[PATCH v5 1/2] iommu/io-pgtable-arm: Add way to debug pgtable walk

[Rob Clark <robdclark@gmail.com>]

From: Rob Clark <robdclark@chromium.org>

Add an io-pgtable method to walk the pgtable returning the raw PTEs that
would be traversed for a given iova access.

Signed-off-by: Rob Clark <robdclark@chromium.org>
---
 drivers/iommu/io-pgtable-arm.c | 34 +++++++++++++++++++++++++---------
 include/linux/io-pgtable.h     | 16 ++++++++++++++++
 2 files changed, 41 insertions(+), 9 deletions(-)

diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
index 3d23b924cec1..24bbfd9a8874 100644
--- a/drivers/iommu/io-pgtable-arm.c
+++ b/drivers/iommu/io-pgtable-arm.c
@@ -690,8 +690,8 @@ static size_t arm_lpae_unmap_pages(struct io_pgtable_ops *ops, unsigned long iov
 				data->start_level, ptep);
 }
 
-static phys_addr_t arm_lpae_iova_to_phys(struct io_pgtable_ops *ops,
-					 unsigned long iova)
+static int arm_lpae_pgtable_walk(struct io_pgtable_ops *ops, unsigned long iova,
+				 struct io_pgtable_walk_data *wd)
 {
 	struct arm_lpae_io_pgtable *data = io_pgtable_ops_to_data(ops);
 	arm_lpae_iopte pte, *ptep = data->pgd;
@@ -700,7 +700,7 @@ static phys_addr_t arm_lpae_iova_to_phys(struct io_pgtable_ops *ops,
 	do {
 		/* Valid IOPTE pointer? */
 		if (!ptep)
-			return 0;
+			return -ENOENT;
 
 		/* Grab the IOPTE we're interested in */
 		ptep += ARM_LPAE_LVL_IDX(iova, lvl, data);
@@ -708,22 +708,37 @@ static phys_addr_t arm_lpae_iova_to_phys(struct io_pgtable_ops *ops,
 
 		/* Valid entry? */
 		if (!pte)
-			return 0;
+			return -ENOENT;
 
-		/* Leaf entry? */
+		wd->ptes[wd->level++] = pte;
+
+		/* Leaf entry?  If so, we've found the translation */
 		if (iopte_leaf(pte, lvl, data->iop.fmt))
-			goto found_translation;
+			return 0;
 
 		/* Take it to the next level */
 		ptep = iopte_deref(pte, data);
 	} while (++lvl < ARM_LPAE_MAX_LEVELS);
 
 	/* Ran out of page tables to walk */
-	return 0;
+	return -ENOENT;
+}
+
+static phys_addr_t arm_lpae_iova_to_phys(struct io_pgtable_ops *ops,
+					 unsigned long iova)
+{
+	struct arm_lpae_io_pgtable *data = io_pgtable_ops_to_data(ops);
+	struct io_pgtable_walk_data wd = {};
+	int ret, lvl;
+
+	ret = arm_lpae_pgtable_walk(ops, iova, &wd);
+	if (ret)
+		return 0;
+
+	lvl = wd.level + data->start_level;
 
-found_translation:
 	iova &= (ARM_LPAE_BLOCK_SIZE(lvl, data) - 1);
-	return iopte_to_paddr(pte, data) | iova;
+	return iopte_to_paddr(wd.ptes[wd.level - 1], data) | iova;
 }
 
 static void arm_lpae_restrict_pgsizes(struct io_pgtable_cfg *cfg)
@@ -804,6 +819,7 @@ arm_lpae_alloc_pgtable(struct io_pgtable_cfg *cfg)
 		.map_pages	= arm_lpae_map_pages,
 		.unmap_pages	= arm_lpae_unmap_pages,
 		.iova_to_phys	= arm_lpae_iova_to_phys,
+		.pgtable_walk	= arm_lpae_pgtable_walk,
 	};
 
 	return data;
diff --git a/include/linux/io-pgtable.h b/include/linux/io-pgtable.h
index 86cf1f7ae389..4d696724c7da 100644
--- a/include/linux/io-pgtable.h
+++ b/include/linux/io-pgtable.h
@@ -171,12 +171,26 @@ struct io_pgtable_cfg {
 	};
 };
 
+/**
+ * struct io_pgtable_walk_data - information from a pgtable walk
+ *
+ * @ptes:     The recorded PTE values from the walk
+ * @level:    The level of the last PTE
+ *
+ * @level also specifies the last valid index in @ptes
+ */
+struct io_pgtable_walk_data {
+	u64 ptes[4];
+	int level;
+};
+
 /**
  * struct io_pgtable_ops - Page table manipulation API for IOMMU drivers.
  *
  * @map_pages:    Map a physically contiguous range of pages of the same size.
  * @unmap_pages:  Unmap a range of virtually contiguous pages of the same size.
  * @iova_to_phys: Translate iova to physical address.
+ * @pgtable_walk: (optional) Perform a page table walk for a given iova.
  *
  * These functions map directly onto the iommu_ops member functions with
  * the same names.
@@ -190,6 +204,8 @@ struct io_pgtable_ops {
 			      struct iommu_iotlb_gather *gather);
 	phys_addr_t (*iova_to_phys)(struct io_pgtable_ops *ops,
 				    unsigned long iova);
+	int (*pgtable_walk)(struct io_pgtable_ops *ops, unsigned long iova,
+			    struct io_pgtable_walk_data *wd);
 	int (*read_and_clear_dirty)(struct io_pgtable_ops *ops,
 				    unsigned long iova, size_t size,
 				    unsigned long flags,
-- 
2.45.2