can: xilinx_can: refactor code in preparation for CAN FD support

Xilinx CAN FD cores are different enough from the previous Zynq and AXI
CAN cores that some refactoring of the driver is needed.

This commit contains most of the required refactoring to existing code
and should not alter behavior on existing supported HW.

The changes are:

- Reading and writing to frame registers is parametrized to allow
  reading/writing a different frame in the future.

- Slightly misleading (as it did not specify *all* the interrupts
  supported by the HW) XCAN_INTR_ALL is replaced with specifying the
  interrupts inline in interrupt enabling code.

- xcan_devtype_data.caps is renamed to xcan_devtype_data.flags to allow
  for flags that define alternative functionality (e.g. mailboxes vs.
  FIFO) instead of purely additive capabilities.

- can_bittiming_const is added to xcan_devtype_data as CAN FD cores will
  have wider setting ranges.

- bus_clk clock name is now determined through xcan_devtype_data instead
  of comparing compatible string in probe().

- xcan_devtype_data is added to xcan_priv to allow flag checks after
  probe().

- XCAN_CAP_WATERMARK is now XCAN_FLAG_TXFEMP. CAN FD cores have
  watermark support but no TXFEMP interrupt, which is what we are
  actually interested in.

- xcan_start_xmit() is split to in two parts to prepare for TX mailboxes
  instead of FIFO in CAN FD cores.

v2: Wrapped some long lines in xcan_write_frame().

Signed-off-by: Anssi Hannula <anssi.hannula@bitwise.fi>
Cc: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/xilinx_can.c

@@ -51,16 +51,15 @@ enum xcan_reg {
 	XCAN_ISR_OFFSET		= 0x1C, /* Interrupt status */
 	XCAN_IER_OFFSET		= 0x20, /* Interrupt enable */
 	XCAN_ICR_OFFSET		= 0x24, /* Interrupt clear */
-	XCAN_TXFIFO_ID_OFFSET	= 0x30,/* TX FIFO ID */
-	XCAN_TXFIFO_DLC_OFFSET	= 0x34, /* TX FIFO DLC */
-	XCAN_TXFIFO_DW1_OFFSET	= 0x38, /* TX FIFO Data Word 1 */
-	XCAN_TXFIFO_DW2_OFFSET	= 0x3C, /* TX FIFO Data Word 2 */
-	XCAN_RXFIFO_ID_OFFSET	= 0x50, /* RX FIFO ID */
-	XCAN_RXFIFO_DLC_OFFSET	= 0x54, /* RX FIFO DLC */
-	XCAN_RXFIFO_DW1_OFFSET	= 0x58, /* RX FIFO Data Word 1 */
-	XCAN_RXFIFO_DW2_OFFSET	= 0x5C, /* RX FIFO Data Word 2 */
+	XCAN_TXFIFO_OFFSET	= 0x30, /* TX FIFO base */
+	XCAN_RXFIFO_OFFSET	= 0x50, /* RX FIFO base */
 };
 
+#define XCAN_FRAME_ID_OFFSET(frame_base)	((frame_base) + 0x00)
+#define XCAN_FRAME_DLC_OFFSET(frame_base)	((frame_base) + 0x04)
+#define XCAN_FRAME_DW1_OFFSET(frame_base)	((frame_base) + 0x08)
+#define XCAN_FRAME_DW2_OFFSET(frame_base)	((frame_base) + 0x0C)
+
 /* CAN register bit masks - XCAN_<REG>_<BIT>_MASK */
 #define XCAN_SRR_CEN_MASK		0x00000002 /* CAN enable */
 #define XCAN_SRR_RESET_MASK		0x00000001 /* Soft Reset the CAN core */
@@ -101,11 +100,6 @@ enum xcan_reg {
 #define XCAN_IDR_RTR_MASK		0x00000001 /* Remote TX request */
 #define XCAN_DLCR_DLC_MASK		0xF0000000 /* Data length code */
 
