Boot process for optee

BL1 usually be used as bootrom and will pass one argument to Next stage bootloader.

/*******************************************************************************
 * Structure used for telling the next BL how much of a particular type of
 * memory is available for its use and how much is already used.
 ******************************************************************************/
typedef struct meminfo {
    uintptr_t total_base;
    size_t total_size;
} meminfo_t;

BL2 usually be used to load extra images, including BL31, BL32, BL33 etc.
When go to next stage image, it will pass image load information to next stage bootloaders.

Fellowing definition defined the struct format to pass.

/* BL image node in the BL image execution sequence */
typedef struct bl_params_node {
    unsigned int image_id;
    image_info_t *image_info;
    entry_point_info_t *ep_info;
    struct bl_params_node *next_params_info;
} bl_params_node_t;

/*
 * BL image head node in the BL image execution sequence
 * It is also used to pass information to next BL image.
 */
typedef struct bl_params {
    param_header_t h;
    bl_params_node_t *head;
} bl_params_t;

BL31 usually be used as secure monitor, it will be running on the whold system life cycle.
BL31 will pass different arguments from bl_params to next stage images
In BL31 case, It just bypass arguments from bl2 to bl31 in our case.

BL31 initial all runtime service registered using the DECLARE_RT_SVC()
for OPTEE, it will be opteed_setup()
opteed_setup will do:

1. Get secure image ep_info (BL2 will pass it to bl31 via x0).
   
2. arguments for opteed including:
   

   opteed_rw

   OPTEE execution state information i.e. aarch32 or aarch64
   

   opteed_pageable_part

   pass to optee os as arg0
   

   opteed_mem_limit

   pass to optee os as arg1
   

   dt_addr

   pass to optee os as arg2
   

opteed register fellowing fastcall, and it's usage is shown as fellowing.

calling optee_vector_table->fast_smc_entry

There is no handler in bl31 to handle yield call, bl31 only bypass this request to S-EL1.
calling optee_vector_table->yield_smc_entry

For information about optee image
https://optee.readthedocs.io/en/latest/architecture/core.html#pager
in our case, qemu aarch64 don't use pager, and only use paged image.
optee os main images: optee_os/out/arm/core/tee-pager_v2.bin

OPTEE service entry point

1. init exception vector table.
   
2. clear bss section
   
3. setup stack pointer.
   
4. dcache invalidation
   
5. console initialize
   
6. mmu initialize
   
7. optee thread init
   
8. setup nonsec memory
   
9. add optee service node to device-tree
   
10. config console driver according to device-tree
    
11. init gic
    
12. dcache clean & invalidation
    
13. Call smc return to Secure Monitor
    

Finally, system will return a service vectory table to secure monitor.
From now, optee os boot complete.