On Tue, Aug 19, 2025 at 10:34:39AM +0000, Uros Stajic wrote: > From: Chao-ying Fu <[email protected]> > > Introduce the 'startharts' command for RISC-V targets, which prints > or executes commands to power up and reset all harts and jump to > 0x80000000. The command supports optional cluster/core count and > immediate execution via the 'g' argument. > > Signed-off-by: Chao-ying Fu <[email protected]> > Signed-off-by: Uros Stajic <[email protected]>
I noticed in OpenSBI, P8700 already implements HSM extension[1], which means it's usually unnecessary to take care of SMP stuff in U-Boot. Do you still want the new startharts command? In summary, there are two possible solutions to support SMP for RISC-V systems with U-Boot and OpenSBI with minimal effort, where SPL runs in M mode and proper U-Boot runs in S mode, 1. Release all the HARTs in SPL stage. With SMP enabled in U-Boot SPL, a core is randomly picked to run the main part of U-Boot SPL, and the others simply spin and wait. When all the initialization and load are finished, an IPI message is sent to each spinning HART, releasing them to the next-level firmware's entry (OpenSBI here), see smp_call_function called in spl_opensbi.c. This is usually more appropriate when your platform releases all HARTs when powered up, in which case you could omit the code of releasing all HARTs to U-Boot SPL. This requires a proper implementation of IPI, and proper description of all HARTs in devicetree. 2. Implement SMP bring-up code totally in OpenSBI. U-Boot itself is expected to run in single thread, so it's unnecessary to bring up any cores in U-Boot. RISC-V SBI defines a HART-State-Management extension (HSM). You could implement HART bring-up code in OpenSBI, and expecting kernel (maybe Linux) brings up the rest HARTs through the extension. Looking through the startharts command, P8700 does require manual steps to release non-boot cores, which makes option 1 less appropriate since it introduces more platform-specific code to U-Boot, while it has been already implemented in OpenSBI, becoming some duplicated code. I suggest moving to HSM extension entirely and avoiding introducing any SMP code in U-Boot for your port. Or, if you still prefer to implement it in U-Boot, please re-use the existing framework of bring up HARTs (smp_call_function, proper IPI, etc.). This could definitely helps code review and future maintenance. Best regards, Yao Zi [1]: https://github.com/riscv-software-src/opensbi/commit/66ab965e54017292d530033ffaae127389c45458
