[U-Boot] [RFC PATCH] arm: bootm: Boot kernel with U-Boot's FDT blob

[Michal Simek]

On 11.1.2017 06:19, Lokesh Vutla wrote:
> 
> 
> On Tuesday 10 January 2017 06:28 PM, Michal Simek wrote:
>> U-Boot configured via DTB can use the same DTB for booting the kernel.
>> When OF_CONTROL is used fdtcontroladdr is setup and can be use for boot.
>>
>> Signed-off-by: Michal Simek <michal.simek at xilinx.com>
>> ---
>>
>> Didn't check if there is any side effect or not but it looks weird when
>> you have DT driver u-boot that you have to load dtb again.
>>
>> ---
>>  arch/arm/lib/bootm.c | 14 ++++++++++++++
>>  1 file changed, 14 insertions(+)
>>
>> diff --git a/arch/arm/lib/bootm.c b/arch/arm/lib/bootm.c
>> index 43cc83ec95b6..9740045b0094 100644
>> --- a/arch/arm/lib/bootm.c
>> +++ b/arch/arm/lib/bootm.c
>> @@ -245,6 +245,20 @@ static void boot_prep_linux(bootm_headers_t *images)
>>  		}
>>  		setup_board_tags(&params);
>>  		setup_end_tag(gd->bd);
>> +	} else if (IS_ENABLED(CONFIG_OF_CONTROL)) {
>> +#ifdef CONFIG_OF_LIBFDT
>> +		images->ft_addr = (char *)getenv_hex("fdtcontroladdr", 0);
> 
> If your intent is to use U-Boot's fdt as fallback, why can't we just use
> gd->fdt_blob instead of getting from env?

Not an issue to use gd->fdt_block instead but I expect we should copy it
to the different location too.

> 
> IMO, this is not the right place to get the fallback fdt. Instead it
> should fallback at bootm_get_fdt() so that other parameters like
> images->ft_length is also updated. Can you try the following diff?

Not a problem to move it to this position.

I have tried it and system is not booting.

> 
> diff --git a/common/image-fdt.c b/common/image-fdt.c
> index e7540be8d6..f8714b3702 100644
> --- a/common/image-fdt.c
> +++ b/common/image-fdt.c
> @@ -238,7 +238,6 @@ int boot_get_fdt(int flag, int argc, char * const
> argv[], uint8_t arch,
>  	int		fdt_noffset;
>  #endif
>  	const char *select = NULL;
> -	int		ok_no_fdt = 0;
> 
>  	*of_flat_tree = NULL;
>  	*of_size = 0;
> @@ -311,7 +310,7 @@ int boot_get_fdt(int flag, int argc, char * const
> argv[], uint8_t arch,
>  			       fdt_addr);
>  			fdt_hdr = image_get_fdt(fdt_addr);
>  			if (!fdt_hdr)
> -				goto no_fdt;
> +				goto fallback_fdt;
> 
>  			/*
>  			 * move image data to the load address,
> @@ -381,7 +380,7 @@ int boot_get_fdt(int flag, int argc, char * const
> argv[], uint8_t arch,
>  			break;
>  		default:
>  			puts("ERROR: Did not find a cmdline Flattened Device Tree\n");


This probably requires some code around not to show this error message
because it should be valid boot option.

> -			goto no_fdt;
> +			goto fallback_fdt;
>  		}
> 
>  		printf("   Booting using the fdt blob at %#08lx\n", fdt_addr);
> @@ -415,11 +414,17 @@ int boot_get_fdt(int flag, int argc, char * const
> argv[], uint8_t arch,
>  			}
>  		} else {
>  			debug("## No Flattened Device Tree\n");
> -			goto no_fdt;
> +			goto fallback_fdt;
>  		}
>  	} else {
>  		debug("## No Flattened Device Tree\n");
> -		goto no_fdt;
> +		goto fallback_fdt;
> +	}
> +
> +fallback_fdt:
> +	if (!fdt_blob) {
> +		printf("## Using U-boot's fdt to boot kernel\n");
> +		fdt_blob = (char *)gd->fdt_blob;
>  	}
> 
>  	*of_flat_tree = fdt_blob;
> @@ -429,12 +434,10 @@ int boot_get_fdt(int flag, int argc, char * const
> argv[], uint8_t arch,
> 
>  	return 0;
> 
> -no_fdt:
> -	ok_no_fdt = 1;
>  error:
>  	*of_flat_tree = NULL;
>  	*of_size = 0;
> -	if (!select && ok_no_fdt) {
> +	if (!select) {
>  		debug("Continuing to boot without FDT\n");
>  		return 0;
>  	}
> 
> Thanks and regards,
> Lokesh
> 

Thanks,
Michal