arch/x86/kernel/pci-gart_64.c

/*
 * 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/DMA-mapping.txt for the interface specification.
 *
 * Copyright 2002 Andi Kleen, SuSE Labs.
 * Subject to the GNU General Public License v2 only.
 */

#include <linux/types.h>
#include <linux/ctype.h>
#include <linux/agp_backend.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <linux/string.h>
#include <linux/spinlock.h>
#include <linux/pci.h>
#include <linux/module.h>
#include <linux/topology.h>
#include <linux/interrupt.h>
#include <linux/bitops.h>
#include <linux/kdebug.h>
#include <linux/scatterlist.h>
#include <asm/atomic.h>
#include <asm/io.h>
#include <asm/mtrr.h>
#include <asm/pgtable.h>
#include <asm/proto.h>
#include <asm/gart.h>
#include <asm/cacheflush.h>
#include <asm/swiotlb.h>
#include <asm/dma.h>
#include <asm/k8.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).
 */
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))

#define to_pages(addr, size) \
	(round_up(((addr) & ~PAGE_MASK) + (size), PAGE_SIZE) >> PAGE_SHIFT)

#define EMERGENCY_PAGES 32 /* = 128KB */

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

/* 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 int need_flush;		/* global flush state. set for each gart wrap */

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

	spin_lock_irqsave(&iommu_bitmap_lock, flags);
	offset = find_next_zero_string(iommu_gart_bitmap, next_bit,
					iommu_pages, size);
	if (offset == -1) {
		need_flush = 1;
		offset = find_next_zero_string(iommu_gart_bitmap, 0,
						iommu_pages, size);
	}
	if (offset != -1) {
		set_bit_string(iommu_gart_bitmap, offset, size);
		next_bit = offset+size;
		if (next_bit >= iommu_pages) {
			next_bit = 0;
			need_flush = 1;
		}
	}
	if (iommu_fullflush)
		need_flush = 1;
	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);
	__clear_bit_string(iommu_gart_bitmap, 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) {
		k8_flush_garts();
		need_flush = 0;
	}
	spin_unlock_irqrestore(&iommu_bitmap_lock, flags);
}

#ifdef CONFIG_IOMMU_LEAK

#define SET_LEAK(x)							\
	do {								\
		if (iommu_leak_tab)					\
			iommu_leak_tab[x] = __builtin_return_address(0);\
	} while (0)

#define CLEAR_LEAK(x)							\
	do {								\
		if (iommu_leak_tab)					\
			iommu_leak_tab[x] = NULL;			\
	} while (0)

/* Debugging aid for drivers that don't free their IOMMU tables */
static void **iommu_leak_tab;
static int leak_trace;
static int iommu_leak_pages = 20;

static void dump_leak(void)
{
	int i;
	static int dump;

	if (dump || !iommu_leak_tab)
		return;
	dump = 1;
	show_stack(NULL, NULL);

	/* Very crude. dump some from the end of the table too */
	printk(KERN_DEBUG "Dumping %d pages from end of IOMMU:\n",
	       iommu_leak_pages);
	for (i = 0; i < iommu_leak_pages; i += 2) {
		printk(KERN_DEBUG "%lu: ", iommu_pages-i);
		printk_address((unsigned long) iommu_leak_tab[iommu_pages-i], 0);
		printk(KERN_CONT "%c", (i+1)%2 == 0 ? '\n' : ' ');
	}
	printk(KERN_DEBUG "\n");
}
#else
# define SET_LEAK(x)
# define CLEAR_LEAK(x)
#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.
	 */

	printk(KERN_ERR
		"PCI-DMA: Out of IOMMU space for %lu bytes at device %s\n",
		size, dev->bus_id);

	if (size > PAGE_SIZE*EMERGENCY_PAGES) {
		if (dir == PCI_DMA_FROMDEVICE || dir == PCI_DMA_BIDIRECTIONAL)
			panic("PCI-DMA: Memory would be corrupted\n");
		if (dir == PCI_DMA_TODEVICE || dir == PCI_DMA_BIDIRECTIONAL)
			panic(KERN_ERR
				"PCI-DMA: Random memory would be DMAed\n");
	}
#ifdef CONFIG_IOMMU_LEAK
	dump_leak();
#endif
}

static inline int
need_iommu(struct device *dev, unsigned long addr, size_t size)
{
	u64 mask = *dev->dma_mask;
	int high = addr + size > mask;
	int mmu = high;

	if (force_iommu)
		mmu = 1;

	return mmu;
}

static inline int
nonforced_iommu(struct device *dev, unsigned long addr, size_t size)
{
	u64 mask = *dev->dma_mask;
	int high = addr + size > mask;
	int mmu = high;

	return mmu;
}

/* 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 npages = to_pages(phys_mem, size);
	unsigned long iommu_page = alloc_iommu(npages);
	int i;

