linux-kernel - Re: [PATCH v3 13/15] can: grcan: Add CANFD TX support alongside legacy CAN

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Message-ID: <20260123-berserk-crocodile-of-champagne-49d2b0-mkl@pengutronix.de>
Date: Fri, 23 Jan 2026 15:25:22 +0100
From: Marc Kleine-Budde <mkl@...gutronix.de>
To: Arun Muthusamy <arun.muthusamy@...sler.com>
Cc: robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org, 
	mailhol@...nel.org, devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-can@...r.kernel.org
Subject: Re: [PATCH v3 13/15] can: grcan: Add CANFD TX support alongside
 legacy CAN

On 22.01.2026 13:10:36, Arun Muthusamy wrote:
> Include CANFD TX support with the legacy CAN support, enabling
> support for extended data payloads to provide higher bit rates.
>
> Signed-off-by: Arun Muthusamy <arun.muthusamy@...sler.com>
> ---
>  drivers/net/can/grcan.c | 102 +++++++++++++++++++++++++++++-----------
>  1 file changed, 74 insertions(+), 28 deletions(-)
>
> diff --git a/drivers/net/can/grcan.c b/drivers/net/can/grcan.c
> index 9fc18064fab1..508ad5320cff 100644
> --- a/drivers/net/can/grcan.c
> +++ b/drivers/net/can/grcan.c
> @@ -174,6 +174,7 @@ struct grcan_registers {
>  #define GRCAN_IRQ_DEFAULT (GRCAN_IRQ_RX | GRCAN_IRQ_TX | GRCAN_IRQ_ERRORS)
>
>  #define GRCAN_MSG_SIZE		16
> +#define GRCAN_CLASSIC_DATA_SIZE 8
>
>  #define GRCAN_MSG_IDE		0x80000000
>  #define GRCAN_MSG_RTR		0x40000000
> @@ -195,6 +196,10 @@ struct grcan_registers {
>  #define GRCAN_MSG_OFF		0x00000002
>  #define GRCAN_MSG_PASS		0x00000001
>
> +#define GRCAN_MSG_EID_MASK      GENMASK(28, 0)
> +#define GRCAN_MSG_BID_MASK      GENMASK(28, 18)
> +#define GRCAN_MSG_DLC_MASK      GENMASK(31, 28)
> +
>  #define GRCAN_BUFFER_ALIGNMENT		1024
>  #define GRCAN_DEFAULT_BUFFER_SIZE	1024
>  #define GRCAN_VALID_TR_SIZE_MASK	0x001fffc0
> @@ -227,6 +232,9 @@ struct grcan_registers {
>  #define GRCANFD_FDBTR_PS2_BIT 5
>  #define GRCANFD_FDBTR_SJW_BIT 0
>
> +#define GRCAN_TX_BRS  BIT(25)
> +#define GRCAN_TX_FDF  BIT(26)
> +
>  /* Hardware capabilities */
>  struct grcan_hwcap {
>  	/* CAN-FD capable, indicates GRCANFD IP.
> @@ -1218,6 +1226,13 @@ static void grcan_transmit_catch_up(struct net_device *dev)
>  	spin_unlock_irqrestore(&priv->lock, flags);
>  }
>
> +static int grcan_numbds(int len)
> +{
> +	if (len <= GRCAN_CLASSIC_DATA_SIZE)
> +		return 1;
> +	return 1 + ((len - GRCAN_CLASSIC_DATA_SIZE + GRCAN_MSG_SIZE) / GRCAN_MSG_SIZE);

This looks strange, what is calculated here? Why is "<=
GRCAN_CLASSIC_DATA_SIZE" a special case?

> +}
> +
>  static int grcan_receive(struct net_device *dev, int budget)
>  {
>  	struct grcan_priv *priv = netdev_priv(dev);
> @@ -1400,15 +1415,22 @@ static netdev_tx_t grcan_start_xmit(struct sk_buff *skb,
>  				    struct net_device *dev)
>  {
>  	struct grcan_priv *priv = netdev_priv(dev);
> -	struct grcan_registers __iomem *regs = priv->regs;
> +	struct grcan_registers __iomem *regs;
> +	u32 eff, rtr, dlc, tmp, err, can_id;
>  	struct grcan_dma *dma = &priv->dma;
> -	struct can_frame *cf = (struct can_frame *)skb->data;
> +	u32 bds, copy_len, payload_offset;
>  	u32 id, txwr, txrd, space, txctrl;
> -	int slotindex;
> -	u32 *slot;
> -	u32 rtr, eff, dlc, tmp, err;
> +	struct canfd_frame *cfd;
> +	struct can_frame *cf;
>  	unsigned long flags;
> -	u32 oneshotmode = priv->can.ctrlmode & CAN_CTRLMODE_ONE_SHOT;
> +	u32 oneshotmode;
> +	u8 *payload;
> +	u32 *slot;
> +	u8 len;
> +	int i;
> +
> +	regs = priv->regs;
> +	oneshotmode = priv->can.ctrlmode & CAN_CTRLMODE_ONE_SHOT;
>
>  	if (can_dev_dropped_skb(dev, skb))
>  		return NETDEV_TX_OK;
> @@ -1419,6 +1441,18 @@ static netdev_tx_t grcan_start_xmit(struct sk_buff *skb,
>  	if (priv->can.ctrlmode & CAN_CTRLMODE_LISTENONLY)
>  		return NETDEV_TX_BUSY;
>
> +	cfd = (struct canfd_frame *)skb->data;
> +	len     = cfd->len;
> +	can_id  = cfd->can_id;
> +	payload = cfd->data;

one space in front of the "=" please

Marc

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