[PATCH] efi: efi-stub: notify on DTB absence

[msalter@redhat.com (Mark Salter)]

On Mon, 2014-10-20 at 19:29 +0100, Mark Rutland wrote:
> In the absence of an 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
> 
> Similarly, 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

Should we also include a positive acknowledgement of loader-provided
DTB? This could be UEFI itself or grub devicetree command or grub
generated minimal tree.

> 
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Acked-by: Leif Lindholm <leif.lindholm@linaro.org>
> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Cc: Mark Salter <msalter@redhat.com>
> Cc: Matt Fleming <matt.fleming@intel.com>
> Cc: Roy Franz <roy.franz@linaro.org>
> ---
>  drivers/firmware/efi/libstub/arm-stub.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/firmware/efi/libstub/arm-stub.c b/drivers/firmware/efi/libstub/arm-stub.c
> index 480339b..10abf24 100644
> --- a/drivers/firmware/efi/libstub/arm-stub.c
> +++ b/drivers/firmware/efi/libstub/arm-stub.c
> @@ -243,9 +243,16 @@ 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, "Generating empty DTB\n");
>  
>  	status = handle_cmdline_files(sys_table, image, cmdline_ptr,
>  				      "initrd=", dram_base + SZ_512M,