[PATCH v2 4/4] ArmPkg/ArmDmaLib: add support for fixed host-to-device DMA offset

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

Some devices, such as the Raspberry Pi3, have a fixed offset between memory
addresses as seen by the host and as seen by the other bus masters. So add
a new PCD that allows this fixed offset to be recorded, and to be used when
returning device addresses from the DmaLib mapping routines.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
 ArmPkg/ArmPkg.dec                      |  8 ++++++++
 ArmPkg/Library/ArmDmaLib/ArmDmaLib.c   | 20 ++++++++++++++++++--
 ArmPkg/Library/ArmDmaLib/ArmDmaLib.inf |  1 +
 3 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/ArmPkg/ArmPkg.dec b/ArmPkg/ArmPkg.dec
index 3cdb5da3d4f3..090ed9951366 100644
--- a/ArmPkg/ArmPkg.dec
+++ b/ArmPkg/ArmPkg.dec
@@ -134,6 +134,14 @@ [PcdsFixedAtBuild.common]
   gArmTokenSpaceGuid.PcdFdSize|0|UINT32|0x0000002C
   gArmTokenSpaceGuid.PcdFvSize|0|UINT32|0x0000002E
 
+  #
+  # Value to add to a host address to obtain a device address, using
+  # unsigned 64-bit integer arithmetic on both ARM and AArch64. This
+  # means we can rely on truncation on overflow to specify negative
+  # offsets.
+  #
+  gArmTokenSpaceGuid.PcdArmDmaDeviceOffset|0x0|UINT64|0x0000044
+
 [PcdsFixedAtBuild.common, PcdsPatchableInModule.common]
   gArmTokenSpaceGuid.PcdFdBaseAddress|0|UINT64|0x0000002B
   gArmTokenSpaceGuid.PcdFvBaseAddress|0|UINT64|0x0000002D
diff --git a/ArmPkg/Library/ArmDmaLib/ArmDmaLib.c b/ArmPkg/Library/ArmDmaLib/ArmDmaLib.c
index 7321388de63e..1de4a6e5b04f 100644
--- a/ArmPkg/Library/ArmDmaLib/ArmDmaLib.c
+++ b/ArmPkg/Library/ArmDmaLib/ArmDmaLib.c
@@ -37,6 +37,15 @@ typedef struct {
 
 STATIC EFI_CPU_ARCH_PROTOCOL      *mCpu;
 
+STATIC
+PHYSICAL_ADDRESS
+HostToDeviceAddress (
+  IN  PHYSICAL_ADDRESS  HostAddress
+  )
+{
+  return HostAddress + PcdGet64 (PcdArmDmaDeviceOffset);
+}
+
 /**
   Provides the DMA controller-specific addresses needed to access system memory.
 
@@ -80,7 +89,14 @@ DmaMap (
     return EFI_INVALID_PARAMETER;
   }
 
-  *DeviceAddress = ConvertToPhysicalAddress (HostAddress);
+  //
+  // The debug implementation of UncachedMemoryAllocationLib in ArmPkg returns
+  // a virtual uncached alias, and unmaps the cached ID mapping of the buffer,
+  // in order to catch inadvertent references to the cached mapping.
+  // Since HostToDeviceAddress () expects ID mapped input addresses, convert
+  // the host address to an ID mapped address first.
+  //
+  *DeviceAddress = HostToDeviceAddress (ConvertToPhysicalAddress (HostAddress));
 
   // Remember range so we can flush on the other side
   Map = AllocatePool (sizeof (MAP_INFO_INSTANCE));
@@ -127,7 +143,7 @@ DmaMap (
         CopyMem (Buffer, HostAddress, *NumberOfBytes);
       }
 
-      *DeviceAddress = ConvertToPhysicalAddress ((UINTN)Buffer);
+      *DeviceAddress = HostToDeviceAddress (ConvertToPhysicalAddress ((UINTN)Buffer));
       Map->BufferAddress = Buffer;
     } else {
       Map->DoubleBuffer  = FALSE;
diff --git a/ArmPkg/Library/ArmDmaLib/ArmDmaLib.inf b/ArmPkg/Library/ArmDmaLib/ArmDmaLib.inf
index 31de3cfd828c..9b7dad114b18 100644
--- a/ArmPkg/Library/ArmDmaLib/ArmDmaLib.inf
+++ b/ArmPkg/Library/ArmDmaLib/ArmDmaLib.inf
@@ -44,6 +44,7 @@ [Protocols]
 [Guids]
 
 [Pcd]
+  gArmTokenSpaceGuid.PcdArmDmaDeviceOffset
 
 [Depex]
   gEfiCpuArchProtocolGuid
-- 
2.7.4