Re: [Qemu-devel] [RFC][PATCH 2/2] xen:i386:pc_piix: create isa bridge specific to IGD passthrough

[Chen, Tiejun]

On 2014/11/5 22:09, Michael S. Tsirkin wrote:
> On Wed, Nov 05, 2014 at 03:22:59PM +0800, Tiejun Chen wrote:
> > Currently IGD drivers always need to access PCH by 1f.0, and
> > PCH vendor/device id is used to identify the card.
> >
> > Signed-off-by: Tiejun Chen <address@hidden>
> > ---
> >   hw/i386/pc_piix.c | 28 +++++++++++++++++++++++++++-
> >   1 file changed, 27 insertions(+), 1 deletion(-)
> >
> > diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
> > index b559181..b19c7a9 100644
> > --- a/hw/i386/pc_piix.c
> > +++ b/hw/i386/pc_piix.c
> > @@ -50,7 +50,7 @@
> >   #include "cpu.h"
> >   #include "qemu/error-report.h"
> >   #ifdef CONFIG_XEN
> > -#  include <xen/hvm/hvm_info_table.h>
> > +#include <xen/hvm/hvm_info_table.h>
> >   #endif
> >
> >   #define MAX_IDE_BUS 2
> > @@ -452,6 +452,31 @@ static void pc_init_isa(MachineState *machine)
> >   }
> >
> >   #ifdef CONFIG_XEN
> > +static void xen_igd_passthrough_isa_bridge_create(PCIBus *bus)
> > +{
> > +    struct PCIDevice *dev;
> > +    Error *local_err = NULL;
> > +    uint16_t device_id = 0xffff;
> > +
> > +    /* Currently IGD drivers always need to access PCH by 1f.0. */
> > +    dev = pci_create_simple(bus, PCI_DEVFN(0x1f, 0),
> > +                            "xen-igd-passthrough-isa-bridge");
> > +
> > +    /* Identify PCH card with its own real vendor/device ids.
> > +     * Here that vendor id is always PCI_VENDOR_ID_INTEL.
> > +     */
> > +    if (dev) {
> > +        device_id = object_property_get_int(OBJECT(dev), "device-id",
> > +                                            &local_err);
> > +        if (!local_err && device_id != 0xffff) {
> > +            pci_config_set_device_id(dev->config, device_id);
> > +            return;
> > +        }
> > +    }
> > +
> > +    fprintf(stderr, "xen set xen-igd-passthrough-isa-bridge failed\n");
> > +}
> > +
> >   static void pc_xen_hvm_init(MachineState *machine)
> >   {
> >       PCIBus *bus;
> > @@ -461,6 +486,7 @@ static void pc_xen_hvm_init(MachineState *machine)
> >       bus = pci_find_primary_bus();
> >       if (bus != NULL) {
> >           pci_create_simple(bus, -1, "xen-platform");
> > +        xen_igd_passthrough_isa_bridge_create(bus);
> >       }
> >   }
> >   #endif
>
> Can't we defer this step until the GPU is added?

Sounds great but I can't figure out where we can to do this exactly.

> This way there won't be need to poke at host device
> directly, you could get all info from dev->config
> of the host device.

As I understand We have two steps here:

#1 At first I have to write something to check if we're registering 
00:02.0 & IGD, right? But where? While registering each pci device?

#2 Then if that condition is matched, we register this ISA bridge on its 
associated bus.

Thanks
Tiejun

> Additionally the correct bridge would be initialized automatically.
>
>
> > --
> > 1.9.1