On 1/23/26 15:25, Marc Kleine-Budde wrote:

On 22.01.2026 13:10:36, Arun Muthusamy wrote:

quoted

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 <redacted>
---
  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?

grcan_numbds() calculates the number of buffer descriptors needed based on the data length.
The condition "len <= GRCAN_CLASSIC_DATA_SIZE" addresses cases where the data length fits within a one buffer descriptor.
For data lengths greater than "GRCAN_CLASSIC_DATA_SIZE", it computes additional descriptors needed.


-- BR, Arun Muthusamy Software Engineer Frontgrade Gaisler T : +46 (0) 
700 558 528 arun.muthusamy@gaisler.com Frontgrade Gaisler AB, Kungsgatan 
12, SE-411 19 GÖTEBORG, Sweden. +46 (0) 31 775 8650, www.gaisler.com 
<http://www.gaisler.com>