Re: [Xen-devel] [Qemu-devel] [PATCH v5 12/24] hw: acpi: Export the MCFG getter

[Igor Mammedov <imammedo@xxxxxxxxxx>]

On Thu, 22 Nov 2018 00:21:06 +0100
Samuel Ortiz <sameo@xxxxxxxxxxxxxxx> wrote:

> Hi Igor,
> 
> On Thu, Nov 15, 2018 at 01:36:58PM +0100, Igor Mammedov wrote:
> > On Mon,  5 Nov 2018 02:40:35 +0100
> > Samuel Ortiz <sameo@xxxxxxxxxxxxxxx> wrote:
> >   
> > > From: Yang Zhong <yang.zhong@xxxxxxxxx>
> > > 
> > > The ACPI MCFG getter is not x86 specific and could be called from
> > > anywhere within generic ACPI API, so let's export it.  
> > So far it's x86 or more exactly q35 specific thing,  
> It's property based, and it's using a generic PCIE property afaict.
> So it's up to each machine type to define those properties.
> I'm curious here: What's the idiomatic way to define a machine
> setting/attribute/property, let each instance define it or not, and
> make it available at run time?
> Would you be getting the PCI host pointer from the ACPI build state and
> getting that information back from there?

Cleaner way would be make arm/virt board set PCIE_HOST_MCFG_BASE/
PCIE_HOST_MCFG_SIZE properties and then use common build_mcfg()(in aml-build.c).
Something like this:
  acpi_setup_reduced()
     AcpiMcfgInfo mcfg_info = {
       .base = object_property_get_uint(pcie, PCIE_HOST_MCFG_BASE, NULL),
       .size = object_property_get_uint(pcie, PCIE_HOST_MCFG_SIZE, NULL)
     };
     acpi_build() {
         build_mcfg("MCFG", &info);
     }
  }
and for legacy q35
  acpi_build() {
     if (pcie) {
        AcpiMcfgInfo mcfg_info = {
          .base = object_property_get_uint(pcie, PCIE_HOST_MCFG_BASE, NULL),
          .size = object_property_get_uint(pcie, PCIE_HOST_MCFG_SIZE, NULL)
        };
        if (mcfg_info.base != PCIE_BASE_ADDR_UNMAPPED)
            build_mcfg("MCFG", &info);
        else
            /* move comment here why we are doing it */
            build_mcfg("QEMU", &info);
     }
  }

The thing I don't like about acpi_get_mcfg() is that it
does lookup acpi_get_i386_pci_host() each time it's called
and judges if it's PCI-E host by presence of properties.

I'd rather be explicit where PCI host be fetched once somewhere
in acpi_setup() or possibly passed down from the board as an argument
and board telling to i386/acpi_setup() if it's PCI or PCI-E host
so we don't have to guess it in acpi code.


> Cheers,
> Samuel.


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