-#define XCAN_INTR_ALL		(XCAN_IXR_TXOK_MASK | XCAN_IXR_BSOFF_MASK |\
-				 XCAN_IXR_WKUP_MASK | XCAN_IXR_SLP_MASK | \
-				 XCAN_IXR_RXNEMP_MASK | XCAN_IXR_ERROR_MASK | \
-				 XCAN_IXR_RXOFLW_MASK | XCAN_IXR_ARBLST_MASK)
-
 /* CAN register bit shift - XCAN_<REG>_<BIT>_SHIFT */
 #define XCAN_BTR_SJW_SHIFT		7  /* Synchronous jump width */
 #define XCAN_BTR_TS2_SHIFT		4  /* Time segment 2 */
@@ -118,6 +112,15 @@ enum xcan_reg {
 #define XCAN_FRAME_MAX_DATA_LEN		8
 #define XCAN_TIMEOUT			(1 * HZ)
 
+/* TX-FIFO-empty interrupt available */
+#define XCAN_FLAG_TXFEMP	0x0001
+
+struct xcan_devtype_data {
+	unsigned int flags;
+	const struct can_bittiming_const *bittiming_const;
+	const char *bus_clk_name;
+};
+
 /**
  * struct xcan_priv - This definition define CAN driver instance
  * @can:			CAN private data structure.
@@ -133,6 +136,7 @@ enum xcan_reg {
  * @irq_flags:			For request_irq()
  * @bus_clk:			Pointer to struct clk
  * @can_clk:			Pointer to struct clk
+ * @devtype:			Device type specific constants
  */
 struct xcan_priv {
 	struct can_priv can;
@@ -149,6 +153,7 @@ struct xcan_priv {
 	unsigned long irq_flags;
 	struct clk *bus_clk;
 	struct clk *can_clk;
+	struct xcan_devtype_data devtype;
 };
 
 /* CAN Bittiming constants as per Xilinx CAN specs */
@@ -164,11 +169,6 @@ static const struct can_bittiming_const xcan_bittiming_const = {
 	.brp_inc = 1,
 };
 
-#define XCAN_CAP_WATERMARK	0x0001
-struct xcan_devtype_data {
-	unsigned int caps;
-};
-
 /**
  * xcan_write_reg_le - Write a value to the device register little endian
  * @priv:	Driver private data structure
@@ -329,7 +329,11 @@ static int xcan_chip_start(struct net_device *ndev)
 		return err;
 
 	/* Enable interrupts */
-	priv->write_reg(priv, XCAN_IER_OFFSET, XCAN_INTR_ALL);
+	priv->write_reg(priv, XCAN_IER_OFFSET,
+			XCAN_IXR_TXOK_MASK | XCAN_IXR_BSOFF_MASK |
+			XCAN_IXR_WKUP_MASK | XCAN_IXR_SLP_MASK |
+			XCAN_IXR_RXNEMP_MASK | XCAN_IXR_ERROR_MASK |
+			XCAN_IXR_RXOFLW_MASK | XCAN_IXR_ARBLST_MASK);
 
 	/* Check whether it is loopback mode or normal mode  */
 	if (priv->can.ctrlmode & CAN_CTRLMODE_LOOPBACK) {
@@ -390,33 +394,15 @@ static int xcan_do_set_mode(struct net_device *ndev, enum can_mode mode)
 }
 
 /**
- * xcan_start_xmit - Starts the transmission
- * @skb:	sk_buff pointer that contains data to be Txed
- * @ndev:	Pointer to net_device structure
- *
- * This function is invoked from upper layers to initiate transmission. This
- * function uses the next available free txbuff and populates their fields to
- * start the transmission.
- *
- * Return: NETDEV_TX_OK on success and NETDEV_TX_BUSY when the tx queue is full
+ * xcan_write_frame - Write a frame to HW
+ * @skb:		sk_buff pointer that contains data to be Txed
+ * @frame_offset:	Register offset to write the frame to
  */
-static netdev_tx_t xcan_start_xmit(struct sk_buff *skb, struct net_device *ndev)
+static void xcan_write_frame(struct xcan_priv *priv, struct sk_buff *skb,
+			     int frame_offset)
 {
-	struct xcan_priv *priv = netdev_priv(ndev);
-	struct can_frame *cf = (struct can_frame *)skb->data;
 	u32 id, dlc, data[2] = {0, 0};
-	unsigned long flags;
-
-	if (can_dropped_invalid_skb(ndev, skb))
-		return NETDEV_TX_OK;
-
-	/* Check if the TX buffer is full */
-	if (unlikely(priv->read_reg(priv, XCAN_SR_OFFSET) &
-			XCAN_SR_TXFLL_MASK)) {
-		netif_stop_queue(ndev);
-		netdev_err(ndev, "BUG!, TX FIFO full when queue awake!\n");
-		return NETDEV_TX_BUSY;
-	}
+	struct can_frame *cf = (struct can_frame *)skb->data;
 
