[PATCH V3 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
CANFD controllers, will compensate for the measure loop delay in
the receive path.

Signed-off-by: Srinivas Neeli <srinivas.neeli at xilinx.com>
---
Changes in V3:
-Implemented GENMASK,FIELD_PERP & FIELD_GET Calls.
-Implemented TDC feature for all Xilinx CANFD controllers.
-corrected prescalar to prescaler(typo).
Changes in V2:
-Created two patchs one for revert another for TDC support.
---
 drivers/net/can/xilinx_can.c | 48 ++++++++++++++++++++++++++++++++----
 1 file changed, 43 insertions(+), 5 deletions(-)

diff --git a/drivers/net/can/xilinx_can.c b/drivers/net/can/xilinx_can.c
index e179d311aa28..288be69c0aed 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
  *
@@ -9,6 +9,7 @@
  * This driver is developed for Axi CAN IP and for Zynq CANPS Controller.
  */
 
+#include <linux/bitfield.h>
 #include <linux/clk.h>
 #include <linux/errno.h>
 #include <linux/init.h>
@@ -99,6 +100,7 @@ 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		GENMASK(22, 16) /* 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 +134,8 @@ 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		GENMASK(13, 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 */
@@ -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
@@ -405,7 +419,7 @@ static int xcan_set_bittiming(struct net_device *ndev)
 		return -EPERM;
 	}
 
-	/* Setting Baud Rate prescalar value in BRPR Register */
+	/* Setting Baud Rate prescaler value in BRPR Register */
 	btr0 = (bt->brp - 1);
 
 	/* Setting Time Segment 1 in BTR Register */
@@ -422,8 +436,12 @@ static int xcan_set_bittiming(struct net_device *ndev)
 
 	if (priv->devtype.cantype == XAXI_CANFD ||
 	    priv->devtype.cantype == XAXI_CANFD_2_0) {
-		/* Setting Baud Rate prescalar value in F_BRPR Register */
+		/* Setting Baud Rate prescaler value in F_BRPR Register */
 		btr0 = dbt->brp - 1;
+		if (can_tdc_is_enabled(&priv->can))
+			btr0 |=
+			FIELD_PREP(XCAN_BRPR_TDCO_SHIFT, priv->can.tdc.tdco) |
+			XCAN_BRPR_TDC_ENABLE;
 
 		/* Setting Time Segment 1 in BTR Register */
 		btr1 = dbt->prop_seg + dbt->phase_seg1 - 1;
@@ -1483,6 +1501,22 @@ 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 = FIELD_GET(XCAN_SR_TDCV_MASK, priv->read_reg(priv, XCAN_SR_OFFSET));
+
+	return 0;
+}
+
 static const struct net_device_ops xcan_netdev_ops = {
 	.ndo_open	= xcan_open,
 	.ndo_stop	= xcan_close,
@@ -1744,8 +1778,12 @@ static int xcan_probe(struct platform_device *pdev)
 			&xcan_data_bittiming_const_canfd2;
 
 	if (devtype->cantype == XAXI_CANFD ||
-	    devtype->cantype == XAXI_CANFD_2_0)
-		priv->can.ctrlmode_supported |= CAN_CTRLMODE_FD;
+	    devtype->cantype == XAXI_CANFD_2_0) {
+		priv->can.ctrlmode_supported |= CAN_CTRLMODE_FD |
+						CAN_CTRLMODE_TDC_AUTO;
+		priv->can.do_get_auto_tdcv = xcan_get_auto_tdcv;
+		priv->can.tdc_const = &xcan_tdc_const;
+	}
 
 	priv->reg_base = addr;
 	priv->tx_max = tx_max;
-- 
2.25.1