	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 bad_dma_address;
	}

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

static dma_addr_t
gart_map_simple(struct device *dev, char *buf, size_t size, int dir)
{
	dma_addr_t map = dma_map_area(dev, virt_to_bus(buf), size, dir);

	flush_gart();

	return map;
}

/* Map a single area into the IOMMU */
static dma_addr_t
gart_map_single(struct device *dev, void *addr, size_t size, int dir)
{
	unsigned long phys_mem, bus;

	if (!dev)
		dev = &fallback_dev;

	phys_mem = virt_to_phys(addr);
	if (!need_iommu(dev, phys_mem, size))
		return phys_mem;

	bus = gart_map_simple(dev, addr, size, dir);

	return bus;
}

/*
 * Free a DMA mapping.
 */
static void gart_unmap_single(struct device *dev, dma_addr_t dma_addr,
			      size_t size, int direction)
{
	unsigned long iommu_page;
	int npages;
	int i;

	if (dma_addr < iommu_bus_base + EMERGENCY_PAGES*PAGE_SIZE ||
	    dma_addr >= iommu_bus_base + iommu_size)
		return;

	iommu_page = (dma_addr - iommu_bus_base)>>PAGE_SHIFT;
	npages = to_pages(dma_addr, size);
	for (i = 0; i < npages; i++) {
		iommu_gatt_base[iommu_page + i] = gart_unmapped_entry;
		CLEAR_LEAK(iommu_page + i);
	}
	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, int dir)
{
	struct scatterlist *s;
	int i;

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

/* 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
	printk(KERN_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);
			if (addr == bad_dma_address) {
				if (i > 0)
					gart_unmap_sg(dev, sg, i, dir);
				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 scatterlist *start, int nelems,
			  struct scatterlist *sout, unsigned long pages)
{
	unsigned long iommu_start = alloc_iommu(pages);
	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 = to_pages(s->offset, s->length);
		while (pages--) {
			iommu_gatt_base[iommu_page] = GPTE_ENCODE(addr);
			SET_LEAK(iommu_page);
			addr += PAGE_SIZE;
			iommu_page++;
		}
	}
	BUG_ON(iommu_page - iommu_start != pages);

	return 0;
}

static inline int
dma_map_cont(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(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, int dir)
{
	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;

	if (!dev)
		dev = &fallback_dev;

	out = 0;
	start = 0;
	start_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(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 += to_pages(s->offset, s->length);
		ps = s;
	}
	if (dma_map_cont(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);

	/* 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 = bad_dma_address;
	return 0;
}

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) {
		printk(KERN_WARNING
			"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, 0x94, &aper_base_32);
	pci_read_config_dword(dev, 0x90, &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;
}

/*
 * Private Northbridge GATT initialization in case we cannot use the
 * AGP driver for some reason.
 */
static __init int init_k8_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;

	printk(KERN_INFO "PCI-DMA: Disabling AGP.\n");
	aper_size = aper_base = info->aper_size = 0;
	dev = NULL;
	for (i = 0; i < num_k8_northbridges; i++) {
		dev = k8_northbridges[i];
		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, 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");

	memset(gatt, 0, gatt_size);
	agp_gatt_table = gatt;

	for (i = 0; i < num_k8_northbridges; i++) {
		u32 gatt_reg;
		u32 ctl;

		dev = k8_northbridges[i];
		gatt_reg = __pa(gatt) >> 12;
		gatt_reg <<= 4;
		pci_write_config_dword(dev, 0x98, gatt_reg);
		pci_read_config_dword(dev, 0x90, &ctl);

		ctl |= 1;
		ctl &= ~((1<<4) | (1<<5));

		pci_write_config_dword(dev, 0x90, ctl);
	}
	flush_gart();

	printk(KERN_INFO "PCI-DMA: aperture base @ %x size %u KB\n",
	       aper_base, aper_size>>10);
	return 0;

 nommu:
	/* Should not happen anymore */
	printk(KERN_ERR "PCI-DMA: More than 4GB of RAM and no IOMMU\n"
	       KERN_ERR "PCI-DMA: 32bit PCI IO may malfunction.\n");
	return -1;
}

extern int agp_amd64_init(void);

static const struct dma_mapping_ops gart_dma_ops = {
	.mapping_error			= NULL,
	.map_single			= gart_map_single,
	.map_simple			= gart_map_simple,
	.unmap_single			= gart_unmap_single,
	.sync_single_for_cpu		= NULL,
	.sync_single_for_device		= NULL,
	.sync_single_range_for_cpu	= NULL,
	.sync_single_range_for_device	= NULL,
	.sync_sg_for_cpu		= NULL,
	.sync_sg_for_device		= NULL,
	.map_sg				= gart_map_sg,
	.unmap_sg			= gart_unmap_sg,
};

