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

["Chen, Tiejun" <tiejun.chen@intel.com>]

On 2014/6/25 14:45, Michael S. Tsirkin wrote:
> 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.

I guess these stubs are left to extend something in the future. But 
maybe we can remove them now.

>
>> +
>> +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. */
>

Good comments so thanks so much.

>
>> +    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?

This is a real ISA bridge.

> So why does it make sense to get it's vendor/device/revision and
> stick in the ISA bridge?

The Intel generation of integrated graphics needs to probe this ISA 
bridge to initialize the i915 driver properly.

Thanks
Tiejun

>
> 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
>
>