Re: [Qemu-devel] [PATCH] piix: do not reset APIC base address (0x80) on piix4_reset.

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Dec 18, 2013 at 11:34:14AM -0500, Paolo Bonzini wrote:
> 
> 
> ----- Messaggio originale -----
> > Da: "Michael S. Tsirkin" <mst@redhat.com>
> > A: "marcel a" <marcel.a@redhat.com>
> > Cc: "Paolo Bonzini" <pbonzini@redhat.com>, "Gal Hammer" <ghammer@redhat.com>, seabios@seabios.org,
> > qemu-devel@nongnu.org
> > Inviato: Mercoledì, 18 dicembre 2013 17:33:06
> > Oggetto: Re: [Qemu-devel] [PATCH] piix: do not reset APIC base address (0x80) on piix4_reset.
> > 
> > On Wed, Dec 18, 2013 at 06:27:12PM +0200, Marcel Apfelbaum wrote:
> > > On Wed, 2013-12-18 at 17:22 +0200, Michael S. Tsirkin wrote:
> > > > On Wed, Dec 18, 2013 at 03:22:59PM +0100, Paolo Bonzini wrote:
> > > > > Il 11/12/2013 10:21, Gal Hammer ha scritto:
> > > > > > Fix a bug that was introduced in commit c046e8c4. QEMU fails to
> > > > > > resume from suspend mode (S3).
> > > > > > 
> > > > > > Signed-off-by: Gal Hammer <ghammer@redhat.com>
> > > > > > ---
> > > > > >  hw/acpi/piix4.c | 1 -
> > > > > >  1 file changed, 1 deletion(-)
> > > > > > 
> > > > > > diff --git a/hw/acpi/piix4.c b/hw/acpi/piix4.c
> > > > > > index 93849c8..5c736a4 100644
> > > > > > --- a/hw/acpi/piix4.c
> > > > > > +++ b/hw/acpi/piix4.c
> > > > > > @@ -376,7 +376,6 @@ static void piix4_reset(void *opaque)
> > > > > >      pci_conf[0x5b] = 0;
> > > > > >  
> > > > > >      pci_conf[0x40] = 0x01; /* PM io base read only bit */
> > > > > > -    pci_conf[0x80] = 0;
> > > > > >  
> > > > > >      if (s->kvm_enabled) {
> > > > > >          /* Mark SMM as already inited (until KVM supports SMM). */
> > > > > 
> > > > > Note this is not the APIC base address, that one is 80h on the ISA
> > > > > bridge (function 0).  You're changing the behavior for 80h on the power
> > > > > management function, which is function 3.  The register is "PMBA—POWER
> > > > > MANAGEMENT BASE ADDRESS" and it is indeed initialized by SeaBIOS in
> > > > > piix4_pm_setup (src/fw/pciinit.c).
> > > > > 
> > > > > Michael, perhaps a part of pci_setup (same file) should run on S3
> > > > > resume?
> > > > > 
> > > > > Paolo
> > > > 
> > > > Seems reasonable: either seabios or guest OS must do it, and
> > > > guest does not seem to.
> > > I was looking into this today, but it seems that we have a problem.
> > > We cannot run pci_setup() in init section:
> > > .data.varinit.seabios/src/hw/pci.h.66 is VARVERIFY32INIT but used from
> > > ['.text.runtime.seabios/src/resume.c.150', '.text.pci_setup']
> > > 
> > > Any thoughts how to get around this?
> > > Thanks,
> > > Marcel
> > 
> > We defintely don't want to do full pci enumeration.
> > Just pci_bios_init_platform or even less.
> 
> Or put an array of (bdf, offset, size, value) tuples somewhere in low memory,
> fill it at startup, and reproduce it blindly at S3 resume time.  This is similar
> to what UEFI does.
> 
> Paolo

Yes, it's an option. Though reworking pci_bios_init_devices so that it
can work from low memory seems easier.