Re: [PATCH 10/23] ARM: i.MX: scratch: add FDT support

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

Hi,

On 11/11/25 3:14 PM, Sascha Hauer wrote:
> On Mon, Nov 10, 2025 at 09:34:50PM +0100, Marco Felsch wrote:
>> Add support to store a FDT within the scratch area. The user needs to
>> query the location and size via imx_scratch_get_fdt() which can be used
>> afterwards to write the actual FDT into it.
>>
>> Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
>> ---
>>  arch/arm/mach-imx/scratch.c | 16 ++++++++++++++++
>>  common/Kconfig              | 14 ++++++++++++++
>>  include/mach/imx/scratch.h  |  2 ++
>>  3 files changed, 32 insertions(+)
>>
>> diff --git a/arch/arm/mach-imx/scratch.c b/arch/arm/mach-imx/scratch.c
>> index e4e2d25969f061c9fcdfd7c3d87701b715eb2805..9c0f1c09c4e0b863d8c95888db7cf0518f698d53 100644
>> --- a/arch/arm/mach-imx/scratch.c
>> +++ b/arch/arm/mach-imx/scratch.c
>> @@ -16,7 +16,10 @@ struct imx_scratch_space {
>>  	u32 bootrom_log[128];
>>  	u32 reserved[128];		/* reserve for bootrom log */
>>  	struct optee_header optee_hdr;
>> +	/* FDT needs an 8 byte alignment */
>> +	u8 fdt[CONFIG_SCRATCH_FDT_SIZE] __aligned(8);
>>  };
>> +static_assert(sizeof(struct imx_scratch_space) <= CONFIG_SCRATCH_SIZE);
>>  
>>  static struct imx_scratch_space *scratch;
>>  
>> @@ -92,3 +95,16 @@ const struct optee_header *imx_scratch_get_optee_hdr(void)
>>  
>>  	return &scratch->optee_hdr;
>>  }
>> +
>> +void imx_scratch_get_fdt(void **fdt, unsigned int *fdt_sz)
>> +{
>> +	if (!scratch) {
>> +		if (IN_PBL)
>> +			return;
>> +		else
>> +			scratch = (void *)arm_mem_scratch_get();
>> +	}
>> +
>> +	*fdt = scratch->fdt;
>> +	*fdt_sz = sizeof(scratch->fdt);
>> +}
>> diff --git a/common/Kconfig b/common/Kconfig
>> index eb2fb1da1e0919b6e7d5e868c48ad2e195cd8aa8..3f394416c3c376d1cf842472803a47462bb012ed 100644
>> --- a/common/Kconfig
>> +++ b/common/Kconfig
>> @@ -302,8 +302,22 @@ config MALLOC_SIZE
>>  config SCRATCH_SIZE
>>  	hex
>>  	default 0x8000
>> +	default 0x48000 if PBL_EARLY_FDT_LOAD

Easy to misconfigure. How about an additional:

range 0x48000 <some big size> if PBL_EARLY_FDT_LOAD

>>  	prompt "Scratch size"
> 
> Do I get this right that the scratch space now includes the space for
> the early FDT? If yes then this can lead to inconsistencies when the
> scratch space is to small. Why not add an extra space?

I would prefer we do not complicate the "endmem" layout more than we
have currently.

What I think we want in future is an API to allocate from the scratch
mem a handoff block and there would be no hardcoded offsets and struct
imx_scratch_space could go away. To save handoff when switching from PBL
to proper, we would then also allocate to the scratch space.

This will probably happen separately, so I am in favor of not creating a
new section that's removed afterwards.

Cheers,
Ahmad

> 
> Sascha
> 

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