Hi Yusuf,

I hope you have gone through https://trustedfirmware-a.readthedocs.io/en/latest/getting_started/porting-guide.html?highlight=secondary%20core#handling-reset

  1. Distinguishing between a cold boot and a warm boot.

  2. In the case of a cold boot and the CPU being a secondary CPU, ensuring that the CPU is placed in a platform-specific state until the primary CPU performs the necessary steps to remove it from this state.

  3. In the case of a warm boot, ensuring that the CPU jumps to a platform- specific address in the BL31 image in the same processor mode as it was when released from reset.

Secondary cores are kept in TF-A holding pen until primary core makes a request to start secondary core(from OS through PSCI CPU_ON). On receiving this call primary breaks the condition which held secondary. For example, investigate a5ds platform's plat_secondary_cold_boot_setup() & a5ds_pwr_domain_on(). Platform also provides warm_boot_entrypoint (most platform uses bl31_warm_entrypoint) from where secondary starts execution.

Primary core is responsible for platform initialization using platform helper functions mentioned https://trustedfirmware-a.readthedocs.io/en/latest/getting_started/porting-guide.html?highlight=secondary%20core#boot-loader-stage-3-1-bl31 (make sure your platform has implemented all the mandatory hooks).

Hope this helps

thanks
Manish


From: Mohd Yusuf Abdul Hamid via TF-A <tf-a@lists.trustedfirmware.org>
Sent: 07 February 2022 02:32
To: tf-a@lists.trustedfirmware.org <tf-a@lists.trustedfirmware.org>
Subject: [TF-A] How secondary core(s) move from TF-A into Kernel space using PSCI - 4 x A55 ?
 
Hi,
I have been stuck at this problem for more than a week. Hopefully good folks here can help clarify a few things.

Platform 4x Cortex A55 single cluster.

What I got working:
1. I can boot single core kernel to shell using TFA bl31
    Baremetal (bare minimum startup + platform specific SOC enablement, EL3) -> TFA bl31 -> Kernel
2. I added PSCI in DT and can see the hook trigger service and hotplug secondary core in.

Secondary core woke up:
1. Bare minimum startup (skip SOC specific enablement) -> TFA bl31 -> go thru 'plat_secondary_cold_boot_setup' path, using 'RESET_TO_BL31:=1' 

Now, I am not sure how from there, the secondary core would jump to:
a. If jump to kernel's 'secondary_holding_pen' it looks like it would drop from EL3 -> EL1 and wait (however at this point Core0 is already in cpu_idle) and won't continue
    a.1 For this case, I am also not sure why I hit "instruction abort" in core1 - from what I read MMU hasnt been set up, which is true. I also wonder at what point MMU is set up for this path in the secondary core?

b. If jump to 'secondary_entry' I believe the core is still in EL3 at this point and I will get an exception at 'set_cpu_boot_mode_flag'

c. If someone can summarize what are the minimum requirements for the secondary core to get set up before jumping to 'secondary_holding_pen'/'secondary_entry' whichever is applicable.

Any pointers would be much appreciated.

ps: I have access to Trace32.

Mohd Yusuf Abdul Hamid