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

[Arun Muthusamy]

On 1/27/26 15:12, Marc Kleine-Budde wrote:
> On 27.01.2026 15:06:55, Arun Muthusamy wrote:
> > On 1/23/26 15:25, Marc Kleine-Budde wrote:
> > > 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@xxxxxxxxxxx>
> > > > ---
> > > >    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.
> What happens if "len = GRCAN_CLASSIC_DATA_SIZE + GRCAN_MSG_SIZE"?
>
> | return 1 + ((len - GRCAN_CLASSIC_DATA_SIZE + GRCAN_MSG_SIZE) / GRCAN_MSG_SIZE);
>
> = 1 + ((GRCAN_CLASSIC_DATA_SIZE + GRCAN_MSG_SIZE - GRCAN_CLASSIC_DATA_SIZE + GRCAN_MSG_SIZE) / GRCAN_MSG_SIZE);
> = 1 + ((                          GRCAN_MSG_SIZE -                         + GRCAN_MSG_SIZE) / GRCAN_MSG_SIZE);
> = 1 + 2;
> = 3
>
> Is this correct?
Thanks for pointing out.
That's not correct. It will be addressed in the next patch series.

--
--
BR,

Arun Muthusamy
Software Engineer
Frontgrade Gaisler
T : +46 (0) 700 558 528
arun.muthusamy@xxxxxxxxxxx

Frontgrade Gaisler AB, Kungsgatan 12, SE-411 19 GÖTEBORG, Sweden.
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