efivars

[Greg KH]

On Thu, Sep 23, 2021 at 05:38:27AM -0400, Ruben Safir wrote:
> > Instead the OS needs UEFI runtime services to talk to the platform
> > firmware. 
> 
> What is that?  The kernel is on the Metal.  It is talking directly to
> the hardware.

No it is not.  It is turtles all the way down, sorry.

> > (obviously there is much more than simply
> > shutting down). How can an OS know that you've attached a plug and play
> > device if it cannot talk to the platform firmware?
> > 
> What are you talking about?  The Kernel doesn't need UEFI to know a
> device is attached and to autoload a kernel module and talk to it.

Yes it does.

> It causes an interupt and announces itself on the systembus.

What do you mean exactly by "systembus"?  I have never heard of such a
thing.

> What do you think those thousands of hardware choices are about when you 
> compile the kernel?

Those are options that the kernel can enable/disable support for and
have nothing to do with how the kernel can find those devices in the
system.

> BIOS systems can do that 100%.

As I stated before, UEFI is just the newer standard of BIOS.

> And then there is other hardware, like
> ARM.

UEFI runs on many ARM systems.

Those that do not use UEFI rely on device trees to get information for
what the system looks like and how to talk to it.  x86 systems do not
use device tree, sorry.

> It is useless to for me to argue what I would want to have happen.  I
> have no say and nobody cares about my opinion.  I do want to know what
> it is doing, though, and why I can't install a UEFI boot system from a
> thumdrive that loads in BIOS mode.

Because those are two different standards.

greg k-h