PSCI is an ARM standard that provides a generic interface that supervisory software can use to manage power in the following situations: - Core idle management - CPU hotplug - big.LITTLE migration models - System shutdown and reset
It basically allows the kernel to offload these tasks to the firmware, and rely on common kernel side code.
More importantly, it gives a way to ensure that CPUs enter the kernel at the appropriate exception level (ie HYP mode, to allow the use of the virtualization extensions), even across events like CPUs being powered off/on or suspended.
The main idea here is to reuse some of the existing u-boot code to create a separate blob that can live in SRAM (or a reserved page of memory), containing a secure monitor that will implement the PSCI operations. This code will still be alive when u-boot is long gone, hence the need for a piece of memory that will not be touched by the OS.
This patch series contains 3 parts: - the first four patches are just bug fixes - the next three contain the generic PSCI code and build infrastructure - the last two implement the CPU_ON method of the Allwinner A20 (aka sun7i).
I realize the A20 u-boot code is not upstream yet (BTW is anyone actively working on that?), but hopefully that should give a good idea of how things are structured so far. The patches are against a merge of u-boot mainline and the sunxi tree as of ten days ago.
As for using this code, it goes like this: sun7i# ext2load mmc 0:1 0x40000000 /boot/sunxi-psci.bin 908 bytes read in 18 ms (48.8 KiB/s) sun7i# cp 0x40000000 0x4000 0x1000 sun7i# ext2load mmc 0:1 40008000 /boot/zImage 3415087 bytes read in 184 ms (17.7 MiB/s) sun7i# setenv bootargs console=ttyS0,115200 earlyprintk root=/dev/nfs nfsroot=10.1.203.35:/export/roots/bobby-brown,tcp,v3 rw ip=dhcp sun7i# bootz 40008000
The kernel now boots in HYP mode, finds its secondary CPU without any additional SMP code, and runs KVM out of the box. Hopefully, the Xen/ARM guys can do the same fairly easily.
I'm wildly cross-posting this patch series, including to lists I'm not subscribed to. Please keep me on Cc for any comment you may have.
Cheers,
M.
Marc Zyngier (9): ARM: HYP/non-sec: fix alignment requirements for vectors ARM: HYP/non-sec: move switch to non-sec to the last boot phase ARM: HYP/non-sec: add a barrier after setting SCR.NS==1 ARM: non-sec: reset CNTVOFF to zero ARM: HYP/non-sec: add generic ARMv7 PSCI code ARM: HYP/non-sec: make pen code sections depend on !ARMV7_PSCI ARM: HYP/non-sec: add the option for a second-stage monitor sunxi: HYP/non-sec: add sun7i PSCI backend sunxi: HYP/non-sec: configure CNTFRQ on all CPUs
Makefile | 5 ++ arch/arm/cpu/armv7/Makefile | 4 ++ arch/arm/cpu/armv7/nonsec_virt.S | 21 +++++- arch/arm/cpu/armv7/psci.S | 109 ++++++++++++++++++++++++++++ arch/arm/cpu/armv7/sunxi/Makefile | 3 + arch/arm/cpu/armv7/sunxi/config.mk | 6 +- arch/arm/cpu/armv7/sunxi/psci.S | 119 +++++++++++++++++++++++++++++++ arch/arm/cpu/armv7/sunxi/u-boot-psci.lds | 63 ++++++++++++++++ arch/arm/cpu/armv7/virt-v7.c | 2 + arch/arm/lib/bootm.c | 5 +- include/configs/sun7i.h | 7 ++ psci/Makefile | 67 +++++++++++++++++ 12 files changed, 406 insertions(+), 5 deletions(-) create mode 100644 arch/arm/cpu/armv7/psci.S create mode 100644 arch/arm/cpu/armv7/sunxi/psci.S create mode 100644 arch/arm/cpu/armv7/sunxi/u-boot-psci.lds create mode 100644 psci/Makefile