linux-kernel - [PATCH] can: xilinx_can: Add Transmitter delay compensation (TDC) feature support

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Date:   Thu, 12 May 2022 19:29:01 +0530
From:   Srinivas Neeli <srinivas.neeli@...inx.com>
To:     <wg@...ndegger.com>, <mkl@...gutronix.de>, <davem@...emloft.net>,
        <edumazet@...gle.com>, <appana.durga.rao@...inx.com>,
        <sgoud@...inx.com>, <michal.simek@...inx.com>
CC:     <kuba@...nel.org>, <pabeni@...hat.com>,
        <linux-can@...r.kernel.org>, <netdev@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <git@...inx.com>,
        Srinivas Neeli <srinivas.neeli@...inx.com>
Subject: [PATCH] can: xilinx_can: Add Transmitter delay compensation (TDC) feature support

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.
TDC feature requires BRP values can be 1 or 2.
The current CAN framework does not limit the brp so while using TDC,
have to restrict BRP values.
Ex:
ip link set can0 type can tq 12 prop-seg 39 phase-seg1 20 phase-seg2 20
sjw 20 dtq 12 dprop-seg 5 dphase-seg1 6 dphase-seg2 4 dsjw 4 fd on
loopback on tdco 12 tdc-mode auto

Signed-off-by: Srinivas Neeli <srinivas.neeli@...inx.com>
---
 drivers/net/can/xilinx_can.c | 30 +++++++++++++++++++++++++-----
 1 file changed, 25 insertions(+), 5 deletions(-)

diff --git a/drivers/net/can/xilinx_can.c b/drivers/net/can/xilinx_can.c
index e2b15d29d15e..7af518fbed02 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
  *
@@ -133,6 +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_CANFD	8  /* Transmitter Delay Compensation Offset */
+#define XCAN_BRPR_TDCE_SHIFT_CANFD	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 */
@@ -259,7 +261,7 @@ static const struct can_bittiming_const xcan_bittiming_const_canfd2 = {
 	.tseg2_min = 1,
 	.tseg2_max = 128,
 	.sjw_max = 128,
-	.brp_min = 2,
+	.brp_min = 1,
 	.brp_max = 256,
 	.brp_inc = 1,
 };
@@ -272,11 +274,21 @@ static struct can_bittiming_const xcan_data_bittiming_const_canfd2 = {
 	.tseg2_min = 1,
 	.tseg2_max = 16,
 	.sjw_max = 16,
-	.brp_min = 2,
+	.brp_min = 1,
 	.brp_max = 256,
 	.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
@@ -425,6 +437,11 @@ 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_CANFD |
+			1 << XCAN_BRPR_TDCE_SHIFT_CANFD;
+		}
 
 		/* Setting Time Segment 1 in BTR Register */
 		btr1 = dbt->prop_seg + dbt->phase_seg1 - 1;
@@ -1747,13 +1764,16 @@ static int xcan_probe(struct platform_device *pdev)
 		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