Hi Marc,
On Sat, 15 Feb 2014 13:36:24 +0000, Marc Zyngier marc.zyngier-5wv7dgnIgG8@public.gmane.org wrote:
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 turn some of the existing u-boot code into a separate section that can live in secure RAM (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 4 parts:
- the first four patches are just bug fixes
- the next two refactor the HYP/non-secure code to allow relocation in secure memory
- the next four contain the generic PSCI code and DT infrastructure
- the last three 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 the mainline u-boot tree as of today, merged with the sunxi u-boot tree of the day and the first 10 patches will directly apply to mainline u-boot.
As for using this code, it goes like this: sun7i# ext2load mmc 0:1 0x40008000 zImage ; ext2load mmc 0:1 0x60000000 sun7i-a20-cubietruck.dtb 2270120 bytes read in 117 ms (18.5 MiB/s) 9138 bytes read in 3 ms (2.9 MiB/s) sun7i# fdt addr 0x60000000 ; fdt resize ; fdt set ethernet0 mac-address "[5a fe b0 07 b0 07]" sun7i# setenv bootargs console=ttyS0,115200 earlyprintk ip=dhcp root=/dev/nfs nfsroot=/backup/a20_root,tcp sun7i# bootz 0x40008000 - 0x60000000
The kernel now boots in HYP mode, finds its secondary CPU without any SMP code present in the kernel, and runs KVM out of the box. I've been told the Xen/ARM guys managed to do the same fairly easily.
This code has also been tested on a VExpress TC2, running KVM with all 5 CPUs, in order to make sure there was no obvious regression.
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.
The code is also available at: git://git.kernel.org/pub/scm/linux/kernel/git/maz/u-boot.git wip/psci
Cheers,
M.
Marc, I'm unclear what you want to do with this series. You mention that its first 10 patches will apply to U-Boot, but I am not sure whether you are just indicating that it is possible to apply them or asking for these 10 patches to go in U-Boot mainline. Or is it something else yet?
Amicalement,