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 16:44:36 +0100 Message-ID: <50B63164.5090601@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> <50B61FE4.5090905@pengutronix.de> <50B62947.4090300@rosetechnology.dk> <50B629ED.40507@pengutronix.de> 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]:47527 "EHLO dmz4.rosetechnology.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753270Ab2K1Poi (ORCPT ); Wed, 28 Nov 2012 10:44:38 -0500 In-Reply-To: <50B629ED.40507@pengutronix.de> Sender: linux-can-owner@vger.kernel.org List-ID: To: Marc Kleine-Budde Cc: linux-can@vger.kernel.org On 11/28/2012 04:12 PM, Marc Kleine-Budde wrote: > On 11/28/2012 04:09 PM, Henrik Bork Steffensen wrote: >> On 11/28/2012 03:29 PM, Marc Kleine-Budde 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. >>> In your first mail you've written that using only one mailbox increases >>> the probability for a lockup. >>> >>>> 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. >>>> >>>> >>>> Anyway, after removing the spin_lock from rx, it loads fine and seems to >>>> work. >>>> I will do a test with the suggested changes to the tx chain and get to >>>> the list >>>> if anything interesting appears. >>>> >>>> Thank You very much for Your help so far :-) >>> Can you send me a diff of your current changes? >> Hi, >> >> Please note that i have not yet tested it for lockup. >> So far i just did a simple rx/tx test. > How many TX mailboxes are you using? According to your patch, the number > is unchanged. This patch only contains this tx spin_lock - the rest of the driver contains changes too. e.g: "at91_write(priv, AT91_IER, 1 << AT91_MB_TX_SINGLE_MB_NUM);" Only using one mailbox for TX was part of an divide-and-conquer process, but also because the data sheet errata suggested it for low bw applications. Henrik