Re: [PATCH v2 06/15] ARM: i.MX: scratch: add FDT support

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

On 2/4/26 9:01 PM, 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 | 24 ++++++++++++++++++++++++
>  common/Kconfig              | 14 ++++++++++++++
>  include/mach/imx/scratch.h  |  2 ++
>  3 files changed, 40 insertions(+)
> 
> diff --git a/arch/arm/mach-imx/scratch.c b/arch/arm/mach-imx/scratch.c
> index e4e2d25969f061c9fcdfd7c3d87701b715eb2805..da138445dfb352f2f3497be77004aefc7d46f188 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 +95,24 @@ const struct optee_header *imx_scratch_get_optee_hdr(void)
>  
>  	return &scratch->optee_hdr;
>  }
> +
> +u8 *imx_scratch_get_fdt(unsigned int *fdt_sz)
> +{
> +	unsigned int sz;
> +
> +	if (!scratch) {
> +		if (IN_PBL)
> +			return ERR_PTR(-EINVAL);
> +		else
> +			scratch = (void *)arm_mem_scratch_get();
> +	}
> +
> +	sz = sizeof(scratch->fdt);
> +	if (sz == 0)
> +		return NULL;
> +
> +	if (fdt_sz)
> +		*fdt_sz = sz;
> +
> +	return scratch->fdt;
> +}
> diff --git a/common/Kconfig b/common/Kconfig
> index 50c26695b2b56a943edfd00a7e0cb1067ad269a9..265652900a5632177d36efa84d590be6db2e7015 100644
> --- a/common/Kconfig
> +++ b/common/Kconfig
> @@ -304,6 +304,20 @@ config SCRATCH_SIZE
>  	default 0x8000
>  	prompt "Scratch size"
>  
> +config SCRATCH_FDT_SIZE
> +	hex
> +	default 0x0
> +	prompt "Scratch FDT size"
> +	help
> +	  The size of the scratch area used as destination to load and optional
> +	  decompress the barebox builtin DTB into it. Can be 0x0 if early FDT
> +	  support is not requied.
> +
> +	  If specified, SCRATCH_FDT_SIZE <= SCRATCH_SIZE must be ensured.
> +
> +	  This option should match the OP-TEE's CFG_DTB_MAX_SIZE configuration
> +	  if used by OP-TEE.

AFAIU, this is a workaround because OP-TEE doesn't accept outside
information about how big the DTB buffer is, just its base address.

In that case, this should go to security/Kconfig and be named something
like PBL_OPTEE_DTB_MAX_SIZE. There's no need to ask every user that
configures barebox about this.


Cheers,
Ahmad

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