diff --git a/chip/stm32/dma.c b/chip/stm32/dma.c
index 8325d2edba..fe5bdd55d6 100644
--- a/chip/stm32/dma.c
+++ b/chip/stm32/dma.c
@@ -97,6 +97,13 @@ int dma_start_rx(unsigned channel, unsigned count, void *periph,
 	return 0;
 }
 
+int dma_bytes_done(struct dma_channel *chan, int orig_count)
+{
+	if (!(REG32(&chan->ccr) & DMA_EN))
+		return 0;
+	return orig_count - REG32(&chan->cndtr);
+}
+
 /* Hide this code behind an undefined CONFIG for now */
 #ifdef CONFIG_DMA_TEST
 
diff --git a/chip/stm32/dma.h b/chip/stm32/dma.h
index 81a4e1edd9..caf6c6228a 100644
--- a/chip/stm32/dma.h
+++ b/chip/stm32/dma.h
@@ -117,6 +117,19 @@ int dma_start_rx(unsigned channel, unsigned count, void *periph,
  */
 void dma_disable(unsigned channel);
 
+/**
+ * Get the number of bytes available to read, or number of bytes written
+ *
+ * Since the DMA controller counts downwards, if we know the starting value
+ * we can work out how many bytes have been completed so far.
+ *
+ * @param chan		DMA channel to check (use dma_get_channel())
+ * @param orig_count	Original number of bytes requested on channel
+ * @return number of bytes completed on a channel, or 0 if this channel is
+ *		not enabled
+ */
+int dma_bytes_done(struct dma_channel *chan, int orig_count);
+
 /**
  * Start a previously-prepared dma channel
  *