can: mcp251xfd: tef-path: reduce number of SPI core requests to set UINC bit

Reduce the number of separate SPI core requests when setting the UINC bit in
the TEF FIFO, and instead batch them up into a single SPI core request.

Link: https://lore.kernel.org/r/20201126132144.351154-6-mkl@pengutronix.deTested-by: Thomas Kopp <thomas.kopp@microchip.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c

@@ -340,6 +340,23 @@ static void mcp251xfd_ring_init(struct mcp251xfd_priv *priv)
 	tef_ring->head = 0;
 	tef_ring->tail = 0;
 
+	/* FIFO increment TEF tail pointer */
+	addr = MCP251XFD_REG_TEFCON;
+	val = MCP251XFD_REG_TEFCON_UINC;
+	len = mcp251xfd_cmd_prepare_write_reg(priv, &tef_ring->uinc_buf,
+					      addr, val, val);
+
+	for (j = 0; j < ARRAY_SIZE(tef_ring->uinc_xfer); j++) {
+		struct spi_transfer *xfer;
+
+		xfer = &tef_ring->uinc_xfer[j];
+		xfer->tx_buf = &tef_ring->uinc_buf;
+		xfer->len = len;
+		xfer->cs_change = 1;
+		xfer->cs_change_delay.value = 0;
+		xfer->cs_change_delay.unit = SPI_DELAY_UNIT_NSECS;
+	}
+
 	/* TX */
 	tx_ring = priv->tx;
 	tx_ring->head = 0;
@@ -1231,10 +1248,8 @@ static int
 mcp251xfd_handle_tefif_one(struct mcp251xfd_priv *priv,
 			   const struct mcp251xfd_hw_tef_obj *hw_tef_obj)
 {
-	struct mcp251xfd_tx_ring *tx_ring = priv->tx;
 	struct net_device_stats *stats = &priv->ndev->stats;
 	u32 seq, seq_masked, tef_tail_masked;
-	int err;
 
 	seq = FIELD_GET(MCP251XFD_OBJ_FLAGS_SEQ_MCP2518FD_MASK,
 			hw_tef_obj->flags);
@@ -1255,18 +1270,9 @@ mcp251xfd_handle_tefif_one(struct mcp251xfd_priv *priv,
 					    mcp251xfd_get_tef_tail(priv),
 					    hw_tef_obj->ts);
 	stats->tx_packets++;
-
-	/* finally increment the TEF pointer */
-	err = regmap_update_bits(priv->map_reg, MCP251XFD_REG_TEFCON,
-				 GENMASK(15, 8),
-				 MCP251XFD_REG_TEFCON_UINC);
-	if (err)
-		return err;
-
 	priv->tef->tail++;
-	tx_ring->tail++;
 
-	return mcp251xfd_check_tef_tail(priv);
+	return 0;
 }
 
 static int mcp251xfd_tef_ring_update(struct mcp251xfd_priv *priv)
@@ -1353,6 +1359,40 @@ static int mcp251xfd_handle_tefif(struct mcp251xfd_priv *priv)
 	}
 
  out_netif_wake_queue:
+	len = i;	/* number of handled goods TEFs */
+	if (len) {
+		struct mcp251xfd_tef_ring *ring = priv->tef;
+		struct mcp251xfd_tx_ring *tx_ring = priv->tx;
+		struct spi_transfer *last_xfer;
+
+		tx_ring->tail += len;
+
+		/* Increment the TEF FIFO tail pointer 'len' times in
+		 * a single SPI message.
+		 */
+
+		/* Note:
+		 *
+		 * "cs_change == 1" on the last transfer results in an
+		 * active chip select after the complete SPI
+		 * message. This causes the controller to interpret
+		 * the next register access as data. Temporary set
+		 * "cs_change" of the last transfer to "0" to properly
+		 * deactivate the chip select at the end of the
+		 * message.
+		 */
+		last_xfer = &ring->uinc_xfer[len - 1];
+		last_xfer->cs_change = 0;
+		err = spi_sync_transfer(priv->spi, ring->uinc_xfer, len);
+		last_xfer->cs_change = 1;
+		if (err)
+			return err;
+
+		err = mcp251xfd_check_tef_tail(priv);
+		if (err)
+			return err;
+	}
+
 	mcp251xfd_ecc_tefif_successful(priv);
 
 	if (mcp251xfd_get_tx_free(priv->tx)) {

drivers/net/can/spi/mcp251xfd/mcp251xfd.h

@@ -504,6 +504,9 @@ struct mcp251xfd_tef_ring {
 
 	/* u8 obj_num equals tx_ring->obj_num */
 	/* u8 obj_size equals sizeof(struct mcp251xfd_hw_tef_obj) */
+
+	union mcp251xfd_write_reg_buf uinc_buf;
+	struct spi_transfer uinc_xfer[MCP251XFD_TX_OBJ_NUM_MAX];
 };
 
 struct mcp251xfd_tx_ring {