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

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Date:   Thu, 30 Mar 2023 14:46:16 +0800
From:   Peter Hong <peter_hong@...tek.com.tw>
To:     Vincent MAILHOL <mailhol.vincent@...adoo.fr>
CC:     <wg@...ndegger.com>, <mkl@...gutronix.de>,
        <michal.swiatkowski@...ux.intel.com>,
        <Steen.Hegelund@...rochip.com>, <davem@...emloft.net>,
        <edumazet@...gle.com>, <kuba@...nel.org>, <pabeni@...hat.com>,
        <frank.jungclaus@....eu>, <linux-kernel@...r.kernel.org>,
        <linux-can@...r.kernel.org>, <netdev@...r.kernel.org>,
        <hpeter+linux_kernel@...il.com>
Subject: Re: [PATCH V3] can: usb: f81604: add Fintek F81604 support

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