dmaengine: Add support for reporting DMA cached data amount

A DMA hardware can have big cache or FIFO and the amount of data sitting in
the DMA fabric can be an interest for the clients.

For example in audio we want to know the delay in the data flow and in case
the DMA have significantly large FIFO/cache, it can affect the latenc/delay

Signed-off-by: Peter Ujfalusi <[email protected]>
Reviewed-by: Tero Kristo <[email protected]>
Tested-by: Keerthy <[email protected]>
Reviewed-by: Grygorii Strashko <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Vinod Koul <[email protected]>

Author: Peter Ujfalusi

drivers/dma/dmaengine.h

@@ -77,6 +77,7 @@ static inline enum dma_status dma_cookie_status(struct dma_chan *chan,
 		state->last = complete;
 		state->used = used;
 		state->residue = 0;
+		state->in_flight_bytes = 0;
 	}
 	return dma_async_is_complete(cookie, complete, used);
 }
@@ -87,6 +88,13 @@ static inline void dma_set_residue(struct dma_tx_state *state, u32 residue)
 		state->residue = residue;
 }
 
+static inline void dma_set_in_flight_bytes(struct dma_tx_state *state,
+					   u32 in_flight_bytes)
+{
+	if (state)
+		state->in_flight_bytes = in_flight_bytes;
+}
+
 struct dmaengine_desc_callback {
 	dma_async_tx_callback callback;
 	dma_async_tx_callback_result callback_result;

include/linux/dmaengine.h

@@ -686,11 +686,13 @@ static inline struct dma_async_tx_descriptor *txd_next(struct dma_async_tx_descr
  * @residue: the remaining number of bytes left to transmit
  *	on the selected transfer for states DMA_IN_PROGRESS and
  *	DMA_PAUSED if this is implemented in the driver, else 0
+ * @in_flight_bytes: amount of data in bytes cached by the DMA.
  */
 struct dma_tx_state {
 	dma_cookie_t last;
 	dma_cookie_t used;
 	u32 residue;
+	u32 in_flight_bytes;
 };
 
 /**