[edk2-devel] [PATCH edk2-platforms v3 4/5] Silicon/Broadcom/BcmGenetDxe: avoid uncached memory for streaming DMA

[Ard Biesheuvel]

The non-coherent version of DmaAllocateBuffer () returns uncached
memory, to ensure that the CPU and the device see the same data,
even we they are accessing the buffer at the same time.

This is not really necessary for our RX ring: the CPU never accesses
the buffer while it is mapped for writing by the device, and so we
can simply use the streaming DMA model, which uses ordinary cached
buffers, but issues a cache invalidate at DMA unmap time.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel at arm.com>
---
 Silicon/Broadcom/Drivers/Net/BcmGenetDxe/BcmGenetDxe.inf |  4 ++++
 Silicon/Broadcom/Drivers/Net/BcmGenetDxe/GenetUtil.c     | 18 +++++++++++++-----
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/Silicon/Broadcom/Drivers/Net/BcmGenetDxe/BcmGenetDxe.inf b/Silicon/Broadcom/Drivers/Net/BcmGenetDxe/BcmGenetDxe.inf
index e74fa02ad209..3cabc5936562 100644
--- a/Silicon/Broadcom/Drivers/Net/BcmGenetDxe/BcmGenetDxe.inf
+++ b/Silicon/Broadcom/Drivers/Net/BcmGenetDxe/BcmGenetDxe.inf
@@ -49,3 +49,7 @@ [Protocols]
   gBcmGenetPlatformDeviceProtocolGuid         ## TO_START
   gEfiDevicePathProtocolGuid                  ## BY_START
   gEfiSimpleNetworkProtocolGuid               ## BY_START
+
+[Pcd]
+  gEmbeddedTokenSpaceGuid.PcdDmaDeviceOffset
+  gEmbeddedTokenSpaceGuid.PcdDmaDeviceLimit
diff --git a/Silicon/Broadcom/Drivers/Net/BcmGenetDxe/GenetUtil.c b/Silicon/Broadcom/Drivers/Net/BcmGenetDxe/GenetUtil.c
index 746fbfe51b1d..23bd1c1d2baa 100644
--- a/Silicon/Broadcom/Drivers/Net/BcmGenetDxe/GenetUtil.c
+++ b/Silicon/Broadcom/Drivers/Net/BcmGenetDxe/GenetUtil.c
@@ -19,6 +19,10 @@
 
 #define GENET_PHY_RETRY     1000
 
+STATIC CONST
+EFI_PHYSICAL_ADDRESS   mDmaAddressLimit = FixedPcdGet64 (PcdDmaDeviceLimit) -
+                                          FixedPcdGet64 (PcdDmaDeviceOffset);
+
 /**
   Read a memory-mapped device CSR.
 
@@ -605,16 +609,20 @@ GenetDmaAlloc (
   IN GENET_PRIVATE_DATA *Genet
   )
 {
-  EFI_STATUS  Status;
-  UINTN       Idx;
+  EFI_PHYSICAL_ADDRESS    Address;
+  EFI_STATUS              Status;
+  UINTN                   Idx;
 
   for (Idx = 0; Idx < GENET_DMA_DESC_COUNT; Idx++) {
-    Status = DmaAllocateBuffer (EfiBootServicesData, EFI_SIZE_TO_PAGES (GENET_MAX_PACKET_SIZE), (VOID **)&Genet->RxBuffer[Idx]);
+    Address = mDmaAddressLimit;
+    Status = gBS->AllocatePages (AllocateMaxAddress, EfiBootServicesData,
+                    EFI_SIZE_TO_PAGES (GENET_MAX_PACKET_SIZE), &Address);
     if (EFI_ERROR (Status)) {
       DEBUG ((DEBUG_ERROR, "GenetDmaAlloc: Failed to allocate RX buffer: %r\n", Status));
       GenetDmaFree (Genet);
       return Status;
     }
+    Genet->RxBuffer[Idx] = (UINT8 *)(UINTN)Address;
   }
 
   return EFI_SUCCESS;
@@ -699,8 +707,8 @@ GenetDmaFree (
     GenetDmaUnmapRxDescriptor (Genet, Idx);
 
     if (Genet->RxBuffer[Idx] != NULL) {
-      DmaFreeBuffer (EFI_SIZE_TO_PAGES (GENET_MAX_PACKET_SIZE),
-        Genet->RxBuffer[Idx]);
+      gBS->FreePages ((UINTN)Genet->RxBuffer[Idx],
+        EFI_SIZE_TO_PAGES (GENET_MAX_PACKET_SIZE));
       Genet->RxBuffer[Idx] = NULL;
     }
   }
-- 
2.17.1


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