[PATCH v2 6/6] 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 spec update for DT overlay handoff[1], an overlay
must have the same top-level compatible string as its target base
DT has.
Before applying the DTO, it checks whether sufficient space is
reserved in the base FDT region. A margin (0x400) is used during
estimating the space size required by the merged DT.
A resizing happens if the reserved space is insufficient.
After all overlays are applied, it resizes to the actual size of the
merged DT.
Note that the margin (0x400) is arbitrary from experience, it might
not cover all possible scenarios as complex overlays with many
properties might require extra spaces and lead to FDT_ERR_NOSPACE
error.

[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.

 lib/fdtdec.c | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 81 insertions(+)

diff --git a/lib/fdtdec.c b/lib/fdtdec.c
index c38738b48c7..bd5e3c0aaea 100644
--- a/lib/fdtdec.c
+++ b/lib/fdtdec.c
@@ -1687,6 +1687,84 @@ 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_from_blob(void **blob, __maybe_unused int size)
+{
+	int ret;
+	struct fdt_header *live_fdt;
+	size_t new_fdt_size, actual_size;
+	int expand_by, blob_size;
+
+	if (!CONFIG_IS_ENABLED(OF_LIBFDT_OVERLAY) ||
+	    !CONFIG_IS_ENABLED(BLOBLIST))
+		return -EPERM;
+
+	ret = fdt_check_header(*blob);
+	if (ret)
+		return ret;
+
+	/* Get the total space reserved for FDT */
+	live_fdt = bloblist_get_blob(BLOBLISTT_CONTROL_FDT, &blob_size);
+	if (live_fdt != gd->fdt_blob)
+		return -ENOENT;
+
+	/* Make sure DTO has same top-level compatible string */
+	ret = fdtdec_match_dto_compatible(live_fdt, *blob);
+	if (ret)
+		return ret;
+
+	actual_size = fdt_totalsize(*blob);
+	/* Add margin for extra size growth after merging */
+	new_fdt_size = fdt_totalsize(live_fdt) + actual_size + 0x400;
+
+	/* Expand the FDT if the reserved size is not sufficient */
+	if (new_fdt_size > blob_size) {
+		ret = bloblist_resize(BLOBLISTT_CONTROL_FDT, new_fdt_size,
+				      &expand_by);
+		if (ret)
+			return ret;
+
+		/* The blob is shifted if it was following the FDT */
+		if (*blob > (void *)live_fdt)
+			*blob += expand_by;
+
+		ret = fdt_open_into(live_fdt, live_fdt, new_fdt_size);
+		if (ret)
+			return ret;
+	}
+
+	return fdt_overlay_apply_verbose(live_fdt, *blob);
+}
+
+static int fdtdec_apply_dto_done(void)
+{
+	int expand_by;
+	struct fdt_header *live_fdt = (struct fdt_header *)gd->fdt_blob;
+
+	fdt_pack(live_fdt);
+	return bloblist_resize(BLOBLISTT_CONTROL_FDT, fdt_totalsize(live_fdt),
+			       &expand_by);
+}
+
 int fdtdec_setup(void)
 {
 	int ret = -ENOENT;
@@ -1708,6 +1786,9 @@ int fdtdec_setup(void)
 				gd->fdt_src = FDTSRC_BLOBLIST;
 				log_debug("Devicetree is in bloblist at %p\n",
 					  gd->fdt_blob);
+				bloblist_apply_blobs(BLOBLISTT_FDT_OVERLAY,
+						     fdtdec_apply_dto_from_blob);
+				fdtdec_apply_dto_done();
 				goto setup_fdt;
 			} else {
 				log_debug("No FDT found in bloblist\n");
-- 
2.25.1