IODMACommand help needed.

Hi,

 

I am converting the IOMemoryCursor based DMA in my IOKit PCI driver, for my company's PCI interface cards, to use IODMACommand.

I create the IODMACommand instance during driver startup:

 

       queue->MemCmdP = IODMACommand::withSpecification ( &newSegment, 32, 0, IODMACommand::kMapped, 0, 1 );

       if ( (void*)NULL == queue->MemCmdP )

              return ( 0 );

 

I release the IODMACommand during driver shutdown:

 

       if ( (IODMACommand*)NULL != MemCmdP )

              MemCmdP->release ( );

 

Before creating the ScatterGather list I associated the data buffer with the IODMACommand:

 

       MemCmdP->setMemoryDescriptor ( MemDescP );

 

I the call gen32IOVMSegments() to create ScatterGather entries:

 

       TableUsed = 255;

       IOReturn ret = MemCmdP->gen32IOVMSegments ( (UInt64*)&( StartPoint ), (IODMACommand::Segment32 *)Entry, &TableUsed );

       switch ( ret )

       {

              // Yay! Generated segments correctly.

       case kIOReturnSuccess:

              break;

             

              // Lots of possible reasons for failure.

       case kIOReturnOverrun:            IOLog ( "build(): gen32IOVMSegments() returned kIOReturnOverrun\n" );            return ( ret );

       case kIOReturnMessageTooLarge:    IOLog ( "build(): gen32IOVMSegments() returned kIOReturnMessageTooLarge\n" );    return ( ret );

       case kIOReturnNotReady:           IOLog ( "build(): gen32IOVMSegments() returned kIOReturnNotReady\n" );           return ( ret );

       case kIOReturnBadArgument:        IOLog ( "build(): gen32IOVMSegments() returned kIOReturnBadArgument\n" );        return ( ret );

       }

 

       if ( 0L == TableUsed )

              return ( kIOReturnNoMemory );

 

This is the API for my custom Segment function which is provided during IODMACommand:withSpecification() call:

 

bool HWPlot_DmaQueue::newSegment ( IODMACommand *MemCmdP, IODMACommand::Segment64 Segment, void *Segments, UInt32 SegmentIndex )

{

       // Custom ScatterGather list builder function.

 

       IOLog ( "HWPlot_DmaQueue::newSegment(0x%p, [ %ld, %ld ], 0x%p, %ld): - Called\n",

              MemCmdP, (UInt32)Segment.fIOVMAddr, (UInt32)Segment.fLength, Segments, SegmentIndex );

 

       ...

 

       return ( true );

}

 

I Map the data buffer into memory as follows:

           

       Entry->MemDescP = IOMemoryDescriptor::withAddressRange ( (mach_vm_address_t)Entry->Buffer, (mach_vm_size_t)Entry->BuffLen,

  kIODirectionNone, ( hwplot->userClient )->fTask );

       if ( (IOMemoryDescriptor*)NULL == Entry->MemDescP )

              return ( kIOReturnCannotWire );

      

       if ( kIOReturnSuccess != ( Entry->MemDescP )->prepare ( kIODirectionOutIn ) )

       {

              if ( (IOMemoryDescriptor*)NULL != Entry->MemDescP )

                     Entry->MemDescP->release ( );

              return ( kIOReturnCannotWire );

       }

 

I Unmap the data buffer from memory as follows:

 

       if ( (IOMemoryDescriptor*)NULL != Entry->MemDescP )

       {

              result = Entry->MemDescP->complete ( );

              Entry->MemDescP->release ( );

       }

 

My problem is newSegment does not get called so that I can create my ScatterGather list. The Apple sample code uses one of the 9 predefined functions but does NOT demonstrate use of a custom segmenting function, such as I need. Any ideas how I get my segment function called?

I note from the header file IODMACommand.h that the segment function is a C function. Is a static C++ function allowed as it was for IOMemoryCursor?

 

I would expect an ScatterGather list of, worst case, 1 entry per 4k page giving approx 230 entries per 1000Kb.

When I used an IOMemoryCursor I get this behaviour, albeit very slow.

 

With the IODMACommand method I consistently get kIOReturnOverrun errors at 255 entries.

 

What am I missing or doing wrong?

 

I also had linker/loader related errors as I had missing OSDependencies which this list helped me resolve, but these dependencies were not listed anywhere.

 

Thanks,

 

Peter Young

 

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