1 files changed, 180 insertions, 293 deletions

diff --git a/drivers/iommu/tegra-gart.c b/drivers/iommu/tegra-gart.c
index da6a4e357b2b..4d8057916552 100644
--- a/drivers/iommu/tegra-gart.c
+++ b/drivers/iommu/tegra-gart.c
@@ -1,5 +1,5 @@
 /*
- * IOMMU API for GART in Tegra20
+ * IOMMU API for Graphics Address Relocation Table on Tegra20
  *
  * Copyright (c) 2010-2012, NVIDIA CORPORATION.  All rights reserved.
  *
@@ -19,101 +19,75 @@
  * 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#define pr_fmt(fmt)	"%s(): " fmt, __func__
+#define dev_fmt(fmt)	"gart: " fmt
 
-#include <linux/init.h>
+#include <linux/io.h>
+#include <linux/iommu.h>
 #include <linux/moduleparam.h>
 #include <linux/platform_device.h>
-#include <linux/spinlock.h>
 #include <linux/slab.h>
+#include <linux/spinlock.h>
 #include <linux/vmalloc.h>
-#include <linux/mm.h>
-#include <linux/list.h>
-#include <linux/device.h>
-#include <linux/io.h>
-#include <linux/iommu.h>
-#include <linux/of.h>
-
-#include <asm/cacheflush.h>
 
-/* bitmap of the page sizes currently supported */
-#define GART_IOMMU_PGSIZES	(SZ_4K)
+#include <soc/tegra/mc.h>
 
 #define GART_REG_BASE		0x24
 #define GART_CONFIG		(0x24 - GART_REG_BASE)
 #define GART_ENTRY_ADDR		(0x28 - GART_REG_BASE)
 #define GART_ENTRY_DATA		(0x2c - GART_REG_BASE)
-#define GART_ENTRY_PHYS_ADDR_VALID	(1 << 31)
+
+#define GART_ENTRY_PHYS_ADDR_VALID	BIT(31)
 
 #define GART_PAGE_SHIFT		12
 #define GART_PAGE_SIZE		(1 << GART_PAGE_SHIFT)
-#define GART_PAGE_MASK						\
-	(~(GART_PAGE_SIZE - 1) & ~GART_ENTRY_PHYS_ADDR_VALID)
+#define GART_PAGE_MASK		GENMASK(30, GART_PAGE_SHIFT)
 
-struct gart_client {
-	struct device		*dev;
-	struct list_head	list;
-};
+/* bitmap of the page sizes currently supported */
+#define GART_IOMMU_PGSIZES	(GART_PAGE_SIZE)
 
 struct gart_device {
 	void __iomem		*regs;
 	u32			*savedata;
-	u32			page_count;	/* total remappable size */
-	dma_addr_t		iovmm_base;	/* offset to vmm_area */
+	unsigned long		iovmm_base;	/* offset to vmm_area start */
+	unsigned long		iovmm_end;	/* offset to vmm_area end */
 	spinlock_t		pte_lock;	/* for pagetable */
-	struct list_head	client;
-	spinlock_t		client_lock;	/* for client list */
-	struct device		*dev;
-
+	spinlock_t		dom_lock;	/* for active domain */
+	unsigned int		active_devices;	/* number of active devices */
+	struct iommu_domain	*active_domain;	/* current active domain */
 	struct iommu_device	iommu;		/* IOMMU Core handle */
-};
-
-struct gart_domain {
-	struct iommu_domain domain;		/* generic domain handle */
-	struct gart_device *gart;		/* link to gart device   */
+	struct device		*dev;
 };
 
 static struct gart_device *gart_handle; /* unique for a system */
 
 static bool gart_debug;
 
-#define GART_PTE(_pfn)						\
-	(GART_ENTRY_PHYS_ADDR_VALID | ((_pfn) << PAGE_SHIFT))
-
-static struct gart_domain *to_gart_domain(struct iommu_domain *dom)
-{
-	return container_of(dom, struct gart_domain, domain);
-}
-
 /*
  * Any interaction between any block on PPSB and a block on APB or AHB
  * must have these read-back to ensure the APB/AHB bus transaction is
  * complete before initiating activity on the PPSB block.
  */
-#define FLUSH_GART_REGS(gart)	((void)readl((gart)->regs + GART_CONFIG))
+#define FLUSH_GART_REGS(gart)	readl_relaxed((gart)->regs + GART_CONFIG)
 
