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

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

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 <tiejun.chen@intel.com>
> ---
>  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?
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.
Additionally the correct bridge would be initialized automatically.


> -- 
> 1.9.1