 	/* Watch carefully on the bit sequence */
 	if (cf->can_id & CAN_EFF_FLAG) {
@@ -452,23 +438,42 @@ static netdev_tx_t xcan_start_xmit(struct sk_buff *skb, struct net_device *ndev)
 	if (cf->can_dlc > 4)
 		data[1] = be32_to_cpup((__be32 *)(cf->data + 4));
 
+	priv->write_reg(priv, XCAN_FRAME_ID_OFFSET(frame_offset), id);
+	/* If the CAN frame is RTR frame this write triggers transmission */
+	priv->write_reg(priv, XCAN_FRAME_DLC_OFFSET(frame_offset), dlc);
+	if (!(cf->can_id & CAN_RTR_FLAG)) {
+		priv->write_reg(priv, XCAN_FRAME_DW1_OFFSET(frame_offset),
+				data[0]);
+		/* If the CAN frame is Standard/Extended frame this
+		 * write triggers transmission
+		 */
+		priv->write_reg(priv, XCAN_FRAME_DW2_OFFSET(frame_offset),
+				data[1]);
+	}
+}
+
+/**
+ * xcan_start_xmit_fifo - Starts the transmission (FIFO mode)
+ *
+ * Return: 0 on success, -ENOSPC if FIFO is full.
+ */
+static int xcan_start_xmit_fifo(struct sk_buff *skb, struct net_device *ndev)
+{
+	struct xcan_priv *priv = netdev_priv(ndev);
+	unsigned long flags;
+
+	/* Check if the TX buffer is full */
+	if (unlikely(priv->read_reg(priv, XCAN_SR_OFFSET) &
+			XCAN_SR_TXFLL_MASK))
+		return -ENOSPC;
+
 	can_put_echo_skb(skb, ndev, priv->tx_head % priv->tx_max);
 
 	spin_lock_irqsave(&priv->tx_lock, flags);
 
 	priv->tx_head++;
 
-	/* Write the Frame to Xilinx CAN TX FIFO */
-	priv->write_reg(priv, XCAN_TXFIFO_ID_OFFSET, id);
-	/* If the CAN frame is RTR frame this write triggers tranmission */
-	priv->write_reg(priv, XCAN_TXFIFO_DLC_OFFSET, dlc);
-	if (!(cf->can_id & CAN_RTR_FLAG)) {
-		priv->write_reg(priv, XCAN_TXFIFO_DW1_OFFSET, data[0]);
-		/* If the CAN frame is Standard/Extended frame this
-		 * write triggers tranmission
-		 */
-		priv->write_reg(priv, XCAN_TXFIFO_DW2_OFFSET, data[1]);
-	}
+	xcan_write_frame(priv, skb, XCAN_TXFIFO_OFFSET);
 
 	/* Clear TX-FIFO-empty interrupt for xcan_tx_interrupt() */
 	if (priv->tx_max > 1)
@@ -480,6 +485,35 @@ static netdev_tx_t xcan_start_xmit(struct sk_buff *skb, struct net_device *ndev)
 
 	spin_unlock_irqrestore(&priv->tx_lock, flags);
 