 #define for_each_gart_pte(gart, iova)					\
 	for (iova = gart->iovmm_base;					\
-	     iova < gart->iovmm_base + GART_PAGE_SIZE * gart->page_count; \
+	     iova < gart->iovmm_end;					\
 	     iova += GART_PAGE_SIZE)
 
 static inline void gart_set_pte(struct gart_device *gart,
-				unsigned long offs, u32 pte)
+				unsigned long iova, unsigned long pte)
 {
-	writel(offs, gart->regs + GART_ENTRY_ADDR);
-	writel(pte, gart->regs + GART_ENTRY_DATA);
-
-	dev_dbg(gart->dev, "%s %08lx:%08x\n",
-		 pte ? "map" : "unmap", offs, pte & GART_PAGE_MASK);
+	writel_relaxed(iova, gart->regs + GART_ENTRY_ADDR);
+	writel_relaxed(pte, gart->regs + GART_ENTRY_DATA);
 }
 
 static inline unsigned long gart_read_pte(struct gart_device *gart,
-					  unsigned long offs)
+					  unsigned long iova)
 {
 	unsigned long pte;
 
-	writel(offs, gart->regs + GART_ENTRY_ADDR);
-	pte = readl(gart->regs + GART_ENTRY_DATA);
+	writel_relaxed(iova, gart->regs + GART_ENTRY_ADDR);
+	pte = readl_relaxed(gart->regs + GART_ENTRY_DATA);
 
 	return pte;
 }
@@ -125,224 +99,155 @@ static void do_gart_setup(struct gart_device *gart, const u32 *data)
 	for_each_gart_pte(gart, iova)
 		gart_set_pte(gart, iova, data ? *(data++) : 0);
 
-	writel(1, gart->regs + GART_CONFIG);
+	writel_relaxed(1, gart->regs + GART_CONFIG);
 	FLUSH_GART_REGS(gart);
 }
 
-#ifdef DEBUG
-static void gart_dump_table(struct gart_device *gart)
-{
-	unsigned long iova;
-	unsigned long flags;
-
-	spin_lock_irqsave(&gart->pte_lock, flags);
-	for_each_gart_pte(gart, iova) {
-		unsigned long pte;
-
-		pte = gart_read_pte(gart, iova);
-
-		dev_dbg(gart->dev, "%s %08lx:%08lx\n",
-			(GART_ENTRY_PHYS_ADDR_VALID & pte) ? "v" : " ",
-			iova, pte & GART_PAGE_MASK);
-	}
-	spin_unlock_irqrestore(&gart->pte_lock, flags);
-}
-#else
-static inline void gart_dump_table(struct gart_device *gart)
+static inline bool gart_iova_range_invalid(struct gart_device *gart,
+					   unsigned long iova, size_t bytes)
 {
+	return unlikely(iova < gart->iovmm_base || bytes != GART_PAGE_SIZE ||
+			iova + bytes > gart->iovmm_end);
 }
-#endif
 
-static inline bool gart_iova_range_valid(struct gart_device *gart,
-					 unsigned long iova, size_t bytes)
+static inline bool gart_pte_valid(struct gart_device *gart, unsigned long iova)
 {
-	unsigned long iova_start, iova_end, gart_start, gart_end;
-
-	iova_start = iova;
-	iova_end = iova_start + bytes - 1;
-	gart_start = gart->iovmm_base;
-	gart_end = gart_start + gart->page_count * GART_PAGE_SIZE - 1;
-
-	if (iova_start < gart_start)
-		return false;
-	if (iova_end > gart_end)
-		return false;
-	return true;
+	return !!(gart_read_pte(gart, iova) & GART_ENTRY_PHYS_ADDR_VALID);
 }
 
