kernel-fitimage: skip FDT section creation for applicable symlinks

When building a FIT image with device trees, each device tree lands in a
FIT section and is referenced by a FIT configuration node.

FIT images however also allow referencing the same device tree from
multiple configurations. This can be useful to reduce FIT image size
while staying compatible with existing bootloaders. Allow
kernel-fitimage.bbclass users to take advantage of this by mapping
each symlink to a regular device tree included in the FIT to a
configuration that references a common device tree section.

(From OE-Core rev: 21e240da63239826f3ef50ceef40c9519e9030d8)

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 32 insertions, 1 deletions

diff --git a/meta/classes-recipe/kernel-fitimage.bbclass b/meta/classes-recipe/kernel-fitimage.bbclass
index 6307e3c50a..7980910aa8 100644
--- a/meta/classes-recipe/kernel-fitimage.bbclass
+++ b/meta/classes-recipe/kernel-fitimage.bbclass
@@ -355,6 +355,27 @@ EOF
 }
 
 #
+# echoes symlink destination if it points below directory
+#
+# $1 ... file that's a potential symlink
+# $2 ... expected parent directory
+symlink_points_below() {
+        file="$2/$1"
+        dir=$2
+
+        if ! [ -L "$file" ]; then
+                return
+        fi
+
+        realpath="$(realpath --relative-to=$dir $file)"
+        if [ -z "${realpath%%../*}" ]; then
+                return
+        fi
+
+        echo "$realpath"
+}
+
+#
 # Emit the fitImage ITS configuration section
 #
 # $1 ... .its filename
@@ -392,7 +413,13 @@ fitimage_emit_section_config() {
         setup_line=""
         default_line=""
 
+        dtb_image_sect=$(symlink_points_below $dtb_image "${EXTERNAL_KERNEL_DEVICETREE}")
+        if [ -z "$dtb_image_sect" ]; then
+                dtb_image_sect=$dtb_image
+        fi
+
         dtb_image=$(echo $dtb_image | tr '/' '_')
+        dtb_image_sect=$(echo "${dtb_image_sect}" | tr '/' '_')
 
         # conf node name is selected based on dtb ID if it is present,
         # otherwise its selected based on kernel ID
@@ -411,7 +438,7 @@ fitimage_emit_section_config() {
         if [ -n "$dtb_image" ]; then
                 conf_desc="$conf_desc${sep}FDT blob"
                 sep=", "
-                fdt_line="fdt = \"fdt-$dtb_image\";"
+                fdt_line="fdt = \"fdt-$dtb_image_sect\";"
         fi
 
         if [ -n "$ramdisk_id" ]; then
@@ -568,6 +595,10 @@ fitimage_assemble() {
                         echo "$DTBS" | tr ' ' '\n' | grep -xq "$DTB" && continue
 
                         DTBS="$DTBS $DTB"
+
+                        # Also skip if a symlink. We'll later have each config section point at it
+                        [ $(symlink_points_below $DTB "${EXTERNAL_KERNEL_DEVICETREE}") ] && continue
+
                         DTB=$(echo $DTB | tr '/' '_')
                         fitimage_emit_section_dtb $1 $DTB "${EXTERNAL_KERNEL_DEVICETREE}/$DTB"
                 done