Booting via bootm offers several methods to load oftree data. When no
dedicated oftree image is provided, barebox checks for the presence of
its own internal oftree, assuming it as a good choice for boot.

This fallback method breaks the usecase when a modern OF-based barebox
is used to boot a legacy ATAG dependent non OF based vendor provided kernel
(e.g. ATAGs will be switched off).
Unfortunately those kernels are being still actively shipped today.

Change barebox according to the principle of least surprise: when no
oftree data is proactively configured, then perform a non-oftree boot.
Make the fallback-use of the barebox internal oftree an opt-in feature.

Note: this will break boards where the boot process relied on this feature,
e.g.: oftree based barebox plus oftree based kernel without an explicit
given dts. For those boards global.bootm.internal_oftree_fallback=1 should
be set.

Signed-off-by: Alexander Kurz <ak...@blala.de>
---
 common/bootm.c  | 8 ++++++--
 include/bootm.h | 2 ++
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/common/bootm.c b/common/bootm.c
index 5984319..f5303fa 100644
--- a/common/bootm.c
+++ b/common/bootm.c
@@ -58,6 +58,7 @@ void bootm_data_init_defaults(struct bootm_data *data)
        data->initrd_address = UIMAGE_INVALID_ADDRESS;
        data->os_address = UIMAGE_SOME_ADDRESS;
        data->oftree_file = getenv_nonempty("global.bootm.oftree");
+       data->internal_oftree_fallback = 
getenv_nonempty("global.bootm.internal_oftree_fallback");
        data->os_file = getenv_nonempty("global.bootm.image");
        getenv_ul("global.bootm.image.loadaddr", &data->os_address);
        getenv_ul("global.bootm.initrd.loadaddr", &data->initrd_address);
@@ -375,14 +376,15 @@ int bootm_load_devicetree(struct image_data *data, 
unsigned long load_address)
                        pr_err("unable to unflatten devicetree\n");
                        return -EINVAL;
                }
-
-       } else {
+       } else if (data->internal_oftree_fallback) {
                data->of_root_node = of_get_root_node();
                if (!data->of_root_node)
                        return 0;
 
                if (bootm_verbose(data) > 1 && data->of_root_node)
                        printf("using internal devicetree\n");
+       } else {
+               return 0;
        }
 
        if (data->initrd_res) {
@@ -530,6 +532,7 @@ int bootm_boot(struct bootm_data *bootm_data)
        data->verify = bootm_data->verify;
        data->force = bootm_data->force;
        data->dryrun = bootm_data->dryrun;
+       data->internal_oftree_fallback = bootm_data->internal_oftree_fallback;
        data->initrd_address = bootm_data->initrd_address;
        data->os_address = bootm_data->os_address;
        data->os_entry = bootm_data->os_entry;
@@ -683,6 +686,7 @@ BAREBOX_MAGICVAR_NAMED(global_bootm_image_loadaddr, 
global.bootm.image.loadaddr,
 BAREBOX_MAGICVAR_NAMED(global_bootm_initrd, global.bootm.initrd, "bootm 
default initrd");
 BAREBOX_MAGICVAR_NAMED(global_bootm_initrd_loadaddr, 
global.bootm.initrd.loadaddr, "bootm default initrd loadaddr");
 BAREBOX_MAGICVAR_NAMED(global_bootm_oftree, global.bootm.oftree, "bootm 
default oftree");
+BAREBOX_MAGICVAR_NAMED(global_bootm_internal_oftree_fallback, 
global.bootm.internal_oftree_fallback, "use barebox oftree as fallback");
 BAREBOX_MAGICVAR_NAMED(global_bootm_verify, global.bootm.verify, "bootm 
default verify level");
 BAREBOX_MAGICVAR_NAMED(global_bootm_verbose, global.bootm.verify, "bootm 
default verbosity level (0=quiet)");
 BAREBOX_MAGICVAR_NAMED(global_bootm_appendroot, global.bootm.appendroot, "Add 
root= option to Kernel to mount rootfs from the device the Kernel comes from");
diff --git a/include/bootm.h b/include/bootm.h
index 6e9777a..c945c99 100644
--- a/include/bootm.h
+++ b/include/bootm.h
@@ -20,6 +20,7 @@ struct bootm_data {
        enum bootm_verify verify;
        bool force;
        bool dryrun;
+       bool internal_oftree_fallback;
        /*
         * appendroot - if true, try to add a suitable root= Kernel option to
         * mount the rootfs from the same device as the Kernel comes from.
@@ -81,6 +82,7 @@ struct image_data {
        int verbose;
        int force;
        int dryrun;
+       int internal_oftree_fallback;
 };
 
 struct image_handler {
-- 
2.1.4


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