Re: CM-ITC, pch_can/c_can_pci, sendto() returning ENOBUFS

[dariobin@libero.it]

Hi Marc,

> Il 21/09/2022 09:47 Marc Kleine-Budde <mkl@pengutronix.de> ha scritto:
> 
>  
> On 21.09.2022 09:25:41, dariobin@libero.it wrote:
> > > On 9/16/22 06:14, Jacob Kroon wrote:
> > > ...> What I do know is that if I revert commit:
> > > > 
> > > > "can: c_can: cache frames to operate as a true FIFO"
> > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=387da6bc7a826cc6d532b1c0002b7c7513238d5f
> > > > 
> > > > then everything looks good. I don't get any BUG messages, and the host 
> > > > has been running overnight without problems, so it seems to have fixed 
> > > > the network interface lockup as well.
> > 
> > Here's what I think:
> > If one or more messages are cached, the controller has to transmit more frames 
> > in the unit of time when they can be transmitted (IF_COMM_TXRQST), different from
> > when the transmission occurs directly on request from the user space. In the case 
> > of cached data transmission I therefore think that the controller is more heavily
> > loaded. Can this shift the balance ?
> > 
> > > 
> > > I ran the kernel *with* the commit above, and also with the following patch:
> > > 
> > > > diff --git a/drivers/net/can/c_can/c_can_main.c b/drivers/net/can/c_can/c_can_main.c
> > > > index 52671d1ea17d..4375dc70e21f 100644
> > > > --- a/drivers/net/can/c_can/c_can_main.c
> > > > +++ b/drivers/net/can/c_can/c_can_main.c
> > > > @@ -1,3 +1,4 @@
> > > > +#define DEBUG
> > > >  /*
> > > >   * CAN bus driver for Bosch C_CAN controller
> > > >   *
> > > > @@ -469,8 +470,15 @@ static netdev_tx_t c_can_start_xmit(struct sk_buff *skb,
> > > >  	if (c_can_get_tx_free(tx_ring) == 0)
> > > >  		netif_stop_queue(dev);
> > > >  
> > > > -	if (idx < c_can_get_tx_tail(tx_ring))
> > > > +	netdev_dbg(dev, "JAKR:%d:%d:%d:%d\n", idx,
> > > > +	                                      c_can_get_tx_head(tx_ring),
> > > > +	                                      c_can_get_tx_tail(tx_ring),
> > > > +	                                      c_can_get_tx_free(tx_ring));
> > > > +
> > > > +	if (idx < c_can_get_tx_tail(tx_ring)) {
> > > >  		cmd &= ~IF_COMM_TXRQST; /* Cache the message */
> > > > +		netdev_dbg(dev, "JAKR:Caching messages\n");
> > > > +	}
> > > >  
> > > >  	/* Store the message in the interface so we can call
> > > >  	 * can_put_echo_skb(). We must do this before we enable
> > > 
> > > and I've uploaded the entire log I could capture from /dev/kmsg, right 
> > > up to the hang, here:
> > > 
> > > https://pastebin.com/6hvAcPc9
> > > 
> > > What looks odd to me right from the start is that sometimes when idx 
> > > rolls over to 0, and *only* when it rolls over to 0, the CAN frame gets 
> > > cached because "idx < c_can_get_tx_tail(tx_ring)".
> > 
> > If the message were not stored but transmitted, the order of transmission 
> > would not be respected.
> > 
> > > 
> > > Is it possible there is some difference between c_can and d_can in how 
> > > the HW buffers are working, which breaks the driver on my particular HW 
> > > setup ?
> > > 
> > 
> > I tested the patch on a beaglebone board without encountering any problems.
> > There is also a version of the driver I submitted to Xenomai running on a custom
> > board without problems. But surely the setup and context is different from yours.
> > 
> > What compatible are you using in your device tree?
> > I used "ti,am3352-d_can".
> 
> I think Jacob's board has a c_can core, while the beagle bone uses a
> d_can. Maybe there's a subtle difference between these cores?
> 
> Dario, do you have access to a real c_can core to test?
No, only d_can core.

> 
> As reverting 387da6bc7a82 ("can: c_can: cache frames to operate as a
> true FIFO") helps to fix Jacob's problem, a temporary solution might be
> to only cache frames on d_can cores.
OK

Thanks and regards,
Dario

> 
> regards,
> Marc
> 
> -- 
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