netdev - Re: [PATCH net-next-2.6 v5 1/1] can: c_can: Added support for Bosch C

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Date:	Tue, 8 Feb 2011 17:04:41 +0800
From:	Bhupesh SHARMA <bhupesh.sharma@...com>
To:	'Wolfgang Grandegger' <wg@...ndegger.com>
Cc:	"socketcan-core@...ts.berlios.de" <socketcan-core@...ts.berlios.de>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Marc Kleine-Budde <mkl@...gutronix.de>
Subject: Re: [PATCH net-next-2.6 v5 1/1] can: c_can: Added support for Bosch
 C_CAN controller

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?

Regards,
Bhupesh
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