Re: [PATCH 20/23] ARM: i.MX8M: Add support to extract OP-TEE provided informations

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

Hi,

On 11/17/25 10:15 AM, Sascha Hauer wrote:
> On Mon, Nov 10, 2025 at 09:35:00PM +0100, Marco Felsch wrote:
>> Extract the OP-TEE overlay fragements information into a dedicated
>> overlay buffer and add the handoff data on success. The handoff data is
>> used by next commit.
>>
>> Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
>> ---
>>  arch/arm/mach-imx/esdctl.c | 40 ++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 40 insertions(+)
>>
>> diff --git a/arch/arm/mach-imx/esdctl.c b/arch/arm/mach-imx/esdctl.c
>> index 964d438e3f3433332e351d9a70f91857ee33e0b4..b9393fba4ab0f14992d2fec32b0e1b7f1d4bbdfd 100644
>> --- a/arch/arm/mach-imx/esdctl.c
>> +++ b/arch/arm/mach-imx/esdctl.c
>> @@ -1015,10 +1015,50 @@ resource_size_t imx8m_barebox_earlymem_size(unsigned buswidth)
>>  	return min_t(resource_size_t, SZ_4G - MX8M_DDR_CSD1_BASE_ADDR, size);
>>  }
>>  
>> +static void imx8m_extract_optee_fdto(void)
>> +{
>> +	unsigned int early_fdt_sz, fdto_size;
>> +	void *early_fdt, *fdto_dst;
>> +
>> +	imx_scratch_get_fdt(&early_fdt, &early_fdt_sz);
>> +	/* SCRATCH_FDT_SIZE == 0, e.g. if OP-TEE w/o CFG_DT support is used */
>> +	if (early_fdt_sz == 0)
>> +		return;
>> +
>> +	imx_scratch_get_optee_fdto(&fdto_dst, &fdto_size);
>> +	/* SCRATCH_FDTO_SIZE == 0 if feature (back-channel) is not required */
>> +	if (fdto_size == 0) {
>> +		pr_debug("OP-TEE dest DTBO size == 0, skip extracting\n");
>> +		return;
>> +	}
>> +
>> +	/*
>> +	 * OP-TEE DT handling is really cumbersome. In case an external DT was
>> +	 * supplied, OP-TEE re-use this DT and appends overlays.
>> +	 *
>> +	 * Extract the overlays into a single overlay file to make it easier
>> +	 * to apply these onto the barebox and kernel DT.
>> +	 *
>> +	 * It will become easier once barebox supports the transfer-list
>> +	 * protocol and the protocol itself has overlay-entry support.
>> +	 */
> 
> The problem doesn't seem to be i.MX8M specific, so we'll end up
> duplicating this for other SoCs. Couldn't you do optee_extract_fdto() in
> optee_register_overlay() instead?
> 
> Also we are in PBL here. The device tree is already in the i.MX scratch
> space which is available in barebox proper as well, so you could move
> the code there.

On top of that, we don't have even MMU enabled at this point of time.


> 
>> +	if (optee_extract_fdto(early_fdt, fdto_dst, fdto_size)) {
>> +		pr_warn("Failed to extract OP-TEE FDTO, continue without FDTO\n");
>> +		/*
>> +		 * Don't BUG() because the system may have compile-time config
>> +		 * support
>> +		 */
>> +		return;
>> +	}
>> +
>> +	handoff_data_add(HANDOFF_DATA_BL32_DT_OVL, fdto_dst, fdto_size);
> 
> The overlay isn't used in barebox itself, but only for the Kernel.
> 
> You Could just pick up the overlay from the i.MX scratch space in
> barebox proper and pass it to optee_register_overlay().

Agreed. There seems to be no need to do this in the PBL.

Thanks,
Ahmad

> 
> Sascha
> 
> 

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