Add support for partial free of non cached buffers.
If a request for less than the full size is requested new allocations
for the remaining head and tail of the buffer are added to the list.
The XHCI driver does this if the page size for the controller is >4KB.

Signed-off-by: Jeff Brasen <jbrasen@nvidia.com>
---
 .../NonDiscoverablePciDeviceIo.c              | 48 ++++++++++++++++++-
 1 file changed, 46 insertions(+), 2 deletions(-)

diff --git a/MdeModulePkg/Bus/Pci/NonDiscoverablePciDeviceDxe/NonDiscoverablePciDeviceIo.c b/MdeModulePkg/Bus/Pci/NonDiscoverablePciDeviceDxe/NonDiscoverablePciDeviceIo.c
index c1c5c6267c..858d953acf 100644
--- a/MdeModulePkg/Bus/Pci/NonDiscoverablePciDeviceDxe/NonDiscoverablePciDeviceIo.c
+++ b/MdeModulePkg/Bus/Pci/NonDiscoverablePciDeviceDxe/NonDiscoverablePciDeviceIo.c
@@ -960,12 +960,18 @@ NonCoherentPciIoFreeBuffer (
   LIST_ENTRY                                   *Entry;
   EFI_STATUS                                   Status;
   NON_DISCOVERABLE_DEVICE_UNCACHED_ALLOCATION  *Alloc;
+  NON_DISCOVERABLE_DEVICE_UNCACHED_ALLOCATION  *AllocHead;
+  NON_DISCOVERABLE_DEVICE_UNCACHED_ALLOCATION  *AllocTail;
   BOOLEAN                                      Found;
+  UINTN                                        StartPages;
+  UINTN                                        EndPages;
 
   Dev = NON_DISCOVERABLE_PCI_DEVICE_FROM_PCI_IO (This);
 
   Found = FALSE;
   Alloc = NULL;
+  AllocHead = NULL;
+  AllocTail = NULL;
 
   //
   // Find the uncached allocation list entry associated
@@ -976,9 +982,13 @@ NonCoherentPciIoFreeBuffer (
        Entry = Entry->ForwardLink)
   {
     Alloc = BASE_CR (Entry, NON_DISCOVERABLE_DEVICE_UNCACHED_ALLOCATION, List);
-    if ((Alloc->HostAddress == HostAddress) && (Alloc->NumPages == Pages)) {
+    StartPages = 0;
+    if (Alloc->HostAddress < HostAddress) {
+      StartPages = (HostAddress - Alloc->HostAddress) / EFI_PAGE_SIZE;
+    }
+    if ((Alloc->HostAddress <= HostAddress) && (Alloc->NumPages >= (Pages + StartPages))) {
       //
-      // We are freeing the exact allocation we were given
+      // We are freeing at least part of what we were given
       // before by AllocateBuffer()
       //
       Found = TRUE;
@@ -991,7 +1001,41 @@ NonCoherentPciIoFreeBuffer (
     return EFI_NOT_FOUND;
   }
 
+  EndPages = Alloc->NumPages - (Pages + StartPages);
+
+  if (StartPages != 0) {
+    AllocHead = AllocatePool (sizeof *AllocHead);
+    if (AllocHead == NULL) {
+      return EFI_OUT_OF_RESOURCES;
+    }
+
+    AllocHead->HostAddress = Alloc->HostAddress;
+    AllocHead->NumPages = StartPages;
+    AllocHead->Attributes = Alloc->Attributes;
+  }
+
+  if (EndPages != 0) {
+    AllocTail = AllocatePool (sizeof *AllocTail);
+    if (AllocTail == NULL) {
+      return EFI_OUT_OF_RESOURCES;
+    }
+
+    AllocTail->HostAddress = Alloc->HostAddress + ((Pages + StartPages) * EFI_PAGE_SIZE);
+    AllocTail->NumPages = EndPages;
+    AllocTail->Attributes = Alloc->Attributes;
+  }
+
   RemoveEntryList (&Alloc->List);
+  //
+  // Record this new sub allocations in the linked list, so we
+  // can restore the memory space attributes later
+  //
+  if (AllocHead != NULL) {
+    InsertHeadList (&Dev->UncachedAllocationList, &AllocHead->List);
+  }
+  if (AllocTail != NULL) {
+    InsertHeadList (&Dev->UncachedAllocationList, &AllocTail->List);
+  }
 
   Status = gDS->SetMemorySpaceAttributes (
                   (EFI_PHYSICAL_ADDRESS)(UINTN)HostAddress,
-- 
2.17.1



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