[PATCH V2 2/2] can: xilinx_can: Add Transmitter delay compensation (TDC) feature support

[Srinivas Neeli]

Added Transmitter delay compensation (TDC) feature support.
In the case of higher measured loop delay with higher baud rates,
observed bit stuff errors. By enabling the TDC feature in a controller,
will compensate for the measure loop delay in the receive path.

Signed-off-by: Srinivas Neeli <srinivas.neeli@xxxxxxxxxx>
---
 drivers/net/can/xilinx_can.c | 46 +++++++++++++++++++++++++++++++++---
 1 file changed, 43 insertions(+), 3 deletions(-)

diff --git a/drivers/net/can/xilinx_can.c b/drivers/net/can/xilinx_can.c
index e179d311aa28..d0edd1bca33c 100644
--- a/drivers/net/can/xilinx_can.c
+++ b/drivers/net/can/xilinx_can.c
@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 /* Xilinx CAN device driver
  *
- * Copyright (C) 2012 - 2014 Xilinx, Inc.
+ * Copyright (C) 2012 - 2022 Xilinx, Inc.
  * Copyright (C) 2009 PetaLogix. All rights reserved.
  * Copyright (C) 2017 - 2018 Sandvik Mining and Construction Oy
  *
@@ -99,6 +99,7 @@ enum xcan_reg {
 #define XCAN_ESR_STER_MASK		0x00000004 /* Stuff error */
 #define XCAN_ESR_FMER_MASK		0x00000002 /* Form error */
 #define XCAN_ESR_CRCER_MASK		0x00000001 /* CRC error */
+#define XCAN_SR_TDCV_MASK		0x007F0000 /* TDCV Value */
 #define XCAN_SR_TXFLL_MASK		0x00000400 /* TX FIFO is full */
 #define XCAN_SR_ESTAT_MASK		0x00000180 /* Error status */
 #define XCAN_SR_ERRWRN_MASK		0x00000040 /* Error warning */
@@ -132,6 +133,8 @@ enum xcan_reg {
 #define XCAN_DLCR_BRS_MASK		0x04000000 /* BRS Mask in DLC */
 
 /* CAN register bit shift - XCAN_<REG>_<BIT>_SHIFT */
+#define XCAN_BRPR_TDCO_SHIFT		8  /* Transmitter Delay Compensation Offset */
+#define XCAN_BRPR_TDC_ENABLE		BIT(16) /* Transmitter Delay Compensation (TDC) Enable */
 #define XCAN_BTR_SJW_SHIFT		7  /* Synchronous jump width */
 #define XCAN_BTR_TS2_SHIFT		4  /* Time segment 2 */
 #define XCAN_BTR_SJW_SHIFT_CANFD	16 /* Synchronous jump width */
@@ -140,6 +143,7 @@ enum xcan_reg {
 #define XCAN_IDR_ID2_SHIFT		1  /* Extended Message Identifier */
 #define XCAN_DLCR_DLC_SHIFT		28 /* Data length code */
 #define XCAN_ESR_REC_SHIFT		8  /* Rx Error Count */
+#define XCAN_SR_TDCV_SHIFT		16 /* TDCV Value */
 
 /* CAN frame length constants */
 #define XCAN_FRAME_MAX_DATA_LEN		8
@@ -276,6 +280,16 @@ static const struct can_bittiming_const xcan_data_bittiming_const_canfd2 = {
 	.brp_inc = 1,
 };
 
+/* Transmission Delay Compensation constants for CANFD2.0 and Versal  */
+static const struct can_tdc_const xcan_tdc_const = {
+	.tdcv_min = 0,
+	.tdcv_max = 0, /* Manual mode not supported. */
+	.tdco_min = 0,
+	.tdco_max = 64,
+	.tdcf_min = 0, /* Filter window not supported */
+	.tdcf_max = 0,
+};
+
 /**
  * xcan_write_reg_le - Write a value to the device register little endian
  * @priv:	Driver private data structure
@@ -424,6 +438,11 @@ static int xcan_set_bittiming(struct net_device *ndev)
 	    priv->devtype.cantype == XAXI_CANFD_2_0) {
 		/* Setting Baud Rate prescalar value in F_BRPR Register */
 		btr0 = dbt->brp - 1;
+		if (can_tdc_is_enabled(&priv->can)) {
+			btr0 = btr0 |
+			priv->can.tdc.tdco << XCAN_BRPR_TDCO_SHIFT |
+			XCAN_BRPR_TDC_ENABLE;
+		}
 
 		/* Setting Time Segment 1 in BTR Register */
 		btr1 = dbt->prop_seg + dbt->phase_seg1 - 1;
@@ -1483,6 +1502,23 @@ static int xcan_get_berr_counter(const struct net_device *ndev,
 	return 0;
 }
 
+/**
+ * xcan_get_auto_tdcv - Get Transmitter Delay Compensation Value
+ * @ndev:	Pointer to net_device structure
+ * @tdcv:	Pointer to TDCV value
+ *
+ * Return: 0 on success
+ */
+static int xcan_get_auto_tdcv(const struct net_device *ndev, u32 *tdcv)
+{
+	struct xcan_priv *priv = netdev_priv(ndev);
+
+	*tdcv = (priv->read_reg(priv, XCAN_SR_OFFSET) & XCAN_SR_TDCV_MASK) >>
+		 XCAN_SR_TDCV_SHIFT;
+
+	return 0;
+}
+
 static const struct net_device_ops xcan_netdev_ops = {
 	.ndo_open	= xcan_open,
 	.ndo_stop	= xcan_close,
@@ -1734,18 +1770,22 @@ static int xcan_probe(struct platform_device *pdev)
 	priv->can.do_get_berr_counter = xcan_get_berr_counter;
 	priv->can.ctrlmode_supported = CAN_CTRLMODE_LOOPBACK |
 					CAN_CTRLMODE_BERR_REPORTING;
+	priv->can.do_get_auto_tdcv = xcan_get_auto_tdcv;
 
 	if (devtype->cantype == XAXI_CANFD)
 		priv->can.data_bittiming_const =
 			&xcan_data_bittiming_const_canfd;
 
-	if (devtype->cantype == XAXI_CANFD_2_0)
+	if (devtype->cantype == XAXI_CANFD_2_0) {
 		priv->can.data_bittiming_const =
 			&xcan_data_bittiming_const_canfd2;
+		priv->can.tdc_const = &xcan_tdc_const;
+	}
 
 	if (devtype->cantype == XAXI_CANFD ||
 	    devtype->cantype == XAXI_CANFD_2_0)
-		priv->can.ctrlmode_supported |= CAN_CTRLMODE_FD;
+		priv->can.ctrlmode_supported |= CAN_CTRLMODE_FD |
+						CAN_CTRLMODE_TDC_AUTO;
 
 	priv->reg_base = addr;
 	priv->tx_max = tx_max;
-- 
2.25.1