+	return 0;
+}
+
+/**
+ * xcan_start_xmit - Starts the transmission
+ * @skb:	sk_buff pointer that contains data to be Txed
+ * @ndev:	Pointer to net_device structure
+ *
+ * This function is invoked from upper layers to initiate transmission. This
+ * function uses the next available free txbuff and populates their fields to
+ * start the transmission.
+ *
+ * Return: NETDEV_TX_OK on success and NETDEV_TX_BUSY when the tx queue is full
+ */
+static int xcan_start_xmit(struct sk_buff *skb, struct net_device *ndev)
+{
+	int ret;
+
+	if (can_dropped_invalid_skb(ndev, skb))
+		return NETDEV_TX_OK;
+
+	ret = xcan_start_xmit_fifo(skb, ndev);
+
+	if (ret < 0) {
+		netdev_err(ndev, "BUG!, TX full when queue awake!\n");
+		netif_stop_queue(ndev);
+		return NETDEV_TX_BUSY;
+	}
+
 	return NETDEV_TX_OK;
 }
 
@@ -487,13 +521,14 @@ static netdev_tx_t xcan_start_xmit(struct sk_buff *skb, struct net_device *ndev)
  * xcan_rx -  Is called from CAN isr to complete the received
  *		frame  processing
  * @ndev:	Pointer to net_device structure
+ * @frame_base:	Register offset to the frame to be read
  *
  * This function is invoked from the CAN isr(poll) to process the Rx frames. It
  * does minimal processing and invokes "netif_receive_skb" to complete further
  * processing.
  * Return: 1 on success and 0 on failure.
  */
-static int xcan_rx(struct net_device *ndev)
+static int xcan_rx(struct net_device *ndev, int frame_base)
 {
 	struct xcan_priv *priv = netdev_priv(ndev);
 	struct net_device_stats *stats = &ndev->stats;
@@ -508,9 +543,9 @@ static int xcan_rx(struct net_device *ndev)
 	}
 
 	/* Read a frame from Xilinx zynq CANPS */
-	id_xcan = priv->read_reg(priv, XCAN_RXFIFO_ID_OFFSET);
-	dlc = priv->read_reg(priv, XCAN_RXFIFO_DLC_OFFSET) >>
-				XCAN_DLCR_DLC_SHIFT;
+	id_xcan = priv->read_reg(priv, XCAN_FRAME_ID_OFFSET(frame_base));
+	dlc = priv->read_reg(priv, XCAN_FRAME_DLC_OFFSET(frame_base)) >>
+				   XCAN_DLCR_DLC_SHIFT;
 
 	/* Change Xilinx CAN data length format to socketCAN data format */
 	cf->can_dlc = get_can_dlc(dlc);
@@ -533,8 +568,8 @@ static int xcan_rx(struct net_device *ndev)
 	}
 
 	/* DW1/DW2 must always be read to remove message from RXFIFO */
-	data[0] = priv->read_reg(priv, XCAN_RXFIFO_DW1_OFFSET);
-	data[1] = priv->read_reg(priv, XCAN_RXFIFO_DW2_OFFSET);
+	data[0] = priv->read_reg(priv, XCAN_FRAME_DW1_OFFSET(frame_base));
+	data[1] = priv->read_reg(priv, XCAN_FRAME_DW2_OFFSET(frame_base));
 
 	if (!(cf->can_id & CAN_RTR_FLAG)) {
 		/* Change Xilinx CAN data format to socketCAN data format */
@@ -806,7 +841,7 @@ static int xcan_rx_poll(struct napi_struct *napi, int quota)
 
 	isr = priv->read_reg(priv, XCAN_ISR_OFFSET);
 	while ((isr & XCAN_IXR_RXNEMP_MASK) && (work_done < quota)) {
-		work_done += xcan_rx(ndev);
+		work_done += xcan_rx(ndev, XCAN_RXFIFO_OFFSET);
 		priv->write_reg(priv, XCAN_ICR_OFFSET, XCAN_IXR_RXNEMP_MASK);
 		isr = priv->read_reg(priv, XCAN_ISR_OFFSET);
 	}
@@ -1193,13 +1228,21 @@ static const struct dev_pm_ops xcan_dev_pm_ops = {
 };
 
 static const struct xcan_devtype_data xcan_zynq_data = {
-	.caps = XCAN_CAP_WATERMARK,
+	.flags = XCAN_FLAG_TXFEMP,
+	.bittiming_const = &xcan_bittiming_const,
+	.bus_clk_name = "pclk",
+};
+
+static const struct xcan_devtype_data xcan_axi_data = {
+	.flags = 0,
+	.bittiming_const = &xcan_bittiming_const,
+	.bus_clk_name = "s_axi_aclk",
 };
 
