 */
static void gart_unmap_page(struct device *dev, dma_addr_t dma_addr,
                            size_t size, enum dma_data_direction dir,
                            unsigned long attrs)
{
        unsigned long iommu_page;
        int npages;
        int i;

        if (WARN_ON_ONCE(dma_addr == DMA_MAPPING_ERROR))
                return;

        /*
         * This driver will not always use a GART mapping, but might have
         * created a direct mapping instead.  If that is the case there is
         * nothing to unmap here.
         */
        if (dma_addr < iommu_bus_base ||
            dma_addr >= iommu_bus_base + iommu_size)
                return;

        iommu_page = (dma_addr - iommu_bus_base)>>PAGE_SHIFT;
        npages = iommu_num_pages(dma_addr, size, PAGE_SIZE);
        for (i = 0; i < npages; i++) {
                iommu_gatt_base[iommu_page + i] = gart_unmapped_entry;
        }
        free_iommu(iommu_page, npages);
}

/*
 * Wrapper for pci_unmap_single working with scatterlists.
 */
static void gart_unmap_sg(struct device *dev, struct scatterlist *sg, int nents,
                          enum dma_data_direction dir, unsigned long attrs)
{
        struct scatterlist *s;
        int i;

        for_each_sg(sg, s, nents, i) {
                if (!s->dma_length || !s->length)
                        break;
                gart_unmap_page(dev, s->dma_address, s->dma_length, dir, 0);
        }
}

/* Fallback for dma_map_sg in case of overflow */
static int dma_map_sg_nonforce(struct device *dev, struct scatterlist *sg,
                               int nents, int dir)
{
        struct scatterlist *s;
        int i;

#ifdef CONFIG_IOMMU_DEBUG
        pr_debug("dma_map_sg overflow\n");
#endif

        for_each_sg(sg, s, nents, i) {
                unsigned long addr = sg_phys(s);

                if (nonforced_iommu(dev, addr, s->length)) {
                        addr = dma_map_area(dev, addr, s->length, dir, 0);
                        if (addr == DMA_MAPPING_ERROR) {
                                if (i > 0)
                                        gart_unmap_sg(dev, sg, i, dir, 0);
                                nents = 0;
                                sg[0].dma_length = 0;
                                break;
                        }
                }
                s->dma_address = addr;
                s->dma_length = s->length;
        }
        flush_gart();

        return nents;
}

/* Map multiple scatterlist entries continuous into the first. */
static int __dma_map_cont(struct device *dev, struct scatterlist *start,
                          int nelems, struct scatterlist *sout,
                          unsigned long pages)
{
        unsigned long iommu_start = alloc_iommu(dev, pages, 0);
        unsigned long iommu_page = iommu_start;
        struct scatterlist *s;
        int i;

        if (iommu_start == -1)
                return -1;

        for_each_sg(start, s, nelems, i) {
                unsigned long pages, addr;
                unsigned long phys_addr = s->dma_address;

                BUG_ON(s != start && s->offset);
                if (s == start) {
                        sout->dma_address = iommu_bus_base;
                        sout->dma_address += iommu_page*PAGE_SIZE + s->offset;
                        sout->dma_length = s->length;
                } else {
                        sout->dma_length += s->length;
                }

                addr = phys_addr;
                pages = iommu_num_pages(s->offset, s->length, PAGE_SIZE);
                while (pages--) {
                        iommu_gatt_base[iommu_page] = GPTE_ENCODE(addr);
                        addr += PAGE_SIZE;
                        iommu_page++;
                }
        }
        BUG_ON(iommu_page - iommu_start != pages);

        return 0;
}

static inline int
dma_map_cont(struct device *dev, struct scatterlist *start, int nelems,
             struct scatterlist *sout, unsigned long pages, int need)
{
        if (!need) {
                BUG_ON(nelems != 1);
                sout->dma_address = start->dma_address;
                sout->dma_length = start->length;
                return 0;
        }
        return __dma_map_cont(dev, start, nelems, sout, pages);
}