 static int gart_iommu_attach_dev(struct iommu_domain *domain,
 				 struct device *dev)
 {
-	struct gart_domain *gart_domain = to_gart_domain(domain);
-	struct gart_device *gart = gart_domain->gart;
-	struct gart_client *client, *c;
-	int err = 0;
-
-	client = devm_kzalloc(gart->dev, sizeof(*c), GFP_KERNEL);
-	if (!client)
-		return -ENOMEM;
-	client->dev = dev;
-
-	spin_lock(&gart->client_lock);
-	list_for_each_entry(c, &gart->client, list) {
-		if (c->dev == dev) {
-			dev_err(gart->dev,
-				"%s is already attached\n", dev_name(dev));
-			err = -EINVAL;
-			goto fail;
-		}
+	struct gart_device *gart = gart_handle;
+	int ret = 0;
+
+	spin_lock(&gart->dom_lock);
+
+	if (gart->active_domain && gart->active_domain != domain) {
+		ret = -EBUSY;
+	} else if (dev->archdata.iommu != domain) {
+		dev->archdata.iommu = domain;
+		gart->active_domain = domain;
+		gart->active_devices++;
 	}
-	list_add(&client->list, &gart->client);
-	spin_unlock(&gart->client_lock);
-	dev_dbg(gart->dev, "Attached %s\n", dev_name(dev));
-	return 0;
 
-fail:
-	devm_kfree(gart->dev, client);
-	spin_unlock(&gart->client_lock);
-	return err;
+	spin_unlock(&gart->dom_lock);
+
+	return ret;
 }
 
 static void gart_iommu_detach_dev(struct iommu_domain *domain,
 				  struct device *dev)
 {
-	struct gart_domain *gart_domain = to_gart_domain(domain);
-	struct gart_device *gart = gart_domain->gart;
-	struct gart_client *c;
-
-	spin_lock(&gart->client_lock);
-
-	list_for_each_entry(c, &gart->client, list) {
-		if (c->dev == dev) {
-			list_del(&c->list);
-			devm_kfree(gart->dev, c);
-			dev_dbg(gart->dev, "Detached %s\n", dev_name(dev));
-			goto out;
-		}
+	struct gart_device *gart = gart_handle;
+
+	spin_lock(&gart->dom_lock);
+
+	if (dev->archdata.iommu == domain) {
+		dev->archdata.iommu = NULL;
+
+		if (--gart->active_devices == 0)
+			gart->active_domain = NULL;
 	}
-	dev_err(gart->dev, "Couldn't find\n");
-out:
-	spin_unlock(&gart->client_lock);
+
+	spin_unlock(&gart->dom_lock);
 }
 
 static struct iommu_domain *gart_iommu_domain_alloc(unsigned type)
 {
-	struct gart_domain *gart_domain;
-	struct gart_device *gart;
+	struct iommu_domain *domain;
 
 	if (type != IOMMU_DOMAIN_UNMANAGED)
 		return NULL;
 
-	gart = gart_handle;
-	if (!gart)
-		return NULL;
-
-	gart_domain = kzalloc(sizeof(*gart_domain), GFP_KERNEL);
-	if (!gart_domain)
-		return NULL;
-
-	gart_domain->gart = gart;
-	gart_domain->domain.geometry.aperture_start = gart->iovmm_base;
-	gart_domain->domain.geometry.aperture_end = gart->iovmm_base +
-					gart->page_count * GART_PAGE_SIZE - 1;
-	gart_domain->domain.geometry.force_aperture = true;
+	domain = kzalloc(sizeof(*domain), GFP_KERNEL);
+	if (domain) {
+		domain->geometry.aperture_start = gart_handle->iovmm_base;
+		domain->geometry.aperture_end = gart_handle->iovmm_end - 1;
+		domain->geometry.force_aperture = true;
+	}
 
-	return &gart_domain->domain;
+	return domain;
 }
 
 static void gart_iommu_domain_free(struct iommu_domain *domain)
 {
-	struct gart_domain *gart_domain = to_gart_domain(domain);
-	struct gart_device *gart = gart_domain->gart;
-
-	if (gart) {
-		spin_lock(&gart->client_lock);
-		if (!list_empty(&gart->client)) {
-			struct gart_client *c;
-
-			list_for_each_entry(c, &gart->client, list)
-				gart_iommu_detach_dev(domain, c->dev);
-		}
-		spin_unlock(&gart->client_lock);
+	WARN_ON(gart_handle->active_domain == domain);
+	kfree(domain);
+}
+
+static inline int __gart_iommu_map(struct gart_device *gart, unsigned long iova,
+				   unsigned long pa)
+{
+	if (unlikely(gart_debug && gart_pte_valid(gart, iova))) {
+		dev_err(gart->dev, "Page entry is in-use\n");
+		return -EINVAL;
 	}
 
