Re: [Qemu-devel] [v5][PATCH 2/5] xen, gfx passthrough: create pseudo intel isa bridge

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

On Wed, Jun 25, 2014 at 10:17:18AM +0800, Tiejun Chen wrote:
> ISA bridge is needed since Intel gfx drive will probe with Dev31:Fun0
> to make graphics device passthrough work well for VMM, that only need
> to expose this pseudo ISA bridge to let driver know the real hardware
> underneath.
> 
> The original patch is from Allen Kay <allen.m.kay@intel.com>
> 
> Signed-off-by: Yang Zhang <yang.z.zhang@Intel.com>
> Signed-off-by: Tiejun Chen <tiejun.chen@intel.com>
> Cc: Allen Kay <allen.m.kay@intel.com>
> ---
> v5:
> 
> * Don't set this ISA class property, instead, just fake this ISA bridge
>   with 00:1f.0. 
> 
> v4:
> 
> * Remove some unnecessary "return" in void foo().
> 
> v3:
> 
> * Fix some typos.
> * Improve some return paths.
> 
> v2:
> 
> * Nothing is changed.
> 
>  hw/xen/xen_pt_graphics.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 61 insertions(+)
> 
> diff --git a/hw/xen/xen_pt_graphics.c b/hw/xen/xen_pt_graphics.c
> index 461e526..974b7e9 100644
> --- a/hw/xen/xen_pt_graphics.c
> +++ b/hw/xen/xen_pt_graphics.c
> @@ -230,3 +230,64 @@ out:
>      g_free(bios);
>      return rc;
>  }
> +
> +static uint32_t isa_bridge_read_config(PCIDevice *d, uint32_t addr, int len)
> +{
> +    return pci_default_read_config(d, addr, len);
> +}
> +
> +static void isa_bridge_write_config(PCIDevice *d, uint32_t addr, uint32_t v,
> +                                    int len)
> +{
> +    pci_default_write_config(d, addr, v, len);
> +}
> +
> +static void isa_bridge_class_init(ObjectClass *klass, void *data)
> +{
> +    PCIDeviceClass *k = PCI_DEVICE_CLASS(klass);
> +
> +    k->config_read = isa_bridge_read_config;
> +    k->config_write = isa_bridge_write_config;
> +};

You don't need these stubs, just don't fill anything,
pci core will use defaults then.

> +
> +typedef struct {
> +    PCIDevice dev;
> +} ISABridgeState;
> +

Nor do you need an empty structure if it has no state.

> +static TypeInfo isa_bridge_info = {
> +    .name          = "pseudo-intel-pch-isa-bridge",
> +    .parent        = TYPE_PCI_DEVICE,
> +    .instance_size = sizeof(ISABridgeState),
> +    .class_init = isa_bridge_class_init,
> +};
> +
> +static void xen_pt_graphics_register_types(void)
> +{
> +    type_register_static(&isa_bridge_info);
> +}
> +
> +type_init(xen_pt_graphics_register_types)
> +
> +static int create_pseudo_pch_isa_bridge(PCIBus *bus, XenHostPCIDevice *hdev)
> +{
> +    struct PCIDevice *dev;
> +
> +    char rid;
> +
> +    /* We havt to use a simple PCI device to fake this ISA bridge
> +     * to avoid making some confusion to BIOS and ACPI.
> +     */

A typo and confusing wording above, I'm not really
sure what this comment means.
Maybe:

/* Create a fake ISA bridge device at the location expected by guests. */


> +    dev = pci_create(bus, PCI_DEVFN(0x1f, 0), "pseudo-intel-pch-isa-bridge");
> +
> +    qdev_init_nofail(&dev->qdev);
> +
> +    pci_config_set_vendor_id(dev->config, hdev->vendor_id);
> +    pci_config_set_device_id(dev->config, hdev->device_id);
> +
> +    xen_host_pci_get_block(hdev, PCI_REVISION_ID, (uint8_t *)&rid, 1);

Host PCI device is the VGA card?
So why does it make sense to get it's vendor/device/revision and
stick in the ISA bridge?

Also change rid to uint8_t, you won't need to cast then.

> +
> +    pci_config_set_revision(dev->config, rid);
> +
> +    XEN_PT_LOG(dev, "The pseudo Intel PCH ISA bridge created.\n");
> +    return 0;
> +}
> -- 
> 1.9.1