Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755144Ab3HLE0Q (ORCPT ); Mon, 12 Aug 2013 00:26:16 -0400 Received: from arroyo.ext.ti.com ([192.94.94.40]:43334 "EHLO arroyo.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751914Ab3HLE0L (ORCPT ); Mon, 12 Aug 2013 00:26:11 -0400 Message-ID: <5208639F.8070406@ti.com> Date: Mon, 12 Aug 2013 09:55:03 +0530 From: Sekhar Nori User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:17.0) Gecko/20130620 Thunderbird/17.0.7 MIME-Version: 1.0 To: Joel Fernandes CC: Mark Brown , Tony Lindgren , Grant Likely , Sricharan R , Russell King , Vinod Koul , Lokesh Vutla , Chris Ball , Arnd Bergmann , Rajendra Nayak , Rob Herring , Jason Kridner , Linux OMAP List , Linux ARM Kernel List , Linux DaVinci Kernel List , Balaji TK , Linux MMC List , Linux Kernel Mailing List , Santosh Shilimkar , Dan Williams , Olof Johansson , Benoit Cousson Subject: Re: [PATCH v3 02/12] ARM: edma: Don't clear EMR of channel in edma_stop References: <1375719297-12871-1-git-send-email-joelf@ti.com> <1375719297-12871-3-git-send-email-joelf@ti.com> <520385D3.1060408@ti.com> In-Reply-To: <520385D3.1060408@ti.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2401 Lines: 60 On 8/8/2013 5:19 PM, Sekhar Nori wrote: > On Monday 05 August 2013 09:44 PM, Joel Fernandes wrote: >> We certainly don't want error conditions to be cleared any other >> place but the EDMA error handler, as this will make us 'forget' >> about missed events we might need to know errors have occurred. >> >> This fixes a race condition where the EMR was being cleared >> by the transfer completion interrupt handler. >> >> Basically, what was happening was: >> >> Missed event >> | >> | >> V >> SG1-SG2-SG3-Null >> \ >> \__TC Interrupt (Almost same time as ARM is executing >> TC interrupt handler, an event got missed and also forgotten >> by clearing the EMR). >> >> This causes the following problems: >> >> 1. >> If error interrupt is also pending and TC interrupt clears the EMR >> by calling edma_stop as has been observed in the edma_callback function, >> the ARM will execute the error interrupt even though the EMR is clear. >> As a result, the dma_ccerr_handler returns IRQ_NONE. If this happens >> enough number of times, IRQ subsystem disables the interrupt thinking >> its spurious which makes error handler never execute again. >> >> 2. >> Also even if error handler doesn't return IRQ_NONE, the removing of EMR >> removes the knowledge about which channel had a missed event, and thus >> a manual trigger on such channels cannot be performed. >> >> The EMR is ultimately being cleared by the Error interrupt handler >> once it is handled so we remove code that does it in edma_stop and >> allow it to happen there. >> >> Signed-off-by: Joel Fernandes > > Queuing this for v3.11 fixes. While committing, I changed the headline > to remove capitalization and made it more readable by removing register > level details. The new headline is: > > ARM: edma: don't clear missed events in edma_stop() Forgot to ask, should this be tagged for stable? IOW, how serious is this race in current kernel (without the entire series applied)? I have never observed it myself - so please provide details how easy/difficult it is to hit this condition. Thanks, Sekhar -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/