-	kfree(gart_domain);
+	gart_set_pte(gart, iova, GART_ENTRY_PHYS_ADDR_VALID | pa);
+
+	return 0;
 }
 
 static int gart_iommu_map(struct iommu_domain *domain, unsigned long iova,
 			  phys_addr_t pa, size_t bytes, int prot)
 {
-	struct gart_domain *gart_domain = to_gart_domain(domain);
-	struct gart_device *gart = gart_domain->gart;
-	unsigned long flags;
-	unsigned long pfn;
-	unsigned long pte;
+	struct gart_device *gart = gart_handle;
+	int ret;
 
-	if (!gart_iova_range_valid(gart, iova, bytes))
+	if (gart_iova_range_invalid(gart, iova, bytes))
 		return -EINVAL;
 
-	spin_lock_irqsave(&gart->pte_lock, flags);
-	pfn = __phys_to_pfn(pa);
-	if (!pfn_valid(pfn)) {
-		dev_err(gart->dev, "Invalid page: %pa\n", &pa);
-		spin_unlock_irqrestore(&gart->pte_lock, flags);
+	spin_lock(&gart->pte_lock);
+	ret = __gart_iommu_map(gart, iova, (unsigned long)pa);
+	spin_unlock(&gart->pte_lock);
+
+	return ret;
+}
+
+static inline int __gart_iommu_unmap(struct gart_device *gart,
+				     unsigned long iova)
+{
+	if (unlikely(gart_debug && !gart_pte_valid(gart, iova))) {
+		dev_err(gart->dev, "Page entry is invalid\n");
 		return -EINVAL;
 	}
-	if (gart_debug) {
-		pte = gart_read_pte(gart, iova);
-		if (pte & GART_ENTRY_PHYS_ADDR_VALID) {
-			spin_unlock_irqrestore(&gart->pte_lock, flags);
-			dev_err(gart->dev, "Page entry is in-use\n");
-			return -EBUSY;
-		}
-	}
-	gart_set_pte(gart, iova, GART_PTE(pfn));
-	FLUSH_GART_REGS(gart);
-	spin_unlock_irqrestore(&gart->pte_lock, flags);
+
+	gart_set_pte(gart, iova, 0);
+
 	return 0;
 }
 
 static size_t gart_iommu_unmap(struct iommu_domain *domain, unsigned long iova,
 			       size_t bytes)
 {
-	struct gart_domain *gart_domain = to_gart_domain(domain);
-	struct gart_device *gart = gart_domain->gart;
-	unsigned long flags;
+	struct gart_device *gart = gart_handle;
+	int err;
 
-	if (!gart_iova_range_valid(gart, iova, bytes))
+	if (gart_iova_range_invalid(gart, iova, bytes))
 		return 0;
 
-	spin_lock_irqsave(&gart->pte_lock, flags);
-	gart_set_pte(gart, iova, 0);
-	FLUSH_GART_REGS(gart);
-	spin_unlock_irqrestore(&gart->pte_lock, flags);
-	return bytes;
+	spin_lock(&gart->pte_lock);
+	err = __gart_iommu_unmap(gart, iova);
+	spin_unlock(&gart->pte_lock);
+
+	return err ? 0 : bytes;
 }
 
 static phys_addr_t gart_iommu_iova_to_phys(struct iommu_domain *domain,
 					   dma_addr_t iova)
 {
-	struct gart_domain *gart_domain = to_gart_domain(domain);
-	struct gart_device *gart = gart_domain->gart;
+	struct gart_device *gart = gart_handle;
 	unsigned long pte;
-	phys_addr_t pa;
-	unsigned long flags;
 
-	if (!gart_iova_range_valid(gart, iova, 0))
+	if (gart_iova_range_invalid(gart, iova, GART_PAGE_SIZE))
 		return -EINVAL;
 
-	spin_lock_irqsave(&gart->pte_lock, flags);
+	spin_lock(&gart->pte_lock);
 	pte = gart_read_pte(gart, iova);
-	spin_unlock_irqrestore(&gart->pte_lock, flags);
+	spin_unlock(&gart->pte_lock);
 