/*
 * DMA map all entries in a scatterlist.
 * Merge chunks that have page aligned sizes into a continuous mapping.
 */
static int gart_map_sg(struct device *dev, struct scatterlist *sg, int nents,
                       enum dma_data_direction dir, unsigned long attrs)
{
        struct scatterlist *s, *ps, *start_sg, *sgmap;
        int need = 0, nextneed, i, out, start;
        unsigned long pages = 0;
        unsigned int seg_size;
        unsigned int max_seg_size;

        if (nents == 0)
                return 0;

        out             = 0;
        start           = 0;
        start_sg        = sg;
        sgmap           = sg;
        seg_size        = 0;
        max_seg_size    = dma_get_max_seg_size(dev);
        ps              = NULL; /* shut up gcc */

        for_each_sg(sg, s, nents, i) {
                dma_addr_t addr = sg_phys(s);

                s->dma_address = addr;
                BUG_ON(s->length == 0);

                nextneed = need_iommu(dev, addr, s->length);

                /* Handle the previous not yet processed entries */
                if (i > start) {
                        /*
                         * Can only merge when the last chunk ends on a
                         * page boundary and the new one doesn't have an
                         * offset.
                         */
                        if (!iommu_merge || !nextneed || !need || s->offset ||
                            (s->length + seg_size > max_seg_size) ||
                            (ps->offset + ps->length) % PAGE_SIZE) {
                                if (dma_map_cont(dev, start_sg, i - start,
                                                 sgmap, pages, need) < 0)
                                        goto error;
                                out++;

                                seg_size        = 0;
                                sgmap           = sg_next(sgmap);
                                pages           = 0;
                                start           = i;
                                start_sg        = s;
                        }
                }

                seg_size += s->length;
                need = nextneed;
                pages += iommu_num_pages(s->offset, s->length, PAGE_SIZE);
                ps = s;
        }
        if (dma_map_cont(dev, start_sg, i - start, sgmap, pages, need) < 0)
                goto error;
        out++;
        flush_gart();
        if (out < nents) {
                sgmap = sg_next(sgmap);
                sgmap->dma_length = 0;
        }
        return out;

error:
        flush_gart();
        gart_unmap_sg(dev, sg, out, dir, 0);

        /* When it was forced or merged try again in a dumb way */
        if (force_iommu || iommu_merge) {
                out = dma_map_sg_nonforce(dev, sg, nents, dir);
                if (out > 0)
                        return out;
        }
        if (panic_on_overflow)
                panic("dma_map_sg: overflow on %lu pages\n", pages);

        iommu_full(dev, pages << PAGE_SHIFT, dir);
        for_each_sg(sg, s, nents, i)
                s->dma_address = DMA_MAPPING_ERROR;
        return 0;
}

/* allocate and map a coherent mapping */
static void *
gart_alloc_coherent(struct device *dev, size_t size, dma_addr_t *dma_addr,
                    gfp_t flag, unsigned long attrs)
{
        void *vaddr;

        vaddr = dma_direct_alloc_pages(dev, size, dma_addr, flag, attrs);
        if (!vaddr ||
            !force_iommu || dev->coherent_dma_mask <= DMA_BIT_MASK(24))
                return vaddr;

        *dma_addr = dma_map_area(dev, virt_to_phys(vaddr), size,
                        DMA_BIDIRECTIONAL, (1UL << get_order(size)) - 1);
        flush_gart();
        if (unlikely(*dma_addr == DMA_MAPPING_ERROR))
                goto out_free;
        return vaddr;
out_free:
        dma_direct_free_pages(dev, size, vaddr, *dma_addr, attrs);
        return NULL;
}

