[PATCH v3 5/6] fdtdec: apply DT overlays from bloblist

[Raymond Mao]

During FDT setup, apply all existing DT overlays from the bloblist
to the base FDT if bloblist is being used for handoff from previous
boot stage.
According to the Firmware Handoff spec update to support DT overlay [1],
an overlay must have the same top-level compatible string as its target
base DT has.
Before applying the overlays, check whether sufficient space is
reserved in the base DT blob, if not, resize the blob to the allowed
padded size, which is limited by CONFIG_SYS_FDT_PAD and the bloblist
spare space size.
After all overlays are applied, resize the merged DT to its actual size.

[1] Add Transfer Entry for Devicetree Overlay
https://github.com/FirmwareHandoff/firmware_handoff/pull/74

Signed-off-by: Raymond Mao <raymond.mao at linaro.org>
---
Changes in v2:
- Add more details into the commit message.
- Check and compare the top-level compatible string of DT/DTO.
- Check the reserved space in the base DT region, and skip resizing if
  the space is sufficient.
- Move the DT space shrinking to the end after all DT overlays are
  applied.
Changes in v3:
- Move resizing to the beginning and only do one time.
- The max size to resize depends on SYS_FDT_PAD and the spare space left
  in the bloblist.
- Renaming and misc refactoring.

 lib/fdtdec.c | 80 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 80 insertions(+)

diff --git a/lib/fdtdec.c b/lib/fdtdec.c
index c38738b48c7..630b7d2bd69 100644
--- a/lib/fdtdec.c
+++ b/lib/fdtdec.c
@@ -1687,6 +1687,83 @@ void fdtdec_setup_embed(void)
 	gd->fdt_src = FDTSRC_EMBED;
 }
 
+static int fdtdec_match_dto_compatible(const void *base, const void *dto)
+{
+	const char *compat_base;
+	const char *compat_dto;
+	int len;
+
+	compat_base = (const char *)fdt_getprop(base, 0, "compatible", &len);
+	if (!compat_base || len <= 0)
+		return -ENOENT;
+
+	compat_dto = (const char *)fdt_getprop(dto, 0, "compatible", &len);
+	if (!compat_dto || len <= 0)
+		return -ENOENT;
+
+	if (strcmp(compat_base, compat_dto))
+		return -EPERM;
+
+	return 0;
+}
+
+static int fdtdec_apply_dto_blob(void **blob, __maybe_unused int size)
+{
+	int ret;
+
+	ret = fdt_check_header(*blob);
+	if (ret)
+		return ret;
+
+	ret = fdtdec_match_dto_compatible(gd->fdt_blob, *blob);
+	if (ret)
+		return ret;
+
+	return fdt_overlay_apply_verbose((void *)gd->fdt_blob, *blob);
+}
+
+static int fdtdec_apply_bloblist_dtos(void)
+{
+	int ret;
+	struct fdt_header *live_fdt;
+	int blob_size;
+	size_t padded_size, max_size;
+
+	if (!CONFIG_IS_ENABLED(OF_LIBFDT_OVERLAY) ||
+	    !CONFIG_IS_ENABLED(BLOBLIST))
+		return 0;
+
+	/* Get the total space reserved for FDT in blob */
+	live_fdt = bloblist_get_blob(BLOBLISTT_CONTROL_FDT, &blob_size);
+	if (live_fdt != gd->fdt_blob)
+		return -ENOENT;
+
+	/* Calculate the allowed padded size */
+	padded_size = fdt_totalsize(live_fdt) + CONFIG_SYS_FDT_PAD;
+	max_size = bloblist_get_total_size() - bloblist_get_size() + blob_size;
+	if (padded_size > max_size)
+		padded_size = max_size;
+
+	/* Resize if the current space is not sufficient */
+	if (blob_size < padded_size) {
+		ret = bloblist_resize(BLOBLISTT_CONTROL_FDT, padded_size);
+		if (ret)
+			return ret;
+
+		ret = fdt_open_into(live_fdt, live_fdt, padded_size);
+		if (ret)
+			return ret;
+	}
+
+	ret = bloblist_apply_blobs(BLOBLISTT_FDT_OVERLAY, fdtdec_apply_dto_blob);
+	if (ret)
+		return ret;
+
+	/* Shink the blob to the actual FDT size */
+	fdt_pack(live_fdt);
+	return bloblist_resize(BLOBLISTT_CONTROL_FDT, fdt_totalsize(live_fdt));
+}
+
 int fdtdec_setup(void)
 {
 	int ret = -ENOENT;
@@ -1708,6 +1785,9 @@ int fdtdec_setup(void)
 				gd->fdt_src = FDTSRC_BLOBLIST;
 				log_debug("Devicetree is in bloblist at %p\n",
 					  gd->fdt_blob);
+				ret = fdtdec_apply_bloblist_dtos();
+				if (ret)
+					return ret;
 				goto setup_fdt;
 			} else {
 				log_debug("No FDT found in bloblist\n");
-- 
2.25.1