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Message-ID: <a53ed3b5-0fbb-4f44-ab1a-3bad0373068d@kernel.org>
Date: Tue, 23 Dec 2025 22:09:08 +0100
From: Vincent Mailhol <mailhol@...nel.org>
To: Arun Muthusamy <arun.muthusamy@...sler.com>, robh@...nel.org,
krzk+dt@...nel.org, conor+dt@...nel.org, mkl@...gutronix.de
Cc: devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-can@...r.kernel.org
Subject: Re: [PATCH v2 10/10] can: grcan: Add CANFD support alongside legacy
CAN
On 23/12/2025 at 11:56, Arun Muthusamy wrote:
> Include CANFD support with the legacy CAN support, enabling
> support for extended data payloads up to 64 bytes, higher bit rates,
> handle canecho frames.
The patch mixes code refactor with introduction of new feature. I am
only a partial review for now, waiting for a proper split to do the
full review.
> Signed-off-by: Arun Muthusamy <arun.muthusamy@...sler.com>
> ---
> drivers/net/can/grcan.c | 259 +++++++++++++++++++++++++++-------------
> 1 file changed, 177 insertions(+), 82 deletions(-)
>
> diff --git a/drivers/net/can/grcan.c b/drivers/net/can/grcan.c
> index bf1c503d575d..3d5b4c7e58bc 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
> @@ -230,6 +231,12 @@ 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)
> +
> +#define GRCAN_RX_BRS BIT(25)
> +#define GRCAN_RX_FDF BIT(26)
> +
> /* Hardware capabilities */
> struct grcan_hwcap {
> /* CAN-FD capable, indicates GRCANFD IP.
> @@ -290,6 +297,13 @@ struct grcan_priv {
>
> struct sk_buff **echo_skb; /* We allocate this on our own */
>
> + /*
> + * Since the CAN FD frame has a variable length, this variable is used
> + * to keep track of the index of the CAN echo skb (socket buffer) frame.
> + * It's important for ensuring that we correctly manage the echo skb.
> + */
> + u32 echo_skb_idx;
> +
> /* The echo skb pointer, pointing into echo_skb and indicating which
> * frames can be echoed back. See the "Notes on the tx cyclic buffer
> * handling"-comment for grcan_start_xmit for more details.
> @@ -570,7 +584,7 @@ static int catch_up_echo_skb(struct net_device *dev, int budget, bool echo)
> struct grcan_registers __iomem *regs = priv->regs;
> struct grcan_dma *dma = &priv->dma;
> struct net_device_stats *stats = &dev->stats;
> - int i, work_done;
> + int work_done;
>
> /* Updates to priv->eskbp and wake-ups of the queue needs to
> * be atomic towards the reads of priv->eskbp and shut-downs
> @@ -581,19 +595,22 @@ static int catch_up_echo_skb(struct net_device *dev, int budget, bool echo)
> for (work_done = 0; work_done < budget || budget < 0; work_done++) {
> if (priv->eskbp == txrd)
> break;
> - i = priv->eskbp / GRCAN_MSG_SIZE;
> - if (echo) {
> - /* Normal echo of messages */
> - stats->tx_packets++;
> - stats->tx_bytes += can_get_echo_skb(dev, i, NULL);
> - } else {
> - /* For cleanup of untransmitted messages */
> - can_free_echo_skb(dev, i, NULL);
> - }
>
> priv->eskbp = grcan_ring_add(priv->eskbp, GRCAN_MSG_SIZE,
> dma->tx.size);
> txrd = grcan_read_reg(®s->txrd);
> +
> + /* Grab the packet once the packet is send or free untransmitted packet*/
> + if (priv->eskbp == txrd) {
> + if (echo) {
> + /* Normal echo of messages */
> + stats->tx_packets++;
> + stats->tx_bytes += can_get_echo_skb(dev, priv->echo_skb_idx, NULL);
> + } else {
> + /* For cleanup of untransmitted messages */
> + can_free_echo_skb(dev, priv->echo_skb_idx, NULL);
> + }
> + }
> }
> return work_done;
> }
> @@ -676,10 +693,8 @@ static void grcan_err(struct net_device *dev, u32 sources, u32 status)
> (status & GRCAN_STAT_ERRCTR_RELATED)) {
> enum can_state state = priv->can.state;
> enum can_state oldstate = state;
> - u32 txerr = (status & GRCAN_STAT_TXERRCNT)
> - >> GRCAN_STAT_TXERRCNT_BIT;
> - u32 rxerr = (status & GRCAN_STAT_RXERRCNT)
> - >> GRCAN_STAT_RXERRCNT_BIT;
> + u32 txerr = (status & GRCAN_STAT_TXERRCNT) >> GRCAN_STAT_TXERRCNT_BIT;
> + u32 rxerr = (status & GRCAN_STAT_RXERRCNT) >> GRCAN_STAT_RXERRCNT_BIT;
Do not add random code refactors to your patch. If you want to change
those lines, put it in a separate patch.
