1 files changed, 160 insertions, 0 deletions
diff --git a/drivers/gpu/drm/xe/xe_pt_walk.c b/drivers/gpu/drm/xe/xe_pt_walk.c
new file mode 100644
index 000000000000..8f6c8d063f39
--- /dev/null
+++ b/drivers/gpu/drm/xe/xe_pt_walk.c
@@ -0,0 +1,160 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright © 2022 Intel Corporation
+ */
+#include "xe_pt_walk.h"
+
+/**
+ * DOC: GPU page-table tree walking.
+ * The utilities in this file are similar to the CPU page-table walk
+ * utilities in mm/pagewalk.c. The main difference is that we distinguish
+ * the various levels of a page-table tree with an unsigned integer rather
+ * than by name. 0 is the lowest level, and page-tables with level 0 can
+ * not be directories pointing to lower levels, whereas all other levels
+ * can. The user of the utilities determines the highest level.
+ *
+ * Nomenclature:
+ * Each struct xe_ptw, regardless of level is referred to as a page table, and
+ * multiple page tables typically form a page table tree with page tables at
+ * intermediate levels being page directories pointing at page tables at lower
+ * levels. A shared page table for a given address range is a page-table which
+ * is neither fully within nor fully outside the address range and that can
+ * thus be shared by two or more address ranges.
+ *
+ * Please keep this code generic so that it can used as a drm-wide page-
+ * table walker should other drivers find use for it.
+ */
+static u64 xe_pt_addr_end(u64 addr, u64 end, unsigned int level,
+			  const struct xe_pt_walk *walk)
+{
+	u64 size = 1ull << walk->shifts[level];
+	u64 tmp = round_up(addr + 1, size);
+
+	return min_t(u64, tmp, end);
+}
+
+static bool xe_pt_next(pgoff_t *offset, u64 *addr, u64 next, u64 end,
+		       unsigned int level, const struct xe_pt_walk *walk)
+{
+	pgoff_t step = 1;
+
+	/* Shared pt walk skips to the last pagetable */
+	if (unlikely(walk->shared_pt_mode)) {
+		unsigned int shift = walk->shifts[level];
+		u64 skip_to = round_down(end, 1ull << shift);
+
+		if (skip_to > next) {
+			step += (skip_to - next) >> shift;
+			next = skip_to;
+		}
+	}
+
+	*addr = next;
+	*offset += step;
+
+	return next != end;
+}
+
+/**
+ * xe_pt_walk_range() - Walk a range of a gpu page table tree with callbacks
+ * for each page-table entry in all levels.
+ * @parent: The root page table for walk start.
+ * @level: The root page table level.
+ * @addr: Virtual address start.
+ * @end: Virtual address end + 1.
+ * @walk: Walk info.
+ *
+ * Similar to the CPU page-table walker, this is a helper to walk
+ * a gpu page table and call a provided callback function for each entry.
+ *
+ * Return: 0 on success, negative error code on error. The error is
+ * propagated from the callback and on error the walk is terminated.
+ */
+int xe_pt_walk_range(struct xe_ptw *parent, unsigned int level,
+		     u64 addr, u64 end, struct xe_pt_walk *walk)
+{
+	pgoff_t offset = xe_pt_offset(addr, level, walk);
+	struct xe_ptw **entries = parent->dir ? parent->dir->entries : NULL;
+	const struct xe_pt_walk_ops *ops = walk->ops;
+	enum page_walk_action action;
+	struct xe_ptw *child;
+	int err = 0;
+	u64 next;
+
+	do {
+		next = xe_pt_addr_end(addr, end, level, walk);
+		if (walk->shared_pt_mode && xe_pt_covers(addr, next, level,
+							 walk))
+			continue;
+again:
+		action = ACTION_SUBTREE;
+		child = entries ? entries[offset] : NULL;
+		err = ops->pt_entry(parent, offset, level, addr, next,
+				    &child, &action, walk);
+		if (err)
+			break;
+
+		/* Probably not needed yet for gpu pagetable walk. */
+		if (unlikely(action == ACTION_AGAIN))
+			goto again;
+
+		if (likely(!level || !child || action == ACTION_CONTINUE))
+			continue;
+
+		err = xe_pt_walk_range(child, level - 1, addr, next, walk);
+
+		if (!err && ops->pt_post_descend)
+			err = ops->pt_post_descend(parent, offset, level, addr,
+						   next, &child, &action, walk);
+		if (err)
+			break;
+
+	} while (xe_pt_next(&offset, &addr, next, end, level, walk));
+
+	return err;
+}
+
+/**
+ * xe_pt_walk_shared() - Walk shared page tables of a page-table tree.
+ * @parent: Root page table directory.
+ * @level: Level of the root.
+ * @addr: Start address.
+ * @end: Last address + 1.
+ * @walk: Walk info.
+ *
+ * This function is similar to xe_pt_walk_range() but it skips page tables
+ * that are private to the range. Since the root (or @parent) page table is
+ * typically also a shared page table this function is different in that it
+ * calls the pt_entry callback and the post_descend callback also for the
+ * root. The root can be detected in the callbacks by checking whether
+ * parent == *child.
+ * Walking only the shared page tables is common for unbind-type operations
+ * where the page-table entries for an address range are cleared or detached
+ * from the main page-table tree.
+ *
+ * Return: 0 on success, negative error code on error: If a callback
+ * returns an error, the walk will be terminated and the error returned by
+ * this function.
+ */
+int xe_pt_walk_shared(struct xe_ptw *parent, unsigned int level,
+		      u64 addr, u64 end, struct xe_pt_walk *walk)
+{
+	const struct xe_pt_walk_ops *ops = walk->ops;
+	enum page_walk_action action = ACTION_SUBTREE;
+	struct xe_ptw *child = parent;
+	int err;
+
+	walk->shared_pt_mode = true;
+	err = walk->ops->pt_entry(parent, 0, level + 1, addr, end,
+				  &child, &action, walk);
+
+	if (err || action != ACTION_SUBTREE)
+		return err;
+
+	err = xe_pt_walk_range(parent, level, addr, end, walk);
+	if (!err && ops->pt_post_descend) {
+		err = ops->pt_post_descend(parent, 0, level + 1, addr, end,
+					   &child, &action, walk);
+	}
+	return err;
+}