On Thu, 26 Sept 2024 at 10:03, Patrick Rudolph patrick.rudolph@9elements.com wrote:
On Arm platforms that use ACPI they cannot rely on the "spin-table" CPU bringup usually defined in the FDT. Thus implement the 'ACPI Multi-processor Startup for ARM Platforms', also referred to as 'ACPI parking protocol'.
The ACPI parking protocol works similar to the spin-table mechanism, but the specification also covers lots of shortcomings of the spin-table implementations.
Every CPU defined in the ACPI MADT table has it's own 4K page where the spinloop code and the OS mailbox resides. When selected the U-Boot board code must make sure that the secondary CPUs enter u-boot after relocation as well, so that they can enter the spinloop code residing in the ACPI parking protocol pages.
The OS will then write to the mailbox and generate an IPI to release the CPUs from the spinloop code.
For now it's only implemented on ARMv8, but can easily be extended to other platforms, like ARMv7.
TEST: Boots all CPUs on qemu-system-aarch64 -machine raspi4b
Signed-off-by: Patrick Rudolph patrick.rudolph@9elements.com Cc: Simon Glass sjg@chromium.org Cc: Tom Rini trini@konsulko.com
Changelog v2:
- Use shorter function names
- Drop the use of atomics, they do not work on real hardware
- Rewrite code and verify on real hardware that CPUs are spinning inside their parking protocol spin-loop code
Changelog v4:
- Shorten names
- Fix coding style
- Drop extern from the headers
arch/arm/cpu/armv8/Makefile | 1 + arch/arm/cpu/armv8/acpi_park_v8.S | 113 ++++++++++++++++++++++ arch/arm/include/asm/acpi_table.h | 32 +++++++ arch/arm/lib/acpi_table.c | 149 ++++++++++++++++++++++++++++++ include/acpi/acpi_table.h | 10 ++ include/bloblist.h | 1 + lib/Kconfig | 16 ++++ lib/acpi/acpi_table.c | 4 + 8 files changed, 326 insertions(+) create mode 100644 arch/arm/cpu/armv8/acpi_park_v8.S
Reviewed-by: Simon Glass sjg@chromium.org