regions: add mmap helper device

In order to facilitate platforms which need a buffer cache
for performing boot device operations provide infrastructure
to share the logic in managing the buffer and operations.

Change-Id: I45dd9f213029706ff92a3e5a2c9edd5e8b541e27
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/9132
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/lib/region.c

@@ -161,3 +161,41 @@ const struct region_device_ops mem_rdev_ops = {
 	.munmap = mdev_munmap,
 	.readat = mdev_readat,
 };
+
+void mmap_helper_device_init(struct mmap_helper_region_device *mdev,
+				void *cache, size_t cache_size)
+{
+	mem_pool_init(&mdev->pool, cache, cache_size);
+}
+
+void *mmap_helper_rdev_mmap(const struct region_device *rd, size_t offset,
+				size_t size)
+{
+	struct mmap_helper_region_device *mdev;
+	void *mapping;
+
+	mdev = container_of((void *)rd, typeof(*mdev), rdev);
+
+	mapping = mem_pool_alloc(&mdev->pool, size);
+
+	if (mapping == NULL)
+		return NULL;
+
+	if (rd->ops->readat(rd, mapping, offset, size) != size) {
+		mem_pool_free(&mdev->pool, mapping);
+		return NULL;
+	}
+
+	return mapping;
+}
+
+int mmap_helper_rdev_munmap(const struct region_device *rd, void *mapping)
+{
+	struct mmap_helper_region_device *mdev;
+
+	mdev = container_of((void *)rd, typeof(*mdev), rdev);
+
+	mem_pool_free(&mdev->pool, mapping);
+
+	return 0;
+}