217 lines
8.5 KiB
Plaintext
217 lines
8.5 KiB
Plaintext
Video DMA Support Design Note
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The video port needs to expose the following apis:
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1) PUBLIC
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BOOLEAN
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VideoPortDoDma(
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IN PVOID HwDeviceExtension,
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IN PVIDEO_REQUEST_PACKET pVrp
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);
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This function:
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a) allocates the MDL associated with the InputBuffer
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contained in the pVrp.
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b) maps the buffers if required by the hardware
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c) flushes the system buffers for cache coherency
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d)computes the number of map registers requested
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and checks that this number satisfies system requirements
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e) saves some parameters needed for subsequent
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Io calls such as the associated virtual MDL address, the
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number of map registers
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f) calls IoAllocateAdapterChannel, providiong a callback which
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builds the scatter gather list.
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Requirements: A mechanism to save the arguments to IoMapTransfer
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and a mechanism to indicate that a DPC is to be scheduled. The
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argments to IoMapTransfer are:
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PADAPTER_OBJECT pAO
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Returned from a call to HalGetAdapter and stored
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in the DEVICE_EXTENSION.
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If the actual transfer is desired, this is non NULL.
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If only the physical address is desired, this parameter
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can be NULL.
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PMDL pMdl
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Extracted from irp returned from
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IoBuildDeviceIoControlRequest. (also possible to get irp
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from IoBuildAsynchronousFsdRequest).
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PVOID pMapRegisterBase
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Allocated via ExAllocatePool from nonpaged pool of length
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dependent on bus type. Filled by Io subsystem via a call
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to HalGetBusData and held in the video ports
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DEVICE_EXTENSION.
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PVOID pCurrentVirtualAddress
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Constructed from LogicalAddress and
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MmGetMdlVirtualAddress(Irp->MdlAddress).
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PULONG pLength
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Pointer to amount to be transferred. Value saved in
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PUBLIC_VIDEO_REQUEST_BLOCK.
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BOOLEAN WriteToDevice
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Always set for video.
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2) PVOID
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VideoPortGetCommonBuffer(
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IN PVOID HwDeviceExtension,
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IN PVIDEO_REQUEST_PACKET pVrp,
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IN ULONG Length,
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OUT PPHYSICAL_ADDRESS pLogicalAddress,
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IN BOOLEAN CacheEnabled
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);
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This routine allows the miniport to allocate a common buffer in
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which to store miniport specific data.
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3) PVOID
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VideoPortGetCommonBuffer(
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IN PVOID HwDeviceExtension,
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IN PVIDEO_REQUEST_PACKET pVrp,
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IN ULONG Length,
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OUT PPHYSICAL_ADDRESS pLogicalAddress,
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IN BOOLEAN CacheEnabled
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);
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This routine allows the miniport to allocate a common buffer in
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which to store miniport specific data. This buffer is visible both to the
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system and the device and appears contiguous to the device.
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In support of each of these functions, the following can be added to the
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DEVICE_EXTENSION video port data structure:
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PVOID MapRegisterBase
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PADAPTER_OBJECT pDmaAdapterObject
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DMA_PARAMETERS FlushDmaParameters
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DMA_PARAMETERS MapTransferParameters
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PHW_DMA_STARTED HwDmaStarted
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BOOLEAN bMapBuffers
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where
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MapRegisterBase is as specified above.
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PADAPTER_OBJECT is defined by Io subsystem
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DMA_PARAMETERS, is of the form
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typedef struct __DMA_PARAMETERS {
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PPUBLIC_VIDEO_REQUEST_BLOCK pVideoRequestBlock;
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PIRP pIrp;
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ULONG DataOffset;
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ULONG VRBFlags;
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PVOID pMapRegisterBase;
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ULONG NumberOfMapRegisters;
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PVOID pLogicalAddress;
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ULONG Length;
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PVOID MdlAddress;
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PVRB_SG pScatterGather;
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VRB_SG SGList[17];
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} DMA_PARAMETERS, *PDMA_PARAMETERS;
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which needs to be a field of the Parameters field of the IrpStack as well
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as a field in the interrupt data owned by the miniport and where
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PPUBLIC_VIDEO_REQUEST_BLOCK may be defined by
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typedef struct __PUBLIC_VIDEO_REQUEST_BLOCK {
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// Private stuff.
