efi: Set Variable Runtime implementation

[Shantur Rathore]

Hi Ilias,

On Fri, Nov 24, 2023 at 10:50 PM Ilias Apalodimas
<ilias.apalodimas at linaro.org> wrote:
>
> Hi Shantur
>
> On Fri, 24 Nov 2023 at 18:51, Shantur Rathore <i at shantur.com> wrote:
> >
> > Hi Heinrich,
> >
> > I am trying to work out how to enable the SetVariableRT service in
> > U-Boot and came across your patch [1] which initially had the
> > SetVariable RT service enabled in EFI but in the final patch this was
> > removed.
> > I am hoping to implement it on top of the SPI Flash EFI store [2] to
> > be able to set Boot order and boot items from Linux the UEFI way.
> >
> > Can I pick your brain on why it was dropped in the patch?
> > Is there any limitation in SetVariableRT service ?
>
> I recently had a talk about it in Plumbers [0]. Generally speaking, RT
> + hardware owned by the kernel is a very weird combination since you
> can't guarantee exclusive access to the flash or the bus and you have
> to preserve a *lot* of code alive in u-boot.
>
> I'll respond to your v1 patchset and we can discuss details there as well.
>
> [0] https://lpc.events/event/17/contributions/1653/

Thanks for the background and helping me understand the problem.
Makes me wonder how things work in the PC world.
U-boot being only ~1MB, can we not leave it all in memory and maybe
just disable SPI access to Linux.
I might be talking rubbish, just thinking what weird ways it can be worked.

Regards,
Shantur