> /* Figure out current state */
> if (status & GRCAN_STAT_OFF) {
> @@ -1101,6 +1116,7 @@ static int grcan_set_mode(struct net_device *dev, enum can_mode mode)
> if (!(priv->can.ctrlmode & CAN_CTRLMODE_LISTENONLY))
> netif_wake_queue(dev);
> }
> + priv->echo_skb_idx = 0;
> spin_unlock_irqrestore(&priv->lock, flags);
> return err;
> }
> @@ -1150,7 +1166,6 @@ static int grcan_open(struct net_device *dev)
> netif_start_queue(dev);
> priv->resetting = false;
> priv->closing = false;
> -
> spin_unlock_irqrestore(&priv->lock, flags);
>
> return 0;
> @@ -1221,20 +1236,31 @@ 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);
> +}
> +
> static int grcan_receive(struct net_device *dev, int budget)
> {
> + struct net_device_stats *stats = &dev->stats;
> struct grcan_priv *priv = netdev_priv(dev);
> - struct grcan_registers __iomem *regs = priv->regs;
> + struct grcan_registers __iomem *regs;
> struct grcan_dma *dma = &priv->dma;
> - struct net_device_stats *stats = &dev->stats;
> - struct can_frame *cf;
> + u32 bds, copy_len, payload_offset;
> + u32 wr, rd, dlc, startrd;
> + struct canfd_frame *cf;
> + int i, work_done = 0;
> struct sk_buff *skb;
> - u32 wr, rd, startrd;
> - u32 *slot;
> u32 rtr, eff;
> - int work_done = 0;
> + u32 *slot;
> + u8 *data;
>
> + regs = priv->regs;
> rd = grcan_read_reg(®s->rxrd);
> +
> startrd = rd;
> for (work_done = 0; work_done < budget; work_done++) {
> /* Check for packet to receive */
> @@ -1242,44 +1268,70 @@ static int grcan_receive(struct net_device *dev, int budget)
> if (rd == wr)
> break;
>
> - /* Take care of packet */
> - skb = alloc_can_skb(dev, &cf);
> - if (skb == NULL) {
> + slot = dma->rx.buf + rd;
> +
> + if (slot[1] & GRCAN_RX_FDF)
> + skb = alloc_canfd_skb(dev, &cf);
> + else
> + skb = alloc_can_skb(priv->dev, (struct can_frame **)&cf);
> +
> + if (unlikely(!skb)) {
> netdev_err(dev,
> "dropping frame: skb allocation failed\n");
> stats->rx_dropped++;
> continue;
> }
>
> - slot = dma->rx.buf + rd;
> - eff = slot[0] & GRCAN_MSG_IDE;
> - rtr = slot[0] & GRCAN_MSG_RTR;
> - if (eff) {
> - cf->can_id = ((slot[0] & GRCAN_MSG_EID)
> - >> GRCAN_MSG_EID_BIT);
> - cf->can_id |= CAN_EFF_FLAG;
> - } else {
> - cf->can_id = ((slot[0] & GRCAN_MSG_BID)
> - >> GRCAN_MSG_BID_BIT);
> - }
> - cf->len = can_cc_dlc2len((slot[1] & GRCAN_MSG_DLC)
> - >> GRCAN_MSG_DLC_BIT);
> - if (rtr) {
> - cf->can_id |= CAN_RTR_FLAG;
> - } else {
> - if (cf->can_dlc > 0) {
> - memcpy(cf->data, &slot[2], sizeof(u32));
> - if (cf->can_dlc > 4)
> - memcpy(cf->data + 4, &slot[3], sizeof(u32));
> + dlc = (slot[1] & GRCAN_MSG_DLC) >> GRCAN_MSG_DLC_BIT;
> + if (slot[1] & GRCAN_RX_FDF)
> + cf->len = can_fd_dlc2len(dlc);
> + else
> + cf->len = can_cc_dlc2len(dlc);
> +
> + bds = grcan_numbds(cf->len);
> + payload_offset = 0;
> + data = cf->data;
> +
> + for (i = 0; i < bds; i++) {
> + slot = dma->rx.buf + rd;
> +
> + if (i == 0) {
> + eff = slot[0] & GRCAN_MSG_IDE;
> + rtr = slot[0] & GRCAN_MSG_RTR;
> + if (eff) {
> + cf->can_id = ((slot[0] & GRCAN_MSG_EID)
> + >> GRCAN_MSG_EID_BIT);
Use FIELD_GET() here. Add the required GRCAN_MSG_EID_MASK macro in a
dedicated clean-up patch.
