Re: [PATCH 2/2] can: flexcan: add support for ISO CAN-FD

[Oliver Hartkopp <socketcan@xxxxxxxxxxxx>]

On 30.06.20 07:53, Michael Walle wrote:
> [+ Oliver]
>
> Hi Joakim,
>
> Am 2020-06-30 04:42, schrieb Joakim Zhang:
> > > -----Original Message-----
> > > From: Michael Walle <michael@xxxxxxxx>
> > > Sent: 2020年6月30日 2:18
> > > To: linux-can@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx;
> > > linux-kernel@xxxxxxxxxxxxxxx
> > > Cc: Wolfgang Grandegger <wg@xxxxxxxxxxxxxx>; Marc Kleine-Budde
> > > <mkl@xxxxxxxxxxxxxx>; David S . Miller <davem@xxxxxxxxxxxxx>; Jakub
> > > Kicinski <kuba@xxxxxxxxxx>; Joakim Zhang <qiangqing.zhang@xxxxxxx>;
> > > dl-linux-imx <linux-imx@xxxxxxx>; Michael Walle <michael@xxxxxxxx>
> > > Subject: [PATCH 2/2] can: flexcan: add support for ISO CAN-FD
> > >
> > > Up until now, the controller used non-ISO CAN-FD mode, although it 
> > > supports it.
> > > Add support for ISO mode, too. By default the hardware is in non-ISO 
> > > mode and
> > > an enable bit has to be explicitly set.
> > >
> > > Signed-off-by: Michael Walle <michael@xxxxxxxx>
> > > ---
> > >  drivers/net/can/flexcan.c | 19 ++++++++++++++++---
> > >  1 file changed, 16 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/net/can/flexcan.c b/drivers/net/can/flexcan.c index
> > > 183e094f8d66..a92d3cdf4195 100644
> > > --- a/drivers/net/can/flexcan.c
> > > +++ b/drivers/net/can/flexcan.c
> > > @@ -94,6 +94,7 @@
> > >  #define FLEXCAN_CTRL2_MRP        BIT(18)
> > >  #define FLEXCAN_CTRL2_RRS        BIT(17)
> > >  #define FLEXCAN_CTRL2_EACEN        BIT(16)
> > > +#define FLEXCAN_CTRL2_ISOCANFDEN    BIT(12)
> > >
> > >  /* FLEXCAN memory error control register (MECR) bits */
> > >  #define FLEXCAN_MECR_ECRWRDIS        BIT(31)
> > > @@ -1344,14 +1345,25 @@ static int flexcan_chip_start(struct net_device
> > > *dev)
> > >      else
> > >          reg_mcr |= FLEXCAN_MCR_SRX_DIS;
> > >
> > > -    /* MCR - CAN-FD */
> > > -    if (priv->can.ctrlmode & CAN_CTRLMODE_FD)
> > > +    /* MCR, CTRL2
> > > +     *
> > > +     * CAN-FD mode
> > > +     * ISO CAN-FD mode
> > > +     */
> > > +    reg_ctrl2 = priv->read(&regs->ctrl2);
> > > +    if (priv->can.ctrlmode & CAN_CTRLMODE_FD) {
> > >          reg_mcr |= FLEXCAN_MCR_FDEN;
> > > -    else
> > > +        reg_ctrl2 |= FLEXCAN_CTRL2_ISOCANFDEN;
> > > +    } else {
> > >          reg_mcr &= ~FLEXCAN_MCR_FDEN;
> > > +    }
> > > +
> > > +    if (priv->can.ctrlmode & CAN_CTRLMODE_FD_NON_ISO)
> > > +        reg_ctrl2 &= ~FLEXCAN_CTRL2_ISOCANFDEN;
>
> [..]
> > ip link set can0 up type can bitrate 1000000 dbitrate 5000000 fd on
> > ip link set can0 up type can bitrate 1000000 dbitrate 5000000 fd on \
> >    fd-non-iso on
>
> vs.
>
> > ip link set can0 up type can bitrate 1000000 dbitrate 5000000 
> > fd-non-iso on
>
> I haven't found anything if CAN_CTRLMODE_FD_NON_ISO depends on
> CAN_CTRLMODE_FD. I.e. wether CAN_CTRLMODE_FD_NON_ISO can only be set if
> CAN_CTRLMODE_FD is also set.
>
> Only the following piece of code, which might be a hint that you
> have to set CAN_CTRLMODE_FD if you wan't to use CAN_CTRLMODE_FD_NON_ISO:
>
> drivers/net/can/dev.c:
>    /* do not check for static fd-non-iso if 'fd' is disabled */
>    if (!(maskedflags & CAN_CTRLMODE_FD))
>            ctrlstatic &= ~CAN_CTRLMODE_FD_NON_ISO;
>
> If CAN_CTRLMODE_FD_NON_ISO can be set without CAN_CTRLMODE_FD, what
> should be the mode if both are set at the same time?

CAN_CTRLMODE_FD_NON_ISO is only relevant when CAN_CTRLMODE_FD is set.

So in the example from above

ip link set can0 up type can bitrate 1000000 dbitrate 5000000 fd-non-iso on

either the setting of 'dbitrate 5000000' and 'fd-non-iso on' is pointless.

When switching to FD-mode with 'fd on' the FD relevant settings need to 
be applied.

FD ISO is the default.

Did this help or did I get anything wrong?

Best,
Oliver