fit: Add device tree compression

This patch adds support for compressing individual device trees in the
FIT image. In order to make this efficient, we'll have to pull the
compatible property out of the FDT and store it directly in the config
node of the FIT image, so that we don't have to scan (and therefore
decompress) every single FDT on boot. Device tree compression is only
supported for FIT images that have this external compatible property.
For older images with no compression, we still support fallback to
scanning the FDT for the property.

This patch was adapted from depthcharge's http://crosreview.com/1553458

Change-Id: Ifcb6997782c480c8ef6692df17b66ad96264e623
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/32872
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/lib/fit_payload.c

@@ -96,6 +96,24 @@ static bool extract(struct region *region, struct fit_image_node *node)
 	return false;
 }
 
+static struct device_tree *unpack_fdt(struct fit_image_node *image_node)
+{
+	void *data = image_node->data;
+
+	if (image_node->compression != CBFS_COMPRESS_NONE) {
+		/* TODO: This is an ugly heuristic for how much the size will
+		   expand on decompression, fix once FIT images support storing
+		   the real uncompressed size. */
+		struct region r = { .offset = 0, .size = image_node->size * 5 };
+		data = malloc(r.size);
+		r.offset = (uintptr_t)data;
+		if (!data || extract(&r, image_node))
+			return NULL;
+	}
+
+	return fdt_unflatten(data);
+}
+
 /**
  * Add coreboot tables, CBMEM information and optional board specific strapping
  * IDs to the device tree loaded via FIT.
@@ -181,7 +199,7 @@ void fit_payload(struct prog *payload)
 		return;
 	}
 
-	dt = fdt_unflatten(config->fdt->data);
+	dt = unpack_fdt(config->fdt);
 	if (!dt) {
 		printk(BIOS_ERR, "ERROR: Failed to unflatten the FDT.\n");
 		rdev_munmap(prog_rdev(payload), data);