-	pa = (pte & GART_PAGE_MASK);
-	if (!pfn_valid(__phys_to_pfn(pa))) {
-		dev_err(gart->dev, "No entry for %08llx:%pa\n",
-			 (unsigned long long)iova, &pa);
-		gart_dump_table(gart);
-		return -EINVAL;
-	}
-	return pa;
+	return pte & GART_PAGE_MASK;
 }
 
 static bool gart_iommu_capable(enum iommu_cap cap)
@@ -352,8 +257,12 @@ static bool gart_iommu_capable(enum iommu_cap cap)
 
 static int gart_iommu_add_device(struct device *dev)
 {
-	struct iommu_group *group = iommu_group_get_for_dev(dev);
+	struct iommu_group *group;
+
+	if (!dev->iommu_fwspec)
+		return -ENODEV;
 
+	group = iommu_group_get_for_dev(dev);
 	if (IS_ERR(group))
 		return PTR_ERR(group);
 
@@ -370,6 +279,17 @@ static void gart_iommu_remove_device(struct device *dev)
 	iommu_device_unlink(&gart_handle->iommu, dev);
 }
 
+static int gart_iommu_of_xlate(struct device *dev,
+			       struct of_phandle_args *args)
+{
+	return 0;
+}
+
+static void gart_iommu_sync(struct iommu_domain *domain)
+{
+	FLUSH_GART_REGS(gart_handle);
+}
+
 static const struct iommu_ops gart_iommu_ops = {
 	.capable	= gart_iommu_capable,
 	.domain_alloc	= gart_iommu_domain_alloc,
@@ -383,129 +303,96 @@ static const struct iommu_ops gart_iommu_ops = {
 	.unmap		= gart_iommu_unmap,
 	.iova_to_phys	= gart_iommu_iova_to_phys,
 	.pgsize_bitmap	= GART_IOMMU_PGSIZES,
+	.of_xlate	= gart_iommu_of_xlate,
+	.iotlb_sync_map	= gart_iommu_sync,
+	.iotlb_sync	= gart_iommu_sync,
 };
 
-static int tegra_gart_suspend(struct device *dev)
+int tegra_gart_suspend(struct gart_device *gart)
 {
-	struct gart_device *gart = dev_get_drvdata(dev);
-	unsigned long iova;
 	u32 *data = gart->savedata;
-	unsigned long flags;
+	unsigned long iova;
+
+	/*
+	 * All GART users shall be suspended at this point. Disable
+	 * address translation to trap all GART accesses as invalid
+	 * memory accesses.
+	 */
+	writel_relaxed(0, gart->regs + GART_CONFIG);
+	FLUSH_GART_REGS(gart);
 
-	spin_lock_irqsave(&gart->pte_lock, flags);
 	for_each_gart_pte(gart, iova)
 		*(data++) = gart_read_pte(gart, iova);
-	spin_unlock_irqrestore(&gart->pte_lock, flags);
+
 	return 0;
 }
 
-static int tegra_gart_resume(struct device *dev)
+int tegra_gart_resume(struct gart_device *gart)
 {
-	struct gart_device *gart = dev_get_drvdata(dev);
-	unsigned long flags;
-
-	spin_lock_irqsave(&gart->pte_lock, flags);
 	do_gart_setup(gart, gart->savedata);
-	spin_unlock_irqrestore(&gart->pte_lock, flags);
+
 	return 0;
 }
 
-static int tegra_gart_probe(struct platform_device *pdev)
+struct gart_device *tegra_gart_probe(struct device *dev, struct tegra_mc *mc)
 {
 	struct gart_device *gart;
-	struct resource *res, *res_remap;
-	void __iomem *gart_regs;
-	struct device *dev = &pdev->dev;
-	int ret;
-
-	if (gart_handle)
-		return -EIO;
+	struct resource *res;
+	int err;
 
 	BUILD_BUG_ON(PAGE_SHIFT != GART_PAGE_SHIFT);
 
