Re: DMA Buffer write operation not persisted

[Rafael Machado <rafaelrodrigues.machado@gmail.com>]

Hi Andrew

Thanks for the answer.

The allocation was done at other part of the code. But yet, I used the
PciI->AllocateBuffer() function.

One question, about the topics retrieved from the spec.
When the spec says "• The common buffer can now be accessed equally by the
processor and the DMA bus master."

Does this means that I can write some data using a simple pointer, like for
example copying some data using MemCopy? Or should I still use the
PciIo->Mem.Write...?

I'll really this part of the spec carefully.

Thanks and Regards
Rafael R. Machado

Em qui, 25 de jan de 2018 às 17:04, Andrew Fish <afish@apple.com> escreveu:

> Rafeal,
>
> There are some good summaries in the UEFI Spec that really help.
>
> DMA Bus Master Common Buffer Operation
> • Call AllocateBuffer() to allocate a common buffer.
> • Call Map() for EfiPciOperationBusMasterCommonBuffer or
> EfiPciOperationBusMasterCommonBuffer64.
> • Program the DMA Bus Master with the DeviceAddress returned by Map().
> • The common buffer can now be accessed equally by the processor and the
> DMA bus master.
> • Call Unmap().
> • Call FreeBuffer().
>
> Did you miss the PciIo->AllocateBuffer() call?
>
> For x86 it can abstract things like DMA only supported < 4GB.
> For ARM it may need to change the cacheability of the region etc.
>
> Thanks,
>
> Andrew Fish
>
> > On Jan 25, 2018, at 10:53 AM, Rafael Machado <
> rafaelrodrigues.machado@gmail.com> wrote:
> >
> > Hi everyone.
> >
> > I'm currently work on a task, and I need to write some data at a DMA
> buffer.
> > At the UEFI Driver Writer's guide, at page 359 there is a sample code of
> > how to do that.
> >
> > Considering that code and adapting to my scenario I got the following
> > function (some debug prints are present for clarification):
> >
> > EFI_STATUS
> > EFIAPI
> > DoBusMasterWrite (
> >  IN EFI_PCI_ROOT_BRIDGE_IO_PROTOCOL *PciIo,
> >  IN UINT8 *HostAddress,
> >  IN UINTN *Length,
> >  IN UINT32 Value
> > )
> > {
> >  EFI_STATUS Status;
> >  UINTN NumberOfBytes;
> >  EFI_PHYSICAL_ADDRESS DeviceAddress;
> >  VOID *Mapping;
> >  UINT64 ReadValue;
> >
> >  //
> >  // Call Map() to retrieve the DeviceAddress to use for the bus
> >  // master write operation. The Map() function may not support
> >  // performing a DMA operation for the entire length, so it may
> >  // be broken up into smaller DMA operations.
> >  //
> >  NumberOfBytes = *Length;
> >  Status = PciIo->Map (PciIo, // This
> >
> > EfiPciIoOperationBusMasterCommonBuffer, // Operation
> >                                     (VOID *)HostAddress, // HostAddress
> >                                     &NumberOfBytes, // NumberOfBytes
> >                                     &DeviceAddress, //DeviceAddress
> >                                     &Mapping //Mapping);
> >
> >  if (EFI_ERROR (Status)) {
> >    return Status;
> >  }
> >
> >  //
> >  // Write the data to the desired address
> >  // This write operation also starts the DMA transaction
> >  //
> >  Status = PciIo->Mem.Write (PciIo, // This
> >                                               EfiPciIoWidthUint32, //
> Width
> >                                               *HostAddress,
> >                                               1, // Count
> >                                               &Value // Buffer
> >                                               );
> >
> >  Print(L"NumberOfBytes: %d\r\n", NumberOfBytes);
> >  Print(L"address: 0x%x\r\n", HostAddress);
> >  Print(L"Value: 0x%x\r\n", Value);
> >  Print(L"Status: %r\r\n", Status);
> >
> >  if (EFI_ERROR (Status)) {
> > return Status;
> >  }
> >
> >  //
> >  // The operations performed by PollMem() also flush all posted
> >  // writes from the PCI bus master and through PCI-to-PCI bridges.
> >  //
> >  Status = PciIo->PollMem (PciIo, // This
> >                                               EfiPciIoWidthUint32, //
> Width
> >                                               *HostAddress, // Offset
> >                                               0xFFFFFFFF,// Mask
> >                                               Value,// Value
> >                                               EFI_TIMER_PERIOD_SECONDS
> > (1), // Timeout
> >                                               &ReadValue // Result
> >                                               );
> >  Print(L"Status2: %r\r\n", Status);
> >
> >  if (EFI_ERROR (Status)) {
> > return Status;
> >  }
> >
> >  //
> >  // Call Flush() to flush all write transactions to system memory
> >  //
> >  Status = PciIo->Flush (PciIo);
> >  Print(L"Status3: %r\r\n", Status);
> >
> >  if (EFI_ERROR (Status)) {
> > return Status;
> >  }
> >
> >  //
> >  // Call Unmap() to complete the bus master write operation
> >  //
> >  Status = PciIo->Unmap (PciIo, Mapping);
> >  Print(L"Status4: %r\r\n", Status);
> >
> >  if (EFI_ERROR (Status)) {
> > return Status;
> >  }
> >  return Status;
> > }
> >
> > The output of this function is this:
> >  NumberOfBytes: 4
> >  address: 0xCCCAC000
> >  Value: 0xAAAAA
> >  Status: Success
> >  Status2: Success
> >  Status3: Success
> >  Status4: Success
> >
> > The problem is that when I try to read this memory content using the dmem
> > command at the efiShell the value 0xAAAAA cannot be found. Seems
> something
> > is locking the DMA trasaction.
> > Can someone give me some light?
> >
> > Thanks and Regard
> > Rafael R. Machado
> > _______________________________________________
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>
>