efi: efi-stub: notify on DTB absence

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 <mark.rutland@arm.com>
Acked-by: Leif Lindholm <leif.lindholm@linaro.org>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Roy Franz <roy.franz@linaro.org>
Acked-by: Matt Fleming <matt.fleming@intel.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

1 files changed, 10 insertions, 1 deletions

diff --git a/drivers/firmware/efi/libstub/arm-stub.c b/drivers/firmware/efi/libstub/arm-stub.c
index 75ee05964cbc..eb48a1a1a576 100644
--- a/drivers/firmware/efi/libstub/arm-stub.c
+++ b/drivers/firmware/efi/libstub/arm-stub.c
@@ -247,9 +247,18 @@ 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,