OvmfPkg/VirtioSerialDxe: set EFI_SERIAL_INPUT_BUFFER_EMPTY

Check if there is data available for read, set the
EFI_SERIAL_INPUT_BUFFER_EMPTY flag accordingly.

With proper status returned VirtioSerialIoRead() will only
be called if there is actual data to read, so we must call
VirtioSerialIoWriteFlush() to make sure pending writes get
flushed to the host properly.

Signed-off-by: Gerd Hoffmann <[email protected]>

Author: kraxel

OvmfPkg/VirtioSerialDxe/VirtioSerialPort.c

@@ -157,7 +157,29 @@ VirtioSerialIoGetControl (
   OUT UINT32                 *Control
   )
 {
+  VIRTIO_SERIAL_IO_PROTOCOL  *SerialIo = (VIRTIO_SERIAL_IO_PROTOCOL *)This;
+  BOOLEAN                    HaveData  = FALSE;
+
+  VirtioSerialIoWriteFlush (This);
+
   *Control = 0;
+
+  if (SerialIo->ReadOffset < SerialIo->ReadSize) {
+    // have unread data in current buffer
+    HaveData = TRUE;
+  } else if (VirtioSerialRingHasBuffer (
+               SerialIo->Dev,
+               PortRx (SerialIo->PortId)
+               ))
+  {
+    // have unread buffers in rx ring
+    HaveData = TRUE;
+  }
+
+  if (!HaveData) {
+    *Control |=  EFI_SERIAL_INPUT_BUFFER_EMPTY;
+  }
+
   return EFI_SUCCESS;
 }