[ptxdist] [PATCH 2/5] kernel-fit: Allow using 'kernel_noload' as sub-image type

[Alexander Dahl <ada@thorsis.com>]

Multi platform kernels built by the kernel-fit rule before are not
usable in U-Boot, which adheres more strictly to the Flat Image Tree
(FIT) spec than barebox does.  For image sub-type 'kernel' U-Boot
expects valid 'load' and 'entry' addresses.  Setting those addresses to
a generic value is impossible however for generic kernels, e.g. the
DistroKit v7a kernel needs different addresses on at91 SAMA5 than
on i.MX6.  barebox circumvents this by ignoring missing 'load' and
'entry' addresses and finding a suitable address by itself.  For using
generic kernels in U-Boot you need sub-image type 'kernel_noload' and
dummy addresses, which is also supported in barebox from v2024.01.0
release onwards.

Link: https://github.com/open-source-firmware/flat-image-tree/releases/download/v0.8/fit-specification-v0.8.pdf
Link: https://lore.barebox.org/barebox/20231129203106.2417486-1-a.fatoum@pengutronix.de/
Signed-off-by: Alexander Dahl <ada@thorsis.com>
---
 platforms/kernel-fit.in            | 17 +++++++++++++++++
 scripts/lib/ptxd_make_fit_image.sh | 20 +++++++++++++++-----
 2 files changed, 32 insertions(+), 5 deletions(-)

diff --git a/platforms/kernel-fit.in b/platforms/kernel-fit.in
index 0e82889b9..5b160c57d 100644
--- a/platforms/kernel-fit.in
+++ b/platforms/kernel-fit.in
@@ -17,14 +17,31 @@ menuconfig KERNEL_FIT
 
 if KERNEL_FIT
 
+config KERNEL_FIT_NOLOAD
+	bool
+	prompt "Sub-image type 'kernel_noload'"
+	help
+	  Use 'kernel_noload' as sub-image type for the kernel, setting
+	  the load address and entry address to dummy values as required
+	  by the FIT image specification.
+	  Useful for booting kernels supporting multiple boards with
+	  U-Boot, e.g. the platform-v7a kernel of DistroKit.
+	  U-Boot supports this since release v2011.12.
+
+	  Note: barebox added support with release v2024.01.0.
+	  You can leave this option disabled if you only use barebox.
+	  You should not enable this if you use older barebox versions.
+
 config KERNEL_FIT_LOAD
 	string
+	depends on !KERNEL_FIT_NOLOAD
 	prompt "Kernel load address (optional)"
 	help
 	  Required by most bootloaders. Optional for Barebox.
 
 config KERNEL_FIT_ENTRY
 	string
+	depends on !KERNEL_FIT_NOLOAD
 	prompt "Kernel entry address (optional)"
 	help
 	  Required by most bootloaders. Optional for Barebox.
diff --git a/scripts/lib/ptxd_make_fit_image.sh b/scripts/lib/ptxd_make_fit_image.sh
index dd0f63b7b..4b99e6fbf 100644
--- a/scripts/lib/ptxd_make_fit_image.sh
+++ b/scripts/lib/ptxd_make_fit_image.sh
@@ -19,20 +19,30 @@ ptxd_make_image_fit_its() {
 		kernel {
 			description = "kernel";
 			data = /incbin/("${image_kernel}");
-			type = "kernel";
 			arch = "$(ptxd_get_ptxconf PTXCONF_ARCH_STRING)";
 			os = "linux";
 			compression = "none";
 EOF
-    if [ -n "$(ptxd_get_ptxconf PTXCONF_KERNEL_FIT_LOAD)" ]; then
+    if [ -n "$(ptxd_get_ptxconf PTXCONF_KERNEL_FIT_NOLOAD)" ]; then
         cat << EOF
+			type = "kernel_noload";
+			load = <0x00000000>;
+			entry = <0x00000000>;
+EOF
+    else
+        cat << EOF
+			type = "kernel";
+EOF
+        if [ -n "$(ptxd_get_ptxconf PTXCONF_KERNEL_FIT_LOAD)" ]; then
+            cat << EOF
 			load = <$(ptxd_get_ptxconf PTXCONF_KERNEL_FIT_LOAD)>;
 EOF
-    fi
-    if [ -n "$(ptxd_get_ptxconf PTXCONF_KERNEL_FIT_ENTRY)" ]; then
-        cat << EOF
+        fi
+        if [ -n "$(ptxd_get_ptxconf PTXCONF_KERNEL_FIT_ENTRY)" ]; then
+            cat << EOF
 			entry = <$(ptxd_get_ptxconf PTXCONF_KERNEL_FIT_ENTRY)>;
 EOF
+        fi
     fi
     cat << EOF
 			hash-1 {
-- 
2.39.2