Re: [PATCH V3] can: usb: f81604: add Fintek F81604 support

[Peter Hong]

Hi Vincent,

Vincent MAILHOL 於 2023/3/28 下午 12:49 寫道:
> > > > +static int f81604_set_reset_mode(struct net_device *netdev)
> > > > +{
> > > > +       struct f81604_port_priv *priv = netdev_priv(netdev);
> > > > +       int status, i;
> > > > +       u8 tmp;
> > > > +
> > > > +       /* disable interrupts */
> > > > +       status = f81604_set_sja1000_register(priv->dev, netdev->dev_id,
> > > > +                                            SJA1000_IER, IRQ_OFF);
> > > > +       if (status)
> > > > +               return status;
> > > > +
> > > > +       for (i = 0; i < F81604_SET_DEVICE_RETRY; i++) {
> > > Thanks for removing F81604_USB_MAX_RETRY.
> > >
> > > Yet, I still would like to understand why you need one hundred tries?
> > > Is this some paranoiac safenet? Or does the device really need so many
> > > attempts to operate reliably? If those are needed, I would like to
> > > understand the root cause.
> > This section is copy from sja1000.c. In my test, the operation/reset may
> > retry 1 times.
> > I'll reduce it from 100 to 10 times.
> Is it because the device is not ready? Does this only appear at
> startup or at random?

I'm using ip link up/down to test open/close(). It's may not ready so fast.
but the maximum retry is only 1 for test 10000 times.

> > > > +static int f81604_set_termination(struct net_device *netdev, u16 term)
> > > > +{
> > > > +       struct f81604_port_priv *port_priv = netdev_priv(netdev);
> > > > +       struct f81604_priv *priv;
> > > > +       u8 mask, data = 0;
> > > > +       int r;
> > > > +
> > > > +       priv = usb_get_intfdata(port_priv->intf);
> > > > +
> > > > +       if (netdev->dev_id == 0)
> > > > +               mask = F81604_CAN0_TERM;
> > > > +       else
> > > > +               mask = F81604_CAN1_TERM;
> > > > +
> > > > +       if (term == F81604_TERMINATION_ENABLED)
> > > > +               data = mask;
> > > > +
> > > > +       mutex_lock(&priv->mutex);
> > > Did you witness a race condition?
> > >
> > > As far as I know, this call back is only called while the network
> > > stack big kernel lock (a.k.a. rtnl_lock) is being hold.
> > > If you have doubt, try adding a:
> > >
> > >     ASSERT_RTNL()
> > >
> > > If this assert works, then another mutex is not needed.
> > It had added ASSERT_RTNL() into f81604_set_termination(). It only assert
> > in f81604_probe() -> f81604_set_termination(), not called via ip command:
> >       ip link set dev can0 type can termination 120
> >       ip link set dev can0 type can termination 0
> >
> > so I'll still use mutex on here.
> Sorry, do you mean that the assert throws warnings for f81604_probe()
> -> f81604_set_termination() but that it is OK (no warning) for ip
> command?
>
> I did not see that you called f81604_set_termination() internally.
> Indeed, rtnl_lock is not held in probe(). But I think it is still OK.
> In f81604_probe() you call f81604_set_termination() before
> register_candev(). If the device is not yet registered,
> f81604_set_termination() can not yet be called via ip command. Can you
> describe more precisely where you think there is a concurrency issue?
> I still do not see it.

Sorry, I had inverse the mean of ASSERT_RTNL(). It like you said.
    f81604_probe() not held rtnl_lock.
    ip set terminator will held rtnl_lock.

Due to f81604_set_termination() will called by f81604_probe() to 
initialize, it may need mutex in
situation as following:

User is setting can0 terminator when f81604_probe() complete generate 
can0 and generating can1.
So IMO, the mutex may needed.

> > > > +               port_priv->can.do_get_berr_counter = f81604_get_berr_counter;
> > > > +               port_priv->can.ctrlmode_supported =
> > > > +                       CAN_CTRLMODE_LISTENONLY | CAN_CTRLMODE_3_SAMPLES |
> > > > +                       CAN_CTRLMODE_ONE_SHOT | CAN_CTRLMODE_BERR_REPORTING |
> > > > +                       CAN_CTRLMODE_CC_LEN8_DLC | CAN_CTRLMODE_PRESUME_ACK;
> > > Did you test the CAN_CTRLMODE_CC_LEN8_DLC feature? Did you confirm
> > > that you can send and receive DLC greater than 8?
> > Sorry, I had misunderstand the define. This device is only support 0~8
> > data length,
>    ^^^^^^^^^^^
>
> Data length or Data Length Code (DLC)? Classical CAN maximum data
> length is 8 but maximum DLC is 15 (and DLC 8 to 15 mean a data length
> of 8).

This device can't support DLC > 8. It's only support 0~8.

Thanks