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

[Marc Kleine-Budde]

Hello Srinivas Neeli,

thanks for your patch!

On 07.06.2022 14:26:54, Srinivas Neeli wrote:
> 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.

Wich controllers support TDC?

XAXI_CANFD doesn't have do_get_auto_tdc assigned, but
CAN_CTRLMODE_TDC_AUTO is set.

> 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 |

Make use of "|=" and properly indent.

> +			priv->can.tdc.tdco << XCAN_BRPR_TDCO_SHIFT |

Please include <linux/bitfield.h> and make use of "FIELD_PREP".

> +			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;

Please use FIELD_GET.

> +
> +	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;

I'm not sure, if it has any side effects, if you assign do_get_auto_tdc
for all controllers, even the ones that don't support it. Vincent can
probably clarify this.

>  
>  	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;

regards
Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
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