Re: peak_pci: TX Frame Loss

[Andri Yngvason <andri.yngvason@marel.com>]

On Tue, Dec 22, 2015 at 09:13:25AM +0100, Stephane Grosjean wrote:
> Hi Andri,
> 
> We're currently investigating hard onto this issue. On my side, I'm checking
> the software part and I'd like to discuss with you about one point:
> 
> AFAIK the "sja1000_start_xmit()" function calls are really serialized by the
> network core. So there's actually no need of any lock to share the access of
> the SJA1000 registers, regarding the Tx path. Right. But I don't see in this
> function any test condition over the Transmit Status bit before writing the
> outgoing CAN frame (aka "reg[SJA1000_SR] & SR_TS").
>
I tried adding it and it didn't do anything. See original message.
> 
> Without testing the Transmit Status bit before writing, wouldn't it be
> possible that any 2nd task overwrite a 1st frame written by a 1st task
> before it has been really sent by the SJA1000?
> 
I don't think so. The _start_xmit() call is scheduled via the wait queue, so
_start_xmit() being called concurrently would be a sign of a misbehaving wait
queue, but like I said, adding the check did not yield any results.

Thanks & Merry Xmas!
Andri