/* free a coherent mapping */
static void
gart_free_coherent(struct device *dev, size_t size, void *vaddr,
                   dma_addr_t dma_addr, unsigned long attrs)
{
        gart_unmap_page(dev, dma_addr, size, DMA_BIDIRECTIONAL, 0);
        dma_direct_free_pages(dev, size, vaddr, dma_addr, attrs);
}

static int no_agp;

static __init unsigned long check_iommu_size(unsigned long aper, u64 aper_size)
{
        unsigned long a;

        if (!iommu_size) {
                iommu_size = aper_size;
                if (!no_agp)
                        iommu_size /= 2;
        }

        a = aper + iommu_size;
        iommu_size -= round_up(a, PMD_PAGE_SIZE) - a;

        if (iommu_size < 64*1024*1024) {
                pr_warn("PCI-DMA: Warning: Small IOMMU %luMB."
                        " Consider increasing the AGP aperture in BIOS\n",
                        iommu_size >> 20);
        }

        return iommu_size;
}

static __init unsigned read_aperture(struct pci_dev *dev, u32 *size)
{
        unsigned aper_size = 0, aper_base_32, aper_order;
        u64 aper_base;

        pci_read_config_dword(dev, AMD64_GARTAPERTUREBASE, &aper_base_32);
        pci_read_config_dword(dev, AMD64_GARTAPERTURECTL, &aper_order);
        aper_order = (aper_order >> 1) & 7;

        aper_base = aper_base_32 & 0x7fff;
        aper_base <<= 25;

        aper_size = (32 * 1024 * 1024) << aper_order;
        if (aper_base + aper_size > 0x100000000UL || !aper_size)
                aper_base = 0;

        *size = aper_size;
        return aper_base;
}

static void enable_gart_translations(void)
{
        int i;

        if (!amd_nb_has_feature(AMD_NB_GART))
                return;

        for (i = 0; i < amd_nb_num(); i++) {
                struct pci_dev *dev = node_to_amd_nb(i)->misc;

                enable_gart_translation(dev, __pa(agp_gatt_table));
        }

        /* Flush the GART-TLB to remove stale entries */
        amd_flush_garts();
}

/*
 * If fix_up_north_bridges is set, the north bridges have to be fixed up on
 * resume in the same way as they are handled in gart_iommu_hole_init().
 */
static bool fix_up_north_bridges;
static u32 aperture_order;
static u32 aperture_alloc;

void set_up_gart_resume(u32 aper_order, u32 aper_alloc)
{
        fix_up_north_bridges = true;
        aperture_order = aper_order;
        aperture_alloc = aper_alloc;
}

static void gart_fixup_northbridges(void)
{
        int i;

        if (!fix_up_north_bridges)
                return;

        if (!amd_nb_has_feature(AMD_NB_GART))
                return;

        pr_info("PCI-DMA: Restoring GART aperture settings\n");

        for (i = 0; i < amd_nb_num(); i++) {
                struct pci_dev *dev = node_to_amd_nb(i)->misc;

                /*
                 * Don't enable translations just yet.  That is the next
                 * step.  Restore the pre-suspend aperture settings.
                 */
                gart_set_size_and_enable(dev, aperture_order);
                pci_write_config_dword(dev, AMD64_GARTAPERTUREBASE, aperture_alloc >> 25);
        }
}

static void gart_resume(void)
{
        pr_info("PCI-DMA: Resuming GART IOMMU\n");

        gart_fixup_northbridges();

        enable_gart_translations();
}

static struct syscore_ops gart_syscore_ops = {
        .resume         = gart_resume,

};

