WDDM 子设备描述符

子设备的描述信息是能过函数BddDdiQueryDeviceDescriptor实现的。

    InitialData.DxgkDdiQueryDeviceDescriptor        = BddDdiQueryDeviceDescriptor;

严格来说，这个DxgkDdiQueryDeviceDescriptor的回调函数是获取所有设备的描述符信息，这里的设备不仅包括display adapter的子设备，也包括外部连接设备（如连接到display adapter上的监视器monitor)。

当然获取设备描述信息的前提是显卡正常工作，当该驱动已经停止的时候，应返回失败。

NTSTATUS
BddDdiQueryDeviceDescriptor(
    _In_  VOID*                     pDeviceContext,
    _In_  ULONG                     ChildUid,
    _Inout_ DXGK_DEVICE_DESCRIPTOR* pDeviceDescriptor)
{
    PAGED_CODE();
    BDD_ASSERT_CHK(pDeviceContext != NULL);

    BASIC_DISPLAY_DRIVER* pBDD = reinterpret_cast<BASIC_DISPLAY_DRIVER*>(pDeviceContext);
    if (!pBDD->IsDriverActive())
    {
        // During stress testing of PnPStop, it is possible for BDD Fallback to get called to start then stop in quick succession.
        // The first call queues a worker thread item indicating that it now has a child device, the second queues a worker thread
        // item that it no longer has any child device. This function gets called based on the first worker thread item, but after
        // the driver has been stopped. Therefore instead of asserting like other functions, we only warn.
        BDD_LOG_WARNING1("BDD (0x%I64x) is being called when not active!", pBDD);
        return STATUS_UNSUCCESSFUL;
    }
    return pBDD->QueryDeviceDescriptor(ChildUid, pDeviceDescriptor);
}

设备的描述信息主要是设备的EDID信息，这里只支持基本的EDID信息，并不支持扩展EDID信息。

关于EDID的信息，可以参考https://www.cnblogs.com/beyond-rxl/p/9266997.html

// EDID retrieval
NTSTATUS BASIC_DISPLAY_DRIVER::QueryDeviceDescriptor(_In_    ULONG                   ChildUid,
                                                     _Inout_ DXGK_DEVICE_DESCRIPTOR* pDeviceDescriptor)
{
    PAGED_CODE();

    BDD_ASSERT(pDeviceDescriptor != NULL);
    BDD_ASSERT(ChildUid < MAX_CHILDREN);

    // If we haven't successfully retrieved an EDID yet (invalid ones are ok, so long as it was retrieved)
    if (!m_Flags.EDID_Attempted)
    {
        GetEdid(ChildUid);
    }

    if (!m_Flags.EDID_Retrieved || !m_Flags.EDID_ValidHeader || !m_Flags.EDID_ValidChecksum)
    {
        // Report no EDID if a valid one wasn't retrieved
        return STATUS_GRAPHICS_CHILD_DESCRIPTOR_NOT_SUPPORTED;
    }
    else if (pDeviceDescriptor->DescriptorOffset == 0)
    {
        // Only the base block is supported
        RtlCopyMemory(pDeviceDescriptor->DescriptorBuffer,
                      m_EDIDs[ChildUid],
                      min(pDeviceDescriptor->DescriptorLength, EDID_V1_BLOCK_SIZE));

        return STATUS_SUCCESS;
    }
    else
    {
        return STATUS_MONITOR_NO_MORE_DESCRIPTOR_DATA;
    }
}