> + cf->can_id |= CAN_EFF_FLAG;
> + } else {
> + cf->can_id = ((slot[0] & GRCAN_MSG_BID)
> + >> GRCAN_MSG_BID_BIT);
> + }
> + if (rtr)
> + cf->can_id |= CAN_RTR_FLAG;
> +
> + dlc = (slot[1] & GRCAN_MSG_DLC) >> GRCAN_MSG_DLC_BIT;
Same.
> + if (slot[1] & GRCAN_RX_FDF)
> + cf->len = can_fd_dlc2len(dlc);
> + else
> + cf->len = can_cc_dlc2len(dlc);
> +
> + copy_len = min(cf->len, GRCAN_CLASSIC_DATA_SIZE);
> + memcpy(data, &slot[2], copy_len);
> + payload_offset += copy_len;
> + } else {
> + copy_len = min(cf->len - payload_offset, GRCAN_MSG_SIZE);
> + memcpy(data + payload_offset, slot, copy_len);
> + payload_offset += copy_len;
> }
> -
> - stats->rx_bytes += cf->len;
> + rd += GRCAN_MSG_SIZE;
> + if (rd >= dma->tx.size)
> + rd -= dma->tx.size;
> }
> - stats->rx_packets++;
>
> + /* Update statistics and read pointer */
> + stats->rx_packets++;
> + stats->rx_bytes += cf->len;
> netif_receive_skb(skb);
> -
> - rd = grcan_ring_add(rd, GRCAN_MSG_SIZE, dma->rx.size);
> }
>
> /* Make sure everything is read before allowing hardware to
> @@ -1404,15 +1456,22 @@ 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;
> @@ -1423,6 +1482,20 @@ static netdev_tx_t grcan_start_xmit(struct sk_buff *skb,
> if (priv->can.ctrlmode & CAN_CTRLMODE_LISTENONLY)
> return NETDEV_TX_BUSY;
>
> + if (can_is_canfd_skb(skb)) {
> + cfd = (struct canfd_frame *)skb->data;
> + len = cfd->len;
> + dlc = can_fd_len2dlc(cfd->len);
> + can_id = cfd->can_id;
> + payload = cfd->data;
> + } else {
> + cf = (struct can_frame *)skb->data;
> + len = cf->len;
> + dlc = can_get_cc_dlc(cf, priv->can.ctrlmode);
> + can_id = cf->can_id;
> + payload = cf->data;
> + }
struct canfd_frame and struct can_frame share the same layout so try
to factorize what can be factorized, that is to say, everything except
of the dlc assignment.
> /* Reads of priv->eskbp and shut-downs of the queue needs to
> * be atomic towards the updates to priv->eskbp and wake-ups
> * of the queue in the interrupt handler.
> @@ -1431,9 +1504,7 @@ static netdev_tx_t grcan_start_xmit(struct sk_buff *skb,
>
> txwr = grcan_read_reg(®s->txwr);
> space = grcan_txspace(dma->tx.size, txwr, priv->eskbp);
> -
> - slotindex = txwr / GRCAN_MSG_SIZE;
> - slot = dma->tx.buf + txwr;
> + bds = grcan_numbds(len);
>
> if (unlikely(space == 1))
> netif_stop_queue(dev);
> @@ -1449,25 +1520,38 @@ static netdev_tx_t grcan_start_xmit(struct sk_buff *skb,
> return NETDEV_TX_BUSY;
> }
>
> - /* Convert and write CAN message to DMA buffer */
> - eff = cf->can_id & CAN_EFF_FLAG;
> - rtr = cf->can_id & CAN_RTR_FLAG;
> - id = cf->can_id & (eff ? CAN_EFF_MASK : CAN_SFF_MASK);
> - dlc = cf->len;
> - if (eff)
> - tmp = (id << GRCAN_MSG_EID_BIT) & GRCAN_MSG_EID;
> - else
> - tmp = (id << GRCAN_MSG_BID_BIT) & GRCAN_MSG_BID;
> - slot[0] = (eff ? GRCAN_MSG_IDE : 0) | (rtr ? GRCAN_MSG_RTR : 0) | tmp;
> -
> - slot[1] = ((dlc << GRCAN_MSG_DLC_BIT) & GRCAN_MSG_DLC);
> - slot[2] = 0;
> - slot[3] = 0;
> - if (dlc > 0) {
> - memcpy(&slot[2], cf->data, sizeof(u32));
> - slot[2] = *(u32 *)(cf->data);
