stm32mp: The purpose of "!tee_find_device()"

[Alex G.]

On 9/30/20 6:03 PM, Alex G. wrote:
> Hi
> 
> I'm trying to wrap my head around the purpose of the following lines in 
> ft_system_setup():
> 
>      if (!CONFIG_IS_ENABLED(OPTEE) ||
>          !tee_find_device(NULL, NULL, NULL, NULL))
>          stm32_fdt_disable_optee(blob);

Hi! Me again! Do we have a (good) reason for this, or should I submit a 
patch to remove this problematic code?

Alex

> My interpretation is "if optee is not running, delete the FDT node".
> The problem is that tee_find_device() invokes device_probe(). This in 
> turn does an SMC call. This call results in an abort and reboot if optee 
> is not running in the first place.
> 
> So I don't think that tee_find_device() can be used as a check for "Is 
> optee running?". Exhibit B: Outside of mach-stm32mp, tee_find_device() 
> is used to obtain of a _working_ TEE node, not to ask if "is optee 
> running?".
> 
> 
> My problem is that trying to start linux with CONFIG_OPTEE=y will cause 
> the bootm command to crash (log in appendix A):
> 
>      load mmc 0:7 $loadaddr boot/uImage
>      load mmc 0:7 $fdt_addr_r boot/stm32mp157c-dk2.dtb
>      load mmc 0:7 0xc8000000 boot/utee
>      setenv bootm_boot_mode sec
>      bootm 0xc8000000 - $fdt_addr_r
> 
> What is the intent of calling tee_find_device() in an FDT fixup 
> function? Do you have any ideas how to make it not crash (short of 
> commenting out the problem lines) ?
> 
> Alex
> 
> 
> Appendix A: u-boot log after bootm command
> 
> ## Booting kernel from Legacy Image at c8000000 ...
>     Image Name:
>     Created:      2020-09-28  20:58:56 UTC
>     Image Type:   ARM Trusted Execution Environment Kernel Image 
> (uncompressed)
>     Data Size:    349276 Bytes = 341.1 KiB
>     Load Address: fdffffe4
>     Entry Point:  fe000000
>     Verifying Checksum ... OK
>     Loading Kernel Image
> ## Flattened Device Tree blob at c4000000
>     Booting using the fdt blob at 0xc4000000
>     Loading Device Tree to cffef000, end cffff5e2 ... OK
> <BOARD RESETS WITHOUT USER INPUT>
> U-Boot SPL 2020.10-rc4 (Sep 20 2020 - 23:46:47 +0000)
> Model: STMicroelectronics STM32MP157C-DK2 Discovery Board