/*
 * Private Northbridge GATT initialization in case we cannot use the
 * AGP driver for some reason.
 */
static __init int init_amd_gatt(struct agp_kern_info *info)
{
        unsigned aper_size, gatt_size, new_aper_size;
        unsigned aper_base, new_aper_base;
        struct pci_dev *dev;
        void *gatt;
        int i;

        pr_info("PCI-DMA: Disabling AGP.\n");

        aper_size = aper_base = info->aper_size = 0;
        dev = NULL;
        for (i = 0; i < amd_nb_num(); i++) {
                dev = node_to_amd_nb(i)->misc;
                new_aper_base = read_aperture(dev, &new_aper_size);
                if (!new_aper_base)
                        goto nommu;

                if (!aper_base) {
                        aper_size = new_aper_size;
                        aper_base = new_aper_base;
                }
                if (aper_size != new_aper_size || aper_base != new_aper_base)
                        goto nommu;
        }
        if (!aper_base)
                goto nommu;

        info->aper_base = aper_base;
        info->aper_size = aper_size >> 20;

        gatt_size = (aper_size >> PAGE_SHIFT) * sizeof(u32);
        gatt = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO,
                                        get_order(gatt_size));
        if (!gatt)
                panic("Cannot allocate GATT table");
        if (set_memory_uc((unsigned long)gatt, gatt_size >> PAGE_SHIFT))
                panic("Could not set GART PTEs to uncacheable pages");

        agp_gatt_table = gatt;

        register_syscore_ops(&gart_syscore_ops);

        flush_gart();

        pr_info("PCI-DMA: aperture base @ %x size %u KB\n",
               aper_base, aper_size>>10);

        return 0;

 nommu:
        /* Should not happen anymore */
        pr_warn("PCI-DMA: More than 4GB of RAM and no IOMMU - falling back to iommu=soft.\n");
        return -1;
}

static const struct dma_map_ops gart_dma_ops = {
        .map_sg                         = gart_map_sg,
        .unmap_sg                       = gart_unmap_sg,
        .map_page                       = gart_map_page,
        .unmap_page                     = gart_unmap_page,
        .alloc                          = gart_alloc_coherent,
        .free                           = gart_free_coherent,
        .mmap                           = dma_common_mmap,
        .get_sgtable                    = dma_common_get_sgtable,
        .dma_supported                  = dma_direct_supported,
        .get_required_mask              = dma_direct_get_required_mask,
};

static void gart_iommu_shutdown(void)
{
        struct pci_dev *dev;
        int i;

        /* don't shutdown it if there is AGP installed */
        if (!no_agp)
                return;

        if (!amd_nb_has_feature(AMD_NB_GART))
                return;

        for (i = 0; i < amd_nb_num(); i++) {
                u32 ctl;

                dev = node_to_amd_nb(i)->misc;
                pci_read_config_dword(dev, AMD64_GARTAPERTURECTL, &ctl);

                ctl &= ~GARTEN;

                pci_write_config_dword(dev, AMD64_GARTAPERTURECTL, ctl);
        }
}

int __init gart_iommu_init(void)
{
        struct agp_kern_info info;
        unsigned long iommu_start;
        unsigned long aper_base, aper_size;
        unsigned long start_pfn, end_pfn;
        unsigned long scratch;

        if (!amd_nb_has_feature(AMD_NB_GART))
                return 0;

#ifndef CONFIG_AGP_AMD64
        no_agp = 1;
#else
        /* Makefile puts PCI initialization via subsys_initcall first. */
        /* Add other AMD AGP bridge drivers here */
        no_agp = no_agp ||
                (agp_amd64_init() < 0) ||
                (agp_copy_info(agp_bridge, &info) < 0);
#endif

        if (no_iommu ||
            (!force_iommu && max_pfn <= MAX_DMA32_PFN) ||
            !gart_iommu_aperture ||
            (no_agp && init_amd_gatt(&info) < 0)) {
                if (max_pfn > MAX_DMA32_PFN) {
                        pr_warn("More than 4GB of memory but GART IOMMU not available.\n");
                        pr_warn("falling back to iommu=soft.\n");
                }
                return 0;
        }