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PIRP pIrp;
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ULONG VRBFlags;
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ULONG Qindex;
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// Public stuff.
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VIDEO_REQUEST_PACKET vrp;
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BOOLEAN bUnlock;
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} PUBLIC_VIDEO_REQUEST_BLOCK, *PPUBLIC_VIDEO_REQUEST_BLOCK;
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with VRB_SG defined by
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typedef struct __VRB_SG {
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int64 PhysicalAddress;
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ULONG Length;
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} VRB_SG, *PVRB_SG;
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Useful flags for VRBFlags in DMA_PARAMETERS:
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DMA_FLUSH_ADAPTER
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MAP_DMA_TRANSFER
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FREE_SG
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NOTIFY_REQUIRED.
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Also in PORT_CONFIG_INFO, the following are required:
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ULONG DmaChannel
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ULONG DmaPort
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DMA_WIDTH DmaWidth
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DMA_SPEED DmaSpeed
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BOOLEAN DMA32bitAddresses
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BOOLEAN DMADemandMode
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One of the dependencies that supporting DMA transfers has in NT is calling
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IoAllocateAdapterChannel.
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This routine is of the form:
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NTSTATUS
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IoAllocateAdapterChannel(
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PADAPTER_OBJECT pAO,
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PDEVICE_OBJECT pDO,
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ULONG NumberOfRegisters,
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PDRIVER_CONTROL pBuildScatterGather,
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PVOID pContext
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);
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where pAO is returned by HalGetAdapter,
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pDO is returned by IoCreateDevice
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NumberOfRegisters comes from a calculation involving the
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DataBuffer to be transferred and it's length.
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pBuildScatterGather builds the scatter/gather list and is a
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callback from the Io subsystem.
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pContext is the context pointer passed into pBuildScatterGather
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by Io subsystem (PDMA_PARAMETERS).
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If the miniport has indicated that DMA support is desired, then the
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following sequence of system calls are made:
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MmGetMdlVirtualAddress (to save IoMapTransfer params)
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MmGetSystemAddressForMdl (if MapBuffers set)
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KeFlushIoBuffers
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IoAllocateAdapterChannel (request a DPC if this fails)
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KeSynchronizeExecution
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IoMapTransfer (note PADAPTER_OBJECT)
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IoFlushAdapterBuffers
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IoFreeMapRegisters
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The Io subsystem calls back to a routine to build scatter gather lists
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of the form:
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IO_PRIVATE
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IO_ALLOCATION_ACTION
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pVideoPortBuildScatterGather(
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PDEVICE_OBJECT pDO,
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PIRP pIrp,
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PVOID pMapRegisterBase,
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PVOID pDmaParameters
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);
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As mentioned, it builds and saves the scatter gather lists, and calls
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KeSynchronizeExecution, passing in pVideoPortStartDmaSynchronized as
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the synchronizing function. pVideoPortStartDmaSynchronized in turn calls
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HwStartDma, which is not to return until the device has finished draining
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the current request data.
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IOCTL interface
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IOCTL_VIDEO_DMA_INIT - set by DispDrvr
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Causes VideoPortGetCommonBuffer() to be called by miniport.
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IOCTL_VIDEO_DMA_TRANSFER - set by DispDrvr
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Causes VideoPortDoDma() to be called by miniport.
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VideoPortGetScatterGatherList is called from miniport.
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IOCTL_VIDEO_DMA_UNLOCK_PAGES - set by DispDrvr
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Causes pVideoPortUnlock to be called from videoport. Note that
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this IOCTL is private to the videoport.
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