Subject: Re: [PATCH net-next-2.6 v5 1/1] can: c_can: Added support for Bosch C_CAN controller

From: Wolfgang Grandegger <[email-masked]>
Date: Tue, 08 Feb 2011 11:30:38 +0100

On 02/08/2011 10:04 AM, Bhupesh SHARMA wrote:
> Hi Wolfgang,
> 
>>> + stats->rx_errors++; 
>>> + cf->can_id |= CAN_ERR_PROT | CAN_ERR_BUSERROR; 
>>> + cf->data[2] |= CAN_ERR_PROT_UNSPEC; 
>>> + 
>>> + switch (lec_type) { 
>>> + case LEC_STUFF_ERROR: 
>>> + netdev_dbg(dev, "stuff error\n"); 
>>> + cf->data[2] |= CAN_ERR_PROT_STUFF; 
>>> + break; 
>>> + 
>>> + case LEC_FORM_ERROR: 
>>> + netdev_dbg(dev, "form error\n"); 
>>> + cf->data[2] |= CAN_ERR_PROT_FORM; 
>>> + break; 
>>> + 
>>> + case LEC_ACK_ERROR: 
>>> + netdev_dbg(dev, "ack error\n"); 
>>> + cf->data[2] |= (CAN_ERR_PROT_LOC_ACK | 
>>> + CAN_ERR_PROT_LOC_ACK_DEL); 
>>> + break; 
>>> + 
>>> + case LEC_BIT1_ERROR: 
>>> + netdev_dbg(dev, "bit1 error\n"); 
>>> + cf->data[2] |= CAN_ERR_PROT_BIT1; 
>>> + break; 
>>> + 
>>> + case LEC_BIT0_ERROR: 
>>> + netdev_dbg(dev, "bit0 error\n"); 
>>> + cf->data[2] |= CAN_ERR_PROT_BIT0; 
>>> + break; 
>>> + 
>>> + case LEC_CRC_ERROR: 
>>> + netdev_dbg(dev, "CRC error\n"); 
>>> + cf->data[2] |= (CAN_ERR_PROT_LOC_CRC_SEQ | 
>>> + CAN_ERR_PROT_LOC_CRC_DEL); 
>>> + break; 
>>> + } 
> 
>>>From the C_CAN manual: 
>>
>> "The LEC field holds a code which indicates the type of the last error 
>> to occur on the CAN bus. This field will be cleared to '0' when a 
>> message has been transferred (reception or transmission) without error. 
>> The unused code '7' may be written by the CPU to check for updates." 
> 
>> Not sure if it's necessary to reset the lec at init and after an error 
>> to 0x7 and check it. More below...
> 
> I worked on your suggestion and instead found that the follow algo must be used
> for reading updated `lec` values:
> a. Init lec by 0x07 at start.
> b. In function `c_can_err` check if lec is 0x7 (no bus error since this value was
> written by CPU on status register) or 0x0 (no error). If so, return without
> sending an error frame on stack. Else, check for the lec error type and
> submit error frame on stack accordingly.
> c. In case a lec error is found and served in `c_can_err` routine, write
> lec value to 0x07 again in status reg to check for updated lec later.
> 
> This is my understanding after reading the specs time and again and
> implementing/testing the logic.
> 
> Do you think this is fine or do you have any better approach?

That's what I remember from the CC770 driver. Search for lec in:

http://svn.berlios.de/wsvn/socketcan/trunk/kernel/2.6/drivers/net/can/cc770/cc770.c

Wolfgang.