[U-Boot] [linux-sunxi] Re: [PATCH 0/9] ARMv7: add PSCI support to u-boot

[Ian Campbell]

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 at 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.