 /* Match table for OF platform binding */
 static const struct of_device_id xcan_of_match[] = {
 	{ .compatible = "xlnx,zynq-can-1.0", .data = &xcan_zynq_data },
-	{ .compatible = "xlnx,axi-can-1.00.a", },
+	{ .compatible = "xlnx,axi-can-1.00.a", .data = &xcan_axi_data },
 	{ /* end of list */ },
 };
 MODULE_DEVICE_TABLE(of, xcan_of_match);
@@ -1219,7 +1262,7 @@ static int xcan_probe(struct platform_device *pdev)
 	struct net_device *ndev;
 	struct xcan_priv *priv;
 	const struct of_device_id *of_id;
-	int caps = 0;
+	const struct xcan_devtype_data *devtype = &xcan_axi_data;
 	void __iomem *addr;
 	int ret, rx_max, tx_max, tx_fifo_depth;
 
@@ -1241,12 +1284,8 @@ static int xcan_probe(struct platform_device *pdev)
 		goto err;
 
 	of_id = of_match_device(xcan_of_match, &pdev->dev);
-	if (of_id) {
-		const struct xcan_devtype_data *devtype_data = of_id->data;
-
-		if (devtype_data)
-			caps = devtype_data->caps;
-	}
+	if (of_id && of_id->data)
+		devtype = of_id->data;
 
 	/* There is no way to directly figure out how many frames have been
 	 * sent when the TXOK interrupt is processed. If watermark programming
@@ -1259,7 +1298,7 @@ static int xcan_probe(struct platform_device *pdev)
 	 * sent), which is not a sensible state - possibly TXFWMEMP is not
 	 * completely synchronized with the rest of the bits?
 	 */
-	if (caps & XCAN_CAP_WATERMARK)
+	if (devtype->flags & XCAN_FLAG_TXFEMP)
 		tx_max = min(tx_fifo_depth, 2);
 	else
 		tx_max = 1;
@@ -1271,13 +1310,14 @@ static int xcan_probe(struct platform_device *pdev)
 
 	priv = netdev_priv(ndev);
 	priv->dev = &pdev->dev;
-	priv->can.bittiming_const = &xcan_bittiming_const;
+	priv->can.bittiming_const = devtype->bittiming_const;
 	priv->can.do_set_mode = xcan_do_set_mode;
 	priv->can.do_get_berr_counter = xcan_get_berr_counter;
 	priv->can.ctrlmode_supported = CAN_CTRLMODE_LOOPBACK |
 					CAN_CTRLMODE_BERR_REPORTING;
 	priv->reg_base = addr;
 	priv->tx_max = tx_max;
+	priv->devtype = *devtype;
 	spin_lock_init(&priv->tx_lock);
 
 	/* Get IRQ for the device */
@@ -1295,22 +1335,12 @@ static int xcan_probe(struct platform_device *pdev)
 		ret = PTR_ERR(priv->can_clk);
 		goto err_free;
 	}
-	/* Check for type of CAN device */
-	if (of_device_is_compatible(pdev->dev.of_node,
-				    "xlnx,zynq-can-1.0")) {
-		priv->bus_clk = devm_clk_get(&pdev->dev, "pclk");
-		if (IS_ERR(priv->bus_clk)) {
-			dev_err(&pdev->dev, "bus clock not found\n");
-			ret = PTR_ERR(priv->bus_clk);
-			goto err_free;
-		}
-	} else {
-		priv->bus_clk = devm_clk_get(&pdev->dev, "s_axi_aclk");
-		if (IS_ERR(priv->bus_clk)) {
-			dev_err(&pdev->dev, "bus clock not found\n");
-			ret = PTR_ERR(priv->bus_clk);
-			goto err_free;
-		}
+
+	priv->bus_clk = devm_clk_get(&pdev->dev, devtype->bus_clk_name);
+	if (IS_ERR(priv->bus_clk)) {
+		dev_err(&pdev->dev, "bus clock not found\n");
+		ret = PTR_ERR(priv->bus_clk);
+		goto err_free;
 	}
 
 	priv->write_reg = xcan_write_reg_le;