Re: [Qemu-devel] [Qemu-ppc] [PATCH RFC] spapr: by-pass SLOF when -kernel is provided

[Greg Kurz <groug@kaod.org>]

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On Wed, 6 Jul 2016 13:33:49 +1000
Alexey Kardashevskiy <aik@ozlabs.ru> wrote:

> On 06/07/16 11:35, David Gibson wrote:
> > On Tue, Jul 05, 2016 at 04:42:37PM +0200, Laurent Vivier wrote:  
> >> As device-tree is now fully built by QEMU, we don't need SLOF
> >> anymore if the kernel is provided on the command line.
> >>
> >> In this case, don't load SLOF and boot directly into the
> >> kernel.
> >>
> >> This saves at least 5 seconds on the boot sequence.
> >>
> >> Signed-off-by: Laurent Vivier <lvivier@redhat.com>  
> > 
> > I'm not comfortable applying this.  We actually used to do this ages
> > ago, but changed to always running through SLOF, and there were
> > reasons for doing so.
> > 
> > I don't remember exactly what they were, but I think it boiled down to
> > slight differences in state between booting from SLOF and booting
> > without SLOF leading to confusing errors from the guest kernel.
> >   
> 
> PCI resource allocation is still done by SLOF (however having them not set
> will trigger allocation in the guest but this is rather unexpected
> workaround than a feature); "client-architecture-support" won't work
> without SLOF either (i.e. compatibile PowerISA 2.0x CPUs).
> 

Not even sure the workaround actually works:

I retried with a ppc64le guest and this time I get:

[    1.055922] virtio-pci 0000:00:01.0: virtio_pci: leaving for legacy driver
[    1.056048] virtio-pci: probe of 0000:00:01.0 failed with error -12
[    1.056263] virtio-pci 0000:00:00.0: virtio_pci: leaving for legacy driver
[    1.056373] virtio-pci: probe of 0000:00:00.0 failed with error -12

i.e. virtio_reset() isn't called during probing :-\

--
Greg

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