Re: [Qemu-devel] [Linaro-acpi] [RFC PATCH 0/7] hw/arm/virt: Dynamic ACPI v5.1 table generation

[Mark Rutland <mark.rutland@arm.com>]

[...]

> > > > > We are currently suggesting adding an RDSP property to the chosen node
> > > > > in the tiny DT, but a command-line arguement like kexec proposed could
> > > > > be another option I guess, albeit not a very pretty one.
> > > > 
> > > > I'm not sure what an RDSP command line property would have to do with
> > > > kexec. I'll assume I've misunderstood something.
> > > > 
> > > 
> > > I thought the kexec patches proposed passing the RDSP on the
> > > command-line to boot the secondary kernel, so if that ended up being
> > > supported by the kernel for kexec, maybe that could be leveraged by
> > > Xen's boot protocol.  It was an idea someone brought to me, just thought
> > > I'd mention it.
> > 
> > Ah, that's not something I'd heard of.
> 
> Maybe there was a misunderstanding then, I thought you were cc'ed on
> those discussions.

I may just have lost them in my inbox. I'm on a few too many mailing
lists these days. Sorry about that.

> > I'm not a fan of placing fundamentally required system description on
> > the command line. It's fine for explicit overrides but I don't think it
> > should be the default mechanism as that causes its own set of problems
> > (who wants to fight with their hypervisor to pass a command line to a
> > guest kernel?).
> > 
> 
> Agreed completely, but I've been lacking strong technical arguments
> against passing this stuff on the cmdline.  My personal preferred
> approach for the Xen Dom0 case is to add a property to the DT.

Something under /chosen, or a firmware node would sound preferable to
me. For UEFI we pass the system table address as
/chosen/linux,uefi-system-table = <... ...>, and I think the RDSP could
be handled similarly if necessary. The user can than override that via
the command line if desired.

Ideally, the user shouldn't have to place anything on the command line
to get a usable system. Obviously some things will be necesarry (where
is my rootfs?), but that should be the user's configuration of the
system rather than fundamental properties of said system.

The big issue I'm aware of at the moment that forces people to provide a
command line (on non-virtualised systems at least) is the default
console and the rate thereof, but that's being looked into currently.

Thanks,
Mark.