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Date:	Thu, 23 Oct 2014 16:33:33 +0100
From:	Mark Rutland <>
	Mark Rutland <>
Subject: [PATCHv2] efi: efi-stub: notify on DTB absence

Since v1 [1]:
* Add a positive acknowledgement for a configuration table DTB
* Fixed a couple of typos in the commit message

Ard, Leif, Roy, I've assumed your acks from v1 are still valid with the
additional print. Please shout if that's not the case.



In the absence of a DTB configuration table, the EFI stub will happily
continue attempting to boot a kernel, despite the fact that this kernel
may not function without a description of the hardware. In this case, as
with a typo'd "dtb=" option (e.g. "dbt=") or many other possible
failures, the only output seen by the user will be the rather terse
output from the EFI stub:

EFI stub: Booting Linux Kernel...

To aid those attempting to debug such failures, this patch adds a notice
when no DTB is found, making the output more helpful:

EFI stub: Booting Linux Kernel...
EFI stub: Generating empty DTB

Additionally, a positive acknowledgement is added when a user-specified
DTB is in use:

EFI stub: Booting Linux Kernel...
EFI stub: Using DTB from command line

Similarly, a positive acknowledgement is added when a DTB from a
configuration table is in use:

EFI stub: Booting Linux Kernel...
EFI stub: Using DTB from configuration table

Signed-off-by: Mark Rutland <>
Acked-by: Leif Lindholm <>
Acked-by: Ard Biesheuvel <>
Cc: Mark Salter <>
Cc: Matt Fleming <>
Acked-by: Roy Franz <>
 drivers/firmware/efi/libstub/arm-stub.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/libstub/arm-stub.c b/drivers/firmware/efi/libstub/arm-stub.c
index 480339b..21fa50e 100644
--- a/drivers/firmware/efi/libstub/arm-stub.c
+++ b/drivers/firmware/efi/libstub/arm-stub.c
@@ -243,9 +243,18 @@ unsigned long __init efi_entry(void *handle, efi_system_table_t *sys_table,
 			goto fail_free_cmdline;
-	if (!fdt_addr)
+	if (fdt_addr) {
+		pr_efi(sys_table, "Using DTB from command line\n");
+	} else {
 		/* Look for a device tree configuration table entry. */
 		fdt_addr = (uintptr_t)get_fdt(sys_table);
+		if (fdt_addr)
+			pr_efi(sys_table, "Using DTB from configuration table\n");
+	}
+	if (!fdt_addr)
+		pr_efi(sys_table, "Generating empty DTB\n");
 	status = handle_cmdline_files(sys_table, image, cmdline_ptr,
 				      "initrd=", dram_base + SZ_512M,

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