can: mcp25xxfd: optimize reception of big CanFD frame reception with BRS

In case of predicted DLC=15 and in case at least 33% of those are
sent via BRS be aggressive and use bulk fifo reads to avoid missing
any frames due to releasing FIFOs not as fast as possible.

This would be of most impact when having a 1MHz Can Bus with
a 8MHz data bitrate.

Signed-off-by: Martin Sperl <[email protected]>

drivers/net/can/spi/mcp25xxfd/mcp25xxfd_can.h

@@ -642,6 +642,7 @@ struct mcp25xxfd_can_priv {
 		u64 rx_bulk_read_sizes[RX_BULK_READ_STATS_BINS];
 #define RX_HISTORY_SIZE 32
 		u8 rx_history_dlc[RX_HISTORY_SIZE];
+		u8 rx_history_brs[RX_HISTORY_SIZE];
 		u8 rx_history_index;
 		u32 rx_reads_prefetch_predicted;
 	} stats;

drivers/net/can/spi/mcp25xxfd/mcp25xxfd_can_rx.c

@@ -184,8 +184,10 @@ int mcp25xxfd_can_submit_rx_frame(struct spi_device *spi, int fifo)
 	if (rx->flags & CAN_OBJ_FLAGS_FDF)
 		cpriv->fifos.rx.fd_count++;
 
-	/* add to rx_dlc_history */
+	/* add to rx_history */
 	cpriv->stats.rx_history_dlc[cpriv->stats.rx_history_index] = dlc;
+	cpriv->stats.rx_history_brs[cpriv->stats.rx_history_index] =
+		(rx->flags & CAN_OBJ_FLAGS_BRS) ? CANFD_BRS : 0;
 	cpriv->stats.rx_history_index++;
 	if (cpriv->stats.rx_history_index >= RX_HISTORY_SIZE)
 		cpriv->stats.rx_history_index = 0;
@@ -446,16 +448,13 @@ static int mcp25xxfd_can_read_rx_frame_bulk(struct spi_device *spi,
  * reading multiple rx fifos is a realistic option of optimization
  */
 
-static int mcp25xxfd_can_read_rx_frames_fd(struct spi_device *spi)
+static int mcp25xxfd_can_read_rx_frames_single(struct spi_device *spi,
+					       int prefetch)
 {
 	struct mcp25xxfd_priv *priv = spi_get_drvdata(spi);
 	struct net_device *net = priv->net;
 	struct mcp25xxfd_can_priv *cpriv = netdev_priv(net);
-	int i, fifo, prefetch;
-	int ret;
-
-	/* calculate optimal prefetch to use */
-	prefetch = mcp25xxfd_can_rx_predict_prefetch(net);
+	int i, fifo, ret;
 
 	/* loop all frames */
 	for (i = 0, fifo = cpriv->fifos.rx.start;
@@ -473,13 +472,8 @@ static int mcp25xxfd_can_read_rx_frames_fd(struct spi_device *spi)
 	return 0;
 }
 
-/* right now we only optimize for sd (can2.0) frame case,
- * but in principle it could be also be valuable for CANFD
- * frames when we receive lots of 64 byte packets with BRS set
- * and a big difference between nominal and data bitrates
- */
 static
-int mcp25xxfd_can_read_rx_frames_sd(struct spi_device *spi)
+int mcp25xxfd_can_read_rx_frames_bulk(struct spi_device *spi)
 {
 	struct mcp25xxfd_priv *priv = spi_get_drvdata(spi);
 	struct net_device *net = priv->net;
@@ -516,6 +510,35 @@ int mcp25xxfd_can_read_rx_frames_sd(struct spi_device *spi)
 	return 0;
 }
 
+static int mcp25xxfd_can_read_rx_frames_fd(struct spi_device *spi)
+{
+	struct mcp25xxfd_priv *priv = spi_get_drvdata(spi);
+	struct net_device *net = priv->net;
+	struct mcp25xxfd_can_priv *cpriv = netdev_priv(net);
+	int i, count_dlc15, count_brs, prefetch;
+
+	/* get a prediction on prefetch */
+	prefetch = mcp25xxfd_can_rx_predict_prefetch(net);
+
+	/* if the prefetch is < 64 then just read single */
+	if (prefetch < 64)
+		return mcp25xxfd_can_read_rx_frames_single(spi, prefetch);
+
+	/* check if we have mostly brs frames of those DLC=15 frames */
+	for (i = 0, count_brs = 0, count_dlc15 = 0; i < RX_HISTORY_SIZE; i++)
+		if (cpriv->stats.rx_history_dlc[i] == 15) {
+			count_dlc15++;
+			if (cpriv->stats.rx_history_brs[i])
+				count_brs++;
+		}
+
+	/* if we have at least 33% brs frames then run bulk */
+	if (count_brs > (count_dlc15 / 3))
+		return mcp25xxfd_can_read_rx_frames_bulk(spi);
+	else
+		return mcp25xxfd_can_read_rx_frames_single(spi, prefetch);
+}
+
 int mcp25xxfd_can_read_rx_frames(struct spi_device *spi)
 {
 	struct mcp25xxfd_priv *priv = spi_get_drvdata(spi);
@@ -524,5 +547,5 @@ int mcp25xxfd_can_read_rx_frames(struct spi_device *spi)
 	if (net->mtu == CANFD_MTU)
 		return mcp25xxfd_can_read_rx_frames_fd(spi);
 	else
-		return mcp25xxfd_can_read_rx_frames_sd(spi);
+		return mcp25xxfd_can_read_rx_frames_bulk(spi);
 }