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I have posted a part of this question earlier. Just to be in context I will copy some of the information from that.
I am writing a very simple driver where the application will send me a read and/or write buffer (DMA from and to the device). The device needs a circular buffer for issuing request and completing request (NVME style queues). There can be more than one request issues to the device (4K requests). These requests transfer data to / from the user mode application buffers.
The DMA profile that I am going to use is
WdfDmaProfileScatterGather64Duplex : The device supports packet-based, scatter/gather DMA operations, using 64-bit addressing. The device also supports duplex operation.
From what I have read so far, the following is the flow, when I am using the Windows (KMDF) DMA Abstraction.
Add Device : Create the queues using the common buffer DMA APIs. To use Windows DMA abstraction, create a single DMA enabler object.
EvtIoxxx : Create and Initialize the DMA transaction object.
EvtProgramDma : You will get your SGL, format it to the h/w specific format and then program the hardware for the DMA transfer.
Interrupt calls the DPC
DPC completes the request [one transaction is one transfer]
**My problem is that the documentation states that “ If the driver has specified a packet based DMA profile, it must serialize all of the DMA transactions because the framework allows only one packet based DMA transaction to execute at any given time”. **
I do not understand this statement completely. Does it mean that you can only have a single DMA transfer possible at any given time. That is a sever limitation of DMA Abstraction.
My device will have to have multiple IOs pending at any given time (up to 4K IOs).
If I cannot use the DMA Abstraction APIs, How will I create the SGL? The only option that remains is to walk through the MDL myself and then create the hardware specific SGL in a common buffer. [The Book "Developing Drivers With WDF" says that it is not a good idea to walk the MDL by yourself and build SGL]
Any help is really appreciated.
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