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

	if (no_agp && (dma_ops != &gart_dma_ops))
		return;

	for (i = 0; i < num_k8_northbridges; i++) {
		u32 ctl;

		dev = k8_northbridges[i];
		pci_read_config_dword(dev, 0x90, &ctl);

		ctl &= ~1;

		pci_write_config_dword(dev, 0x90, ctl);
	}
}

void __init gart_iommu_init(void)
{
	struct agp_kern_info info;
	unsigned long iommu_start;
	unsigned long aper_size;
	unsigned long scratch;
	long i;

	if (cache_k8_northbridges() < 0 || num_k8_northbridges == 0) {
		printk(KERN_INFO "PCI-GART: No AMD northbridge found.\n");
		return;
	}

#ifndef CONFIG_AGP_AMD64
	no_agp = 1;
#else
	/* Makefile puts PCI initialization via subsys_initcall first. */
	/* Add other K8 AGP bridge drivers here */
	no_agp = no_agp ||
		(agp_amd64_init() < 0) ||
		(agp_copy_info(agp_bridge, &info) < 0);
#endif

	if (swiotlb)
		return;

	/* Did we detect a different HW IOMMU? */
	if (iommu_detected && !gart_iommu_aperture)
		return;

	if (no_iommu ||
	    (!force_iommu && end_pfn <= MAX_DMA32_PFN) ||
	    !gart_iommu_aperture ||
	    (no_agp && init_k8_gatt(&info) < 0)) {
		if (end_pfn > MAX_DMA32_PFN) {
			printk(KERN_ERR "WARNING more than 4GB of memory "
					"but GART IOMMU not available.\n"
			       KERN_ERR "WARNING 32bit PCI may malfunction.\n");
		}
		return;
	}

	printk(KERN_INFO "PCI-DMA: using GART IOMMU.\n");
	aper_size = info.aper_size * 1024 * 1024;
	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,
						      get_order(iommu_pages/8));
	if (!iommu_gart_bitmap)
		panic("Cannot allocate iommu bitmap\n");
	memset(iommu_gart_bitmap, 0, iommu_pages/8);

#ifdef CONFIG_IOMMU_LEAK
	if (leak_trace) {
		iommu_leak_tab = (void *)__get_free_pages(GFP_KERNEL,
				  get_order(iommu_pages*sizeof(void *)));
		if (iommu_leak_tab)
			memset(iommu_leak_tab, 0, iommu_pages * 8);
		else
			printk(KERN_DEBUG
			       "PCI-DMA: Cannot allocate leak trace area\n");
	}
#endif

	/*
	 * Out of IOMMU space handling.
	 * Reserve some invalid pages at the beginning of the GART.
	 */
	set_bit_string(iommu_gart_bitmap, 0, EMERGENCY_PAGES);

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

	iommu_start = aper_size - iommu_size;
	iommu_bus_base = info.aper_base + iommu_start;
	bad_dma_address = iommu_bus_base;
	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);

	/*
	 * 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.
	 */
	scratch = get_zeroed_page(GFP_KERNEL);
	if (!scratch)
		panic("Cannot allocate iommu scratch page");
	gart_unmapped_entry = GPTE_ENCODE(__pa(scratch));
	for (i = EMERGENCY_PAGES; i < iommu_pages; i++)
		iommu_gatt_base[i] = gart_unmapped_entry;

	flush_gart();
	dma_ops = &gart_dma_ops;
}

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

#ifdef CONFIG_IOMMU_LEAK
	if (!strncmp(p, "leak", 4)) {
		leak_trace = 1;
		p += 4;
		if (*p == '=') ++p;
		if (isdigit(*p) && get_option(&p, &arg))
			iommu_leak_pages = arg;
	}
#endif
	if (isdigit(*p) && get_option(&p, &arg))
		iommu_size = arg;
	if (!strncmp(p, "fullflush", 8))
		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;
		}
	}
}