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

Marc Zyngier
2013-11-22T14:51:56Z

On 22/11/13 08:40, Ian Campbell wrote:
> 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.

Yes, that's what I meant. More. Coffee.

M.
--
Jazz is not dead. It just smells funny...