 	/* the GART memory aperture is required */
-	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
-	res_remap = platform_get_resource(pdev, IORESOURCE_MEM, 1);
-	if (!res || !res_remap) {
-		dev_err(dev, "GART memory aperture expected\n");
-		return -ENXIO;
-	}
-
-	gart = devm_kzalloc(dev, sizeof(*gart), GFP_KERNEL);
-	if (!gart) {
-		dev_err(dev, "failed to allocate gart_device\n");
-		return -ENOMEM;
+	res = platform_get_resource(to_platform_device(dev), IORESOURCE_MEM, 1);
+	if (!res) {
+		dev_err(dev, "Memory aperture resource unavailable\n");
+		return ERR_PTR(-ENXIO);
 	}
 
-	gart_regs = devm_ioremap(dev, res->start, resource_size(res));
-	if (!gart_regs) {
-		dev_err(dev, "failed to remap GART registers\n");
-		return -ENXIO;
-	}
-
-	ret = iommu_device_sysfs_add(&gart->iommu, &pdev->dev, NULL,
-				     dev_name(&pdev->dev));
-	if (ret) {
-		dev_err(dev, "Failed to register IOMMU in sysfs\n");
-		return ret;
-	}
-
-	iommu_device_set_ops(&gart->iommu, &gart_iommu_ops);
+	gart = kzalloc(sizeof(*gart), GFP_KERNEL);
+	if (!gart)
+		return ERR_PTR(-ENOMEM);
 
-	ret = iommu_device_register(&gart->iommu);
-	if (ret) {
-		dev_err(dev, "Failed to register IOMMU\n");
-		iommu_device_sysfs_remove(&gart->iommu);
-		return ret;
-	}
+	gart_handle = gart;
 
-	gart->dev = &pdev->dev;
+	gart->dev = dev;
+	gart->regs = mc->regs + GART_REG_BASE;
+	gart->iovmm_base = res->start;
+	gart->iovmm_end = res->end + 1;
 	spin_lock_init(&gart->pte_lock);
-	spin_lock_init(&gart->client_lock);
-	INIT_LIST_HEAD(&gart->client);
-	gart->regs = gart_regs;
-	gart->iovmm_base = (dma_addr_t)res_remap->start;
-	gart->page_count = (resource_size(res_remap) >> GART_PAGE_SHIFT);
-
-	gart->savedata = vmalloc(array_size(sizeof(u32), gart->page_count));
-	if (!gart->savedata) {
-		dev_err(dev, "failed to allocate context save area\n");
-		return -ENOMEM;
-	}
+	spin_lock_init(&gart->dom_lock);
 
-	platform_set_drvdata(pdev, gart);
 	do_gart_setup(gart, NULL);
 
-	gart_handle = gart;
+	err = iommu_device_sysfs_add(&gart->iommu, dev, NULL, "gart");
+	if (err)
+		goto free_gart;
 
-	return 0;
-}
+	iommu_device_set_ops(&gart->iommu, &gart_iommu_ops);
+	iommu_device_set_fwnode(&gart->iommu, dev->fwnode);
 
-static const struct dev_pm_ops tegra_gart_pm_ops = {
-	.suspend	= tegra_gart_suspend,
-	.resume		= tegra_gart_resume,
-};
+	err = iommu_device_register(&gart->iommu);
+	if (err)
+		goto remove_sysfs;
 
-static const struct of_device_id tegra_gart_of_match[] = {
-	{ .compatible = "nvidia,tegra20-gart", },
-	{ },
-};
+	gart->savedata = vmalloc(resource_size(res) / GART_PAGE_SIZE *
+				 sizeof(u32));
+	if (!gart->savedata) {
+		err = -ENOMEM;
+		goto unregister_iommu;
+	}
 
-static struct platform_driver tegra_gart_driver = {
-	.probe		= tegra_gart_probe,
-	.driver = {
-		.name	= "tegra-gart",
-		.pm	= &tegra_gart_pm_ops,
-		.of_match_table = tegra_gart_of_match,
-		.suppress_bind_attrs = true,
-	},
-};
+	return gart;
 
-static int __init tegra_gart_init(void)
-{
-	return platform_driver_register(&tegra_gart_driver);
+unregister_iommu:
+	iommu_device_unregister(&gart->iommu);
+remove_sysfs:
+	iommu_device_sysfs_remove(&gart->iommu);
+free_gart:
+	kfree(gart);
+
+	return ERR_PTR(err);
 }
-subsys_initcall(tegra_gart_init);
 
 module_param(gart_debug, bool, 0644);
 MODULE_PARM_DESC(gart_debug, "Enable GART debugging");