        /* need to map that range */
        aper_size       = info.aper_size << 20;
        aper_base       = info.aper_base;
        end_pfn         = (aper_base>>PAGE_SHIFT) + (aper_size>>PAGE_SHIFT);

        start_pfn = PFN_DOWN(aper_base);
        if (!pfn_range_is_mapped(start_pfn, end_pfn))
                init_memory_mapping(start_pfn<<PAGE_SHIFT, end_pfn<<PAGE_SHIFT,
                                    PAGE_KERNEL);

        pr_info("PCI-DMA: using GART IOMMU.\n");
        iommu_size = check_iommu_size(info.aper_base, aper_size);
        iommu_pages = iommu_size >> PAGE_SHIFT;

        iommu_gart_bitmap = (void *) __get_free_pages(GFP_KERNEL | __GFP_ZERO,
                                                      get_order(iommu_pages/8));
        if (!iommu_gart_bitmap)
                panic("Cannot allocate iommu bitmap\n");

        pr_info("PCI-DMA: Reserving %luMB of IOMMU area in the AGP aperture\n",
               iommu_size >> 20);

        agp_memory_reserved     = iommu_size;
        iommu_start             = aper_size - iommu_size;
        iommu_bus_base          = info.aper_base + iommu_start;
        iommu_gatt_base         = agp_gatt_table + (iommu_start>>PAGE_SHIFT);

        /*
         * Unmap the IOMMU part of the GART. The alias of the page is
         * always mapped with cache enabled and there is no full cache
         * coherency across the GART remapping. The unmapping avoids
         * automatic prefetches from the CPU allocating cache lines in
         * there. All CPU accesses are done via the direct mapping to
         * the backing memory. The GART address is only used by PCI
         * devices.
         */
        set_memory_np((unsigned long)__va(iommu_bus_base),
                                iommu_size >> PAGE_SHIFT);
        /*
         * Tricky. The GART table remaps the physical memory range,
         * so the CPU wont notice potential aliases and if the memory
         * is remapped to UC later on, we might surprise the PCI devices
         * with a stray writeout of a cacheline. So play it sure and
         * do an explicit, full-scale wbinvd() _after_ having marked all
         * the pages as Not-Present:
         */
        wbinvd();

        /*
         * Now all caches are flushed and we can safely enable
         * GART hardware.  Doing it early leaves the possibility
         * of stale cache entries that can lead to GART PTE
         * errors.
         */
        enable_gart_translations();

        /*
         * Try to workaround a bug (thanks to BenH):
         * Set unmapped entries to a scratch page instead of 0.
         * Any prefetches that hit unmapped entries won't get an bus abort
         * then. (P2P bridge may be prefetching on DMA reads).
         */
        scratch = get_zeroed_page(GFP_KERNEL);
        if (!scratch)
                panic("Cannot allocate iommu scratch page");
        gart_unmapped_entry = GPTE_ENCODE(__pa(scratch));

        flush_gart();
        dma_ops = &gart_dma_ops;
        x86_platform.iommu_shutdown = gart_iommu_shutdown;
        swiotlb = 0;

        return 0;
}

void __init gart_parse_options(char *p)
{
        int arg;

        if (isdigit(*p) && get_option(&p, &arg))
                iommu_size = arg;
        if (!strncmp(p, "fullflush", 9))
                iommu_fullflush = 1;
        if (!strncmp(p, "nofullflush", 11))
                iommu_fullflush = 0;
        if (!strncmp(p, "noagp", 5))
                no_agp = 1;
        if (!strncmp(p, "noaperture", 10))
                fix_aperture = 0;
        /* duplicated from pci-dma.c */
        if (!strncmp(p, "force", 5))
                gart_iommu_aperture_allowed = 1;
        if (!strncmp(p, "allowed", 7))
                gart_iommu_aperture_allowed = 1;
        if (!strncmp(p, "memaper", 7)) {
                fallback_aper_force = 1;
                p += 7;
                if (*p == '=') {
                        ++p;
                        if (get_option(&p, &arg))
                                fallback_aper_order = arg;
                }
        }
}
IOMMU_INIT_POST(gart_iommu_hole_init);