Re: [RFC PATCH 4/5] hw/i386/acpi-build: Turn off support of PCIe native hot-plug and SHPC in _OSC

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

On Mon, Jul 13, 2020 at 04:56:54PM +0200, Igor Mammedov wrote:
> On Thu,  9 Jul 2020 00:46:14 +0200
> Julia Suvorova <jusual@redhat.com> wrote:
> 
> > Other methods may be used if the system is capable of this and the _OSC bit
> > is set. Disable them explicitly to force ACPI PCI hot-plug use. The older
> > versions will still use PCIe native.

Do we need that later part btw?

> > 
> > Signed-off-by: Julia Suvorova <jusual@redhat.com>
> > ---
> >  hw/i386/acpi-build.c | 12 ++++++++----
> >  1 file changed, 8 insertions(+), 4 deletions(-)
> > 
> > diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> > index 5c5ad88ad6..0e2891c3ea 100644
> > --- a/hw/i386/acpi-build.c
> > +++ b/hw/i386/acpi-build.c
> > @@ -1599,6 +1599,7 @@ static Aml *build_q35_osc_method(AcpiPmInfo *pm)
> >      Aml *method;
> >      Aml *a_cwd1 = aml_name("CDW1");
> >      Aml *a_ctrl = aml_local(0);
> > +    unsigned osc_ctrl;
> >  
> >      method = aml_method("_OSC", 4, AML_NOTSERIALIZED);
> >      aml_append(method, aml_create_dword_field(aml_arg(3), aml_int(0), "CDW1"));
> > @@ -1612,9 +1613,12 @@ static Aml *build_q35_osc_method(AcpiPmInfo *pm)
> >  
> >      /*
> >       * Always allow native PME, AER (no dependencies)
> > -     * Allow SHPC (PCI bridges can have SHPC controller)
> > +     * Need to disable native and SHPC hot-plug to use acpihp
> > +     *
> > +     * PCI Firmware Specification, Revision 3.2

I don't think you have to add a reference as part of this patchset.
The spec in question documents _OSC so it's not a bad idea to
add it, but it's a bit more work, e.g. we generally try to list
the earliest spec that documents the given feature, since
So I suspect this is 3.0 actually.


> seems incomplete, were you going to point to a concrete chapter that requires this change?


It doesn't as such. A better description would be:

/ * Guests seem to generally prefer native hotplug control. As we want them to
  * use ACPI, don't enable it.
  */



> >       */
> > -    aml_append(if_ctx, aml_and(a_ctrl, aml_int(0x1F), a_ctrl));
> > +    osc_ctrl = pm->pcihp_bridge_en ? 0x1C : 0x1F;
> Since you are touching this, how about converting this magic number to
> something more readable?
> i.e.
>             set_bit(ACPI_OSC_SHPC_EN,  osc_ctrl)
>           or
>             osc_ctrl |= BIT(SOME_FEATURE)
> 

... if there is such a macro. If not I suspect it's better as a comment:

	0x10 /* PCI Express Capability Structure control */ |
	0x80 /* PCI Express Advanced Error Reporting control */ |
	0x40 /* PCI Express Native Power Management Events control */



> > +    aml_append(if_ctx, aml_and(a_ctrl, aml_int(osc_ctrl), a_ctrl));
> >  
> >      if_ctx2 = aml_if(aml_lnot(aml_equal(aml_arg(1), aml_int(1))));
> >      /* Unknown revision */
> > @@ -1696,7 +1700,7 @@ build_dsdt(GArray *table_data, BIOSLinker *linker,
> >          aml_append(dev, aml_name_decl("_CID", aml_eisaid("PNP0A03")));
> >          aml_append(dev, aml_name_decl("_ADR", aml_int(0)));
> >          aml_append(dev, aml_name_decl("_UID", aml_int(1)));
> > -        aml_append(dev, build_q35_osc_method());
> > +        aml_append(dev, build_q35_osc_method(pm));
> >          aml_append(sb_scope, dev);
> >          aml_append(dsdt, sb_scope);
> >  
> > @@ -1771,7 +1775,7 @@ build_dsdt(GArray *table_data, BIOSLinker *linker,
> >              if (pci_bus_is_express(bus)) {
> >                  aml_append(dev, aml_name_decl("_HID", aml_eisaid("PNP0A08")));
> >                  aml_append(dev, aml_name_decl("_CID", aml_eisaid("PNP0A03")));
> > -                aml_append(dev, build_q35_osc_method());
> > +                aml_append(dev, build_q35_osc_method(pm));
> >              } else {
> >                  aml_append(dev, aml_name_decl("_HID", aml_eisaid("PNP0A03")));
> >              }