From mboxrd@z Thu Jan 1 00:00:00 1970 From: Henrik Bork Steffensen Subject: Re: at91_can.c: Data transmission stops Date: Wed, 28 Nov 2012 16:17:59 +0100 Message-ID: <50B62B27.8020902@rosetechnology.dk> References: <50B37C90.3040904@rosetechnology.dk> <50B389D6.4050308@grandegger.com> <50B398E6.2070101@rosetechnology.dk> <50B4CA2D.5080309@rosetechnology.dk> <50B4EAE1.6070400@grandegger.com> <50B61E1B.8040904@rosetechnology.dk> <50B621DF.3050505@grandegger.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from dmz4.rosetechnology.dk ([95.154.61.7]:47515 "EHLO dmz4.rosetechnology.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932219Ab2K1PSA (ORCPT ); Wed, 28 Nov 2012 10:18:00 -0500 In-Reply-To: <50B621DF.3050505@grandegger.com> Sender: linux-can-owner@vger.kernel.org List-ID: To: Wolfgang Grandegger Cc: linux-can@vger.kernel.org On 11/28/2012 03:38 PM, Wolfgang Grandegger wrote: > On 11/28/2012 03:22 PM, Henrik Bork Steffensen wrote: >> On 11/27/2012 05:31 PM, Wolfgang Grandegger wrote: >>> On 11/27/2012 03:11 PM, Henrik Bork Steffensen wrote: >>> Hm, could you show your diffs. >> Do You mean a diff on these 7 lines, or a diff to the original file? >> >>>> I this case "at91_poll" is basicly the same as "c_can_poll", in both >>>> cases they call the function with the spinlock in the rx chain. >>> You don't need to protect against RX. Sorry, forgot that. On the c_can >>> this is necessary due to concurrent accesses to the same message RAM. >> Ok, I think that at91_can.c might have an issue in register access. >> I am not sure, but I will look into it. >> >>>> Looking at the patch Wolfgang sugested, I became uncertain of what this >>>> patch actually wants to protect. >>>> Is it the registers in the cpu can interface? (mailboxes and control >>>> regs, i don't know the hw) >>> As mentioned above, on the c_can there is definitely a race with the >>> message ram due to the busy wait after accessing it. See: >>> >>> http://lxr.linux.no/#linux+v3.6.8/drivers/net/can/c_can/c_can.c#L237 >>> >>>> Or is it the potential race between "c_can_start_xmit" and >>>> "c_can_do_tx" ? >>>> Or even the access to the net api? >>>> >>>> Would someone care to explain? >>> I will try. In at91_start_xmit, if we get interrupted >>> >>> if (!(at91_read(priv, AT91_MSR(get_tx_next_mb(priv)))& >>> AT91_MSR_MRDY) || >>> (priv->tx_next& get_next_mask(priv)) == 0) >>> >>> /* HERE */ >>> >>> netif_stop_queue(dev); >>> >>> and then at91_irq_tx() is called executing netif_wake_queue() we may end >>> up with a stopped tx queue. But I'm not yet 100% sure. >> Ok, thanks a lot. >> >> In my case i changed the driver to only use one mailbox for transmission. >> Which means that the "net_stop_queue" will be called every time a packet >> is tx'ed. >> And the "net_wake_queue" will be called after the packet is actually >> transmitted. >> >> This is as far as i can see this is 100% safe, provided that no further >> "ndo_start_xmit" >> calls come before the wake_queue call. > Yes, then the race should be gone. Anyway, we don't want that solution. We will probably move back to a number of TX mailboxes after resolving the lockup. >> Anyway, after removing the spin_lock from rx, it loads fine and seems to >> work. > It would help use to know if a spin-lock protecting the whole > at91_start_xmit() and at91_start_xmit() functions does *really* fix your > "tx-does-not-work-any-more" problem. Then we are rather sure that there > is a race. I will get back with a status. I think we need at week for the test. > >> I will do a test with the suggested changes to the tx chain and get to >> the list >> if anything interesting appears. > Not sure what changes you have in mind? Just the ones You suggested :-) Anyway, I attached this small patch to my reply to Marc a few minutes ago. Best regards, Henrik