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

[Christoffer Dall]

On 21 November 2013 07:04, Marc Zyngier <marc.zyngier at arm.com> 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... ;-)
>

I'm curious; why did you need to reinvent a linker?  This was all just
assembly right? Could you not write it as position independent code
and just copy a blob of code and be done with it?

(I'm sure it's not that simple, but I'm curious to know why).

-Christoffer