> - if (dlc > 4)
> - memcpy(&slot[3], cf->data + 4, sizeof(u32));
> + payload_offset = 0;
> + for (i = 0; i < bds; i++) {
> + slot = dma->tx.buf + txwr;
> + memset(slot, 0, GRCAN_MSG_SIZE);
> +
> + if (i == 0) {
> + eff = can_id & CAN_EFF_FLAG;
> + rtr = can_id & CAN_RTR_FLAG;
> + id = can_id & (eff ? CAN_EFF_MASK : CAN_SFF_MASK);
> + if (eff)
> + tmp = (id << GRCAN_MSG_EID_BIT) & GRCAN_MSG_EID;
> + else
> + tmp = (id << GRCAN_MSG_BID_BIT) & GRCAN_MSG_BID;
> + slot[0] = (eff ? GRCAN_MSG_IDE : 0) | (rtr ? GRCAN_MSG_RTR : 0) | tmp;
> + slot[1] = ((dlc << GRCAN_MSG_DLC_BIT) & GRCAN_MSG_DLC);
> + if (can_is_canfd_skb(skb)) {
> + slot[1] |= GRCAN_TX_FDF;
> + if (cfd->flags & CANFD_BRS)
> + slot[1] |= GRCAN_TX_BRS;
> + }
> +
> + copy_len = min(len, 8);
> + memcpy(&slot[2], payload, copy_len);
> + payload_offset += copy_len;
> + } else {
> + copy_len = min(len - payload_offset, GRCAN_MSG_SIZE);
> + memcpy(slot, payload + payload_offset, copy_len);
> + payload_offset += copy_len;
> + }
> + txwr += GRCAN_MSG_SIZE;
> + if (txwr >= dma->tx.size)
> + txwr -= dma->tx.size;
> }
>
> /* Checking that channel has not been disabled. These cases
> @@ -1502,7 +1586,14 @@ static netdev_tx_t grcan_start_xmit(struct sk_buff *skb,
> * can_put_echo_skb would be an error unless other measures are
> * taken.
> */
> - can_put_echo_skb(skb, dev, slotindex, 0);
> +
> + can_put_echo_skb(skb, dev, priv->echo_skb_idx, 0);
> +
> + /* Move to the next index in the echo skb buffer */
> + priv->echo_skb_idx = (priv->echo_skb_idx + 1) % priv->can.echo_skb_max;
> +
> + if (priv->can.echo_skb[priv->echo_skb_idx])
> + netif_stop_queue(dev);
>
> /* Make sure everything is written before allowing hardware to
> * read from the memory
> @@ -1510,8 +1601,7 @@ static netdev_tx_t grcan_start_xmit(struct sk_buff *skb,
> wmb();
>
> /* Update write pointer to start transmission */
> - grcan_write_reg(®s->txwr,
> - grcan_ring_add(txwr, GRCAN_MSG_SIZE, dma->tx.size));
> + grcan_write_reg(®s->txwr, txwr);
>
> return NETDEV_TX_OK;
> }
> @@ -1662,11 +1752,16 @@ static int grcan_setup_netdev(struct platform_device *ofdev,
> priv->ofdev_dev = &ofdev->dev;
> priv->regs = base;
> priv->can.bittiming_const = hwcap->bt_const;
> + priv->can.fd.data_bittiming_const = hwcap->bt_const;
> priv->can.do_set_mode = grcan_set_mode;
> priv->can.do_get_berr_counter = grcan_get_berr_counter;
> priv->can.clock.freq = ambafreq;
> - priv->can.ctrlmode_supported =
> - CAN_CTRLMODE_LISTENONLY | CAN_CTRLMODE_ONE_SHOT;
> + if (hwcap->fd)
> + priv->can.ctrlmode_supported = CAN_CTRLMODE_LISTENONLY |
> + CAN_CTRLMODE_ONE_SHOT | CAN_CTRLMODE_FD;
> + else
> + priv->can.ctrlmode_supported = CAN_CTRLMODE_LISTENONLY |
> + CAN_CTRLMODE_ONE_SHOT;
Do it like this:
priv->can.ctrlmode_supported =
CAN_CTRLMODE_LISTENONLY | CAN_CTRLMODE_ONE_SHOT;
if (hwcap->fd)
priv->can.ctrlmode_supported |= CAN_CTRLMODE_FD;
> priv->need_txbug_workaround = txbug;
> priv->hwcap = hwcap;
>
Yours sincerely,
Vincent Mailhol
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