Subject: Re: [PATCH] CAN: Add Flexcan CAN controller driver

From: Marc Kleine-Budde <[email-masked]>
Date: Thu, 22 Jul 2010 11:33:24 +0200

Wolfgang Grandegger wrote:
> On 07/21/2010 10:42 PM, Marc Kleine-Budde wrote:
>> Marc Kleine-Budde wrote:
>>> Wolfgang Grandegger wrote:
>>>> I realized a few issues. You can add my "acked-by" when they are fixed.
>>> thanks for the review.
>> [...]
>>
>>>>> +static void flexcan_poll_err_frame(struct net_device *dev,
>>>>> +				   struct can_frame *cf, u32 reg_esr)
>>>>> +{
>>>>> +	struct flexcan_priv *priv = netdev_priv(dev);
>>>>> +	int error_warning = 0, rx_errors = 0, tx_errors = 0;
>>>>> +
>>>>> +	if (reg_esr & FLEXCAN_ESR_BIT1_ERR) {
>>>>> +		rx_errors = 1;
>>>>> +		cf->can_id |= CAN_ERR_PROT | CAN_ERR_BUSERROR;
>>>>> +		cf->data[2] |= CAN_ERR_PROT_BIT1;
>>>>> +	}
>>>>> +
>>>>> +	if (reg_esr & FLEXCAN_ESR_BIT0_ERR) {
>>>>> +		rx_errors = 1;
>>>>> +		cf->can_id |= CAN_ERR_PROT | CAN_ERR_BUSERROR;
>>>>> +		cf->data[2] |= CAN_ERR_PROT_BIT0;
>>>>> +	}
>>>>> +
>>>>> +	if (reg_esr & FLEXCAN_ESR_FRM_ERR) {
>>>>> +		rx_errors = 1;
>>>>> +		cf->can_id |= CAN_ERR_PROT | CAN_ERR_BUSERROR;
>>>>> +		cf->data[2] |= CAN_ERR_PROT_FORM;
>>>>> +	}
>>>>> +
>>>>> +	if (reg_esr & FLEXCAN_ESR_STF_ERR) {
>>>>> +		rx_errors = 1;
>>>>> +		cf->can_id |= CAN_ERR_PROT | CAN_ERR_BUSERROR;
>>>>> +		cf->data[2] |= CAN_ERR_PROT_STUFF;
>>>>> +	}
>>>>> +
>>>>> +
>>>>> +	if (reg_esr & FLEXCAN_ESR_ACK_ERR) {
>>>>> +		tx_errors = 1;
>>>>> +		cf->can_id |= CAN_ERR_ACK;
>>>> This is a bus-error as well. Therefore I think it should be:
>>>>
>>>> 	if (reg_esr & FLEXCAN_ESR_ACK_ERR) {
>>>> 		tx_errors = 1;
>>>> 		cf->can_id |= CAN_ERR_ACK;
>>>> 		cf->can_id |= CAN_ERR_PROT | CAN_ERR_BUSERROR;
>>>> 		cf->data[3] |= CAN_ERR_PROT_LOC_ACK; /* ACK slot */
>>>> 	}
>>>>
>>>> I need to check what CAN_ERR_ACK is intended for. Then, cf->can_id could
>>>> be preset with "CAN_ERR_PROT | CAN_ERR_BUSERROR" at the beginning.
>> This controller issues an ACK error if there are no other nodes on the
>> CAN bus to send a ACK that the message has been received. Or all
>> remaining Nodes are in bus off state.
> 
> Mainly this bus error can cause the infamous IRQ and message flooding
> when no cable is connected.

No cable connected can (if your node doesn't have an activated on baord
termination) result in no termination at all, and this may result in a
different error.

At least it does on the at91. I haven't checked with the flexcan.

The subtile difference is that the CAN controller isn't allowed to go
into bus-off with a proper terminated bus when it recevies no ACKs, but
going to bus off on a not terminated bus is okay.

>> From the datasheet:
>> "This bit indicates that an acknowledge (ACK) error has been detected by
>> the transmitter node; that is, a dominant bit has not been detected
>> during the ACK SLOT."
> 
> That's what the above error describes, like on the SJA1000, apart from
> setting CAN_ERR_ACK. Setting CAN_ERR_ACK is somehow bogus, but just
> leave it for the time being. I will fix it globally when time permits.

Now I'm confused. What's the meaning of CAN_ERR_ACK? When should it be used?

Cheers, Marc

-- 
Pengutronix e.K.                  | Marc Kleine-Budde           |
Industrial Linux Solutions        | Phone: +49-231-2826-924     |
Vertretung West/Dortmund          | Fax:   +49-5121-206917-5555 |
Amtsgericht Hildesheim, HRA 2686  | http://www.pengutronix.de   |

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