iommu/io-pgtable-arm: Add way to debug pgtable walk

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>
Reviewed-by: Mostafa Saleh <smostafa@google.com>
Link: https://lore.kernel.org/r/20241210165127.600817-4-robdclark@gmail.com
[will: Removed 'arm_lpae_io_pgtable_walk_data::level' per Mostafa]
Signed-off-by: Will Deacon <will@kernel.org>

Author: robclark

drivers/iommu/io-pgtable-arm.c

@@ -754,6 +754,28 @@ static phys_addr_t arm_lpae_iova_to_phys(struct io_pgtable_ops *ops,
 	return iopte_to_paddr(d.pte, data) | iova;
 }
 
+static int visit_pgtable_walk(struct io_pgtable_walk_data *walk_data, int lvl,
+			      arm_lpae_iopte *ptep, size_t size)
+{
+	struct arm_lpae_io_pgtable_walk_data *data = walk_data->data;
+	data->ptes[lvl] = *ptep;
+	return 0;
+}
+
+static int arm_lpae_pgtable_walk(struct io_pgtable_ops *ops, unsigned long iova,
+				 void *wd)
+{
+	struct arm_lpae_io_pgtable *data = io_pgtable_ops_to_data(ops);
+	struct io_pgtable_walk_data walk_data = {
+		.data = wd,
+		.visit = visit_pgtable_walk,
+		.addr = iova,
+		.end = iova + 1,
+	};
+
+	return __arm_lpae_iopte_walk(data, &walk_data, data->pgd, data->start_level);
+}
+
 static int io_pgtable_visit(struct arm_lpae_io_pgtable *data,
 			    struct io_pgtable_walk_data *walk_data,
 			    arm_lpae_iopte *ptep, int lvl)
@@ -929,6 +951,7 @@ arm_lpae_alloc_pgtable(struct io_pgtable_cfg *cfg)
 		.unmap_pages	= arm_lpae_unmap_pages,
 		.iova_to_phys	= arm_lpae_iova_to_phys,
 		.read_and_clear_dirty = arm_lpae_read_and_clear_dirty,
+		.pgtable_walk	= arm_lpae_pgtable_walk,
 	};
 
 	return data;

include/linux/io-pgtable.h

@@ -180,12 +180,22 @@ struct io_pgtable_cfg {
 	};
 };
 
+/**
+ * struct arm_lpae_io_pgtable_walk_data - information from a pgtable walk
+ *
+ * @ptes:     The recorded PTE values from the walk
+ */
+struct arm_lpae_io_pgtable_walk_data {
+	u64 ptes[4];
+};
+
 /**
  * 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.
@@ -199,6 +209,7 @@ 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, void *wd);
 	int (*read_and_clear_dirty)(struct io_pgtable_ops *ops,
 				    unsigned long iova, size_t size,
 				    unsigned long flags,