Patrick Georgi submitted this change.

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memrange: Add support for stealing required memory from given ranges

This change adds memranges_steal() which allows the user
to steal memory from the list of available ranges by providing a set
of constraints (limit, size, alignment, tag). It tries to find the
first big enough range that can satisfy the constraints, creates a
hole as per the request and returns base of the stolen memory.

BUG=b:149186922

Signed-off-by: Furquan Shaikh <furquan@google.com>
Change-Id: Ibe9cfae18fc6101ab2e7e27233e45324c8117708
Reviewed-on: https://review.coreboot.org/c/coreboot/+/39484
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
---
M src/include/memrange.h
M src/lib/memrange.c
2 files changed, 70 insertions(+), 0 deletions(-)

diff --git a/src/include/memrange.h b/src/include/memrange.h
index 0d20236..f8fa033 100644
--- a/src/include/memrange.h
+++ b/src/include/memrange.h
@@ -16,6 +16,7 @@
 #define MEMRANGE_H_
 
 #include <device/resource.h>
+#include <stdbool.h>
 
 /* A memranges structure consists of a list of range_entry(s). The structure
  * is exposed so that a memranges can be used on the stack if needed. */
@@ -166,4 +167,18 @@
 /* Returns next entry after the provided entry. NULL if r is last. */
 struct range_entry *memranges_next_entry(struct memranges *ranges,
 					 const struct range_entry *r);
+
+/* Steals memory from the available list in given ranges as per the constraints:
+ * limit = Upper bound for the memory range to steal.
+ * size  = Requested size for the stolen memory.
+ * align = Alignment requirements for the starting address of the stolen memory.
+ *         (Alignment must be a power of 2).
+ * tag   = Use a range that matches the given tag.
+ *
+ * If the constraints can be satisfied, this function creates a hole in the memrange,
+ * writes the base address of that hole to stolen_base and returns true. Otherwise it returns
+ * false. */
+bool memranges_steal(struct memranges *ranges, resource_t limit, resource_t size, size_t align,
+		     unsigned long tag, resource_t *stolen_base);
+
 #endif /* MEMRANGE_H_ */
diff --git a/src/lib/memrange.c b/src/lib/memrange.c
index 21fff00..b9c09e8 100644
--- a/src/lib/memrange.c
+++ b/src/lib/memrange.c
@@ -391,3 +391,58 @@
 {
 	return r->next;
 }
+
+/* Find a range entry that satisfies the given constraints to fit a hole that matches the
+ * required alignment, is big enough, does not exceed the limit and has a matching tag. */
+static const struct range_entry *memranges_find_entry(struct memranges *ranges,
+						      resource_t limit, resource_t size,
+						      size_t align, unsigned long tag)
+{
+	const struct range_entry *r;
+	resource_t base, end;
+
+	if (size == 0)
+		return NULL;
+
+	if (!IS_POWER_OF_2(align))
+		return NULL;
+
+	if (!IS_ALIGNED(align, ranges->align))
+		return NULL;
+
+	memranges_each_entry(r, ranges) {
+
+		if (r->tag != tag)
+			continue;
+
+		base = ALIGN_UP(r->begin, align);
+		end = base + size - 1;
+
+		if (end > r->end)
+			continue;
+
+		if (end > limit)
+			continue;
+
+		return r;
+	}
+
+	return NULL;
+}
+
+bool memranges_steal(struct memranges *ranges, resource_t limit, resource_t size, size_t align,
+		     unsigned long tag, resource_t *stolen_base)
+{
+	resource_t base;
+	const struct range_entry *r = memranges_find_entry(ranges, limit, size, align, tag);
+
+	if (r == NULL)
+		return false;
+
+	base = ALIGN_UP(r->begin, align);
+
+	memranges_create_hole(ranges, base, size);
+	*stolen_base = base;
+
+	return true;
+}

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