On Thu, 2013-11-21 at 15:04 +0000, Marc Zyngier wrote:
Hi Rob,
On 21/11/13 14:28, Rob Herring wrote:
On Thu, Nov 21, 2013 at 2:59 AM, Marc Zyngier marc.zyngier@arm.com 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 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.
Interesting. As a separate binary, I'm not sure this belongs or benefits from being in u-boot. I would like to see this as a more generic secure firmware loader or PSCI code be a part of u-boot code directly. With the latter, you could extend it beyond PSCI to things like env variable access (basically equivalent to UEFI runtime services). I'm not saying we should do that though.
So I started this by having something that was actually part of u-boot, and copying itself into SRAM, patching stuff as it went. The net result was that I was reinventing a runtime linker. Needless to say, I gave up quickly... ;-)
What could be done would be for u-boot to be at least partially linked to run from some other region.
Can't you just build and link it as you do now and then link it into the .rodata section of the final u-boot image as a blob to copy out to the defined address at runtime?
That would allow for the secure mode services to be both part of u-boot, and stay resident.
That'd probably be a good thing to have a look at.
BTW, you will need to mark this region reserved in the dtb if in system RAM.
Yes. Eventually, I'd like the psci mode to be entirely generated from u-boot, as well as the eventual RAM reserved.
Did you mean "psci node" here? In which case yes please.
Ian.