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.mach...@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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