Re: [Qemu-devel] [PATCH for-2.10 v2 1/2] hw/acpi: Call acpi_set_pci_info when no ACPI tables needed

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

On Tue, Aug 15, 2017 at 02:07:51PM +0200, Igor Mammedov wrote:
> On Tue, 15 Aug 2017 12:15:48 +0100
> Anthony PERARD <anthony.perard@citrix.com> wrote:
> 
> > To do PCI passthrough with Xen, the property acpi-pcihp-bsel needs to be
> > set, but this was done only when ACPI tables are built which is not
> > needed for a Xen guest. The need for the property starts with commit
> > "pc: pcihp: avoid adding ACPI_PCIHP_PROP_BSEL twice"
> > (f0c9d64a68b776374ec4732424a3e27753ce37b6).
> > 
> > Set pci info before checking for the needs to build ACPI tables.
> > 
> > Assign bsel=0 property only to the root bus on Xen as there is no
> > support in the Xen ACPI tables for a different value.
> 
> looking at hw/acpi/pcihp.c and bsel usage there it looks like
> bsel property is owned by it and not by ACPI tables, so instead of
> shuffling it in acpi_setup(), how about moving bsel initialization
> to hw/acpi/pcihp.c and initialize it there unconditionally?
> 
> It could be as simple as moving acpi_set_pci_info()/acpi_set_bsel()
> there and calling it from acpi_pcihp_reset().
> 
> Then there won't be need for Xen specific branches, as root bus
> will have bsel set automatically which is sufficient for Xen and
> the rest of bsel-s (bridges) will be just unused by Xen,
> which could later extend its ACPI table implementation to utilize them. 

Later is exactly what I'd like to try to avoid.
Whoever wants acpi hotplug for bridges needs to get
the bsel info from qemu supplied acpi tables.

> 
> > Reported-by: Sander Eikelenboom <linux@eikelenboom.it>
> > Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
> > 
> > ---
> > Changes in V2:
> >   - check for acpi_enabled before calling acpi_set_pci_info.
> >   - set the property on the root bus only.
> > 
> > This patch would be a canditade to backport to 2.9.
> > 
> > CC: Stefano Stabellini <sstabellini@kernel.org>
> > CC: Bruce Rogers <brogers@suse.com>
> > ---
> >  hw/i386/acpi-build.c | 25 ++++++++++++++++---------
> >  1 file changed, 16 insertions(+), 9 deletions(-)
> > 
> > diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> > index 98dd424678..c0483b96cf 100644
> > --- a/hw/i386/acpi-build.c
> > +++ b/hw/i386/acpi-build.c
> > @@ -46,6 +46,7 @@
> >  #include "sysemu/tpm_backend.h"
> >  #include "hw/timer/mc146818rtc_regs.h"
> >  #include "sysemu/numa.h"
> > +#include "hw/xen/xen.h"
> >  
> >  /* Supported chipsets: */
> >  #include "hw/acpi/piix4.h"
> > @@ -518,8 +519,13 @@ static void acpi_set_pci_info(void)
> >      unsigned bsel_alloc = ACPI_PCIHP_BSEL_DEFAULT;
> >  
> >      if (bus) {
> > -        /* Scan all PCI buses. Set property to enable acpi based hotplug. */
> > -        pci_for_each_bus_depth_first(bus, acpi_set_bsel, NULL, &bsel_alloc);
> > +        if (xen_enabled()) {
> > +            /* Assign BSEL property to root bus only. */
> > +            acpi_set_bsel(bus, &bsel_alloc);
> > +        } else {
> > +            /* Scan all PCI buses. Set property to enable acpi based hotplug. */
> > +            pci_for_each_bus_depth_first(bus, acpi_set_bsel, NULL, &bsel_alloc);
> > +        }
> >      }
> >  }
> >  
> > @@ -2871,6 +2877,14 @@ void acpi_setup(void)
> >      AcpiBuildState *build_state;
> >      Object *vmgenid_dev;
> >  
> > +    if (!acpi_enabled) {
> > +        ACPI_BUILD_DPRINTF("ACPI disabled. Bailing out.\n");
> > +        return;
> > +    }
> > +
> > +    /* Assign BSEL property on hotpluggable PCI buses. */
> > +    acpi_set_pci_info();
> > +
> >      if (!pcms->fw_cfg) {
> >          ACPI_BUILD_DPRINTF("No fw cfg. Bailing out.\n");
> >          return;
> > @@ -2881,15 +2895,8 @@ void acpi_setup(void)
> >          return;
> >      }
> >  
> > -    if (!acpi_enabled) {
> > -        ACPI_BUILD_DPRINTF("ACPI disabled. Bailing out.\n");
> > -        return;
> > -    }
> > -
> >      build_state = g_malloc0(sizeof *build_state);
> >  
> > -    acpi_set_pci_info();
> > -
> >      acpi_build_tables_init(&tables);
> >      acpi_build(&tables, MACHINE(pcms));
> >