[PATCH 10/10] stm32mp1: spl: Copy optee nodes to target FDT for OP-TEE payloads

[Alex G.]

Hi Patrick,

On 8/31/21 12:24 PM, Patrick DELAUNAY wrote:
> Hi,
> 
> On 8/26/21 11:42 PM, Alexandru Gagniuc wrote:
>> OP-TEE does not take a devicetree for its own use. However, it does
>> pass the devicetree to the normal world OS. In most cases that will
>> be some other devicetree-bearing platform, such as linux.
>>
>> As in other cases where there's an OPTEE payload (e.g. BOOTM_OPTEE),
>> it is required to copy the optee nodes to he target's FDT. Do this as
>> part of spl_board_prepare_for_optee().
>>
>> Signed-off-by: Alexandru Gagniuc <mr.nuke.me at gmail.com>
>> ---
>>   arch/arm/mach-stm32mp/spl.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/arch/arm/mach-stm32mp/spl.c b/arch/arm/mach-stm32mp/spl.c
>> index d9fdc5926c..94fbb45cf9 100644
>> --- a/arch/arm/mach-stm32mp/spl.c
>> +++ b/arch/arm/mach-stm32mp/spl.c
>> @@ -19,6 +19,7 @@
>>   #include <asm/arch/sys_proto.h>
>>   #include <mach/tzc.h>
>>   #include <linux/libfdt.h>
>> +#include <tee/optee.h>
>>   u32 spl_boot_device(void)
>>   {
>> @@ -182,6 +183,7 @@ void stm32_init_tzc_for_optee(void)
>>   void spl_board_prepare_for_optee(void *fdt)
>>   {
>>       stm32_fdt_setup_mac_addr(fdt);
>> +    optee_copy_fdt_nodes(fdt);
>>       stm32_init_tzc_for_optee();
>>   }
> 
> 
> NAK the OP-TEE nodes are ADDED by the OP-TEE firmware in the unsecure 
> device tree (when CFG_DT is activated)
> 
> before to jump to the kernel (that remove the need to have DT 
> allignement with U-Boot SPL device tree)
> 
> => SPL should not copy the OP-TEE nodes in next stage DT
> 
> reference in optee_os = core/arch/arm/kernel/boot.c: add_optee_dt_node()
> 
> add_optee_dt_node() <= update_external_dt() <= paged_init_primary()
> 
> It is the expected configuration for OP-TEE on STM32MP15 platform.

I agree that if a component modifies the platform, it should be 
responsible for updating the devicetree. Two issues though


1. Consistency

The STM32IMAGE boot path expects u-boot to add the optee nodes, while 
the FIP path expects OP-TEE to add the nodes. Which one do we stick to?


2. Memory access

I don't understand is how OP-TEE would get past the TZC.
If we look at optee_os => plat-0stm32mp1/plat_tzc400:
     "Early boot stage is in charge of configuring memory regions"
The following memory has been set up by SPL (or TF-A for that matter):

     Nonsec: c0000000->ddffffff
     Sec:    de000000->dfdfffff
     SHMEM:  dfe00000->dfffffff

The external DTB will be in the nonsec region, which OP-TEE allegedly 
can't access. So how would this get patched?

Alex