Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752088AbdG1OGh convert rfc822-to-8bit (ORCPT ); Fri, 28 Jul 2017 10:06:37 -0400 Received: from us-smtp-delivery-107.mimecast.com ([63.128.21.107]:55853 "EHLO us-smtp-delivery-107.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751933AbdG1OGg (ORCPT ); Fri, 28 Jul 2017 10:06:36 -0400 Subject: Re: [PATCH v3] irqchip/tango: Don't use incorrect irq_mask_ack callback To: Florian Fainelli , Doug Berger CC: Mans Rullgard , Mason , Thomas Gleixner , Marc Zyngier , Jason Cooper , LKML , Linux ARM References: <20170719190734.18566-1-opendmb@gmail.com> <20170719190734.18566-3-opendmb@gmail.com> <7a51555f-8191-9ebd-1f30-7c20f6db9d3f@sigmadesigns.com> <8d29fec9-35b8-c33b-3091-3e9a51c99ed7@gmail.com> <6f0092f7-692f-4a15-1d95-40f4e59c8585@sigmadesigns.com> <3b858e14-0da1-d4aa-eb84-f136ece8c2a6@gmail.com> <48734beb-0e6b-3a8f-ebf4-b1cec63322e5@gmail.com> From: Marc Gonzalez Message-ID: Date: Fri, 28 Jul 2017 16:06:29 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Firefox/52.0 SeaMonkey/2.49.1 MIME-Version: 1.0 In-Reply-To: <48734beb-0e6b-3a8f-ebf4-b1cec63322e5@gmail.com> X-Originating-IP: [172.27.0.114] X-MC-Unique: JCyz9XmLOxCc2RCV_BDMfA-1 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3079 Lines: 75 On 27/07/2017 20:17, Florian Fainelli wrote: > On 07/26/2017 12:13 PM, Måns Rullgård wrote: > >> Florian Fainelli writes: >> >>> On 07/25/2017 06:29 AM, Måns Rullgård wrote: >>> >>>> Marc Gonzalez writes: >>>> >>>>> On 25/07/2017 15:16, Måns Rullgård wrote: >>>>> >>>>>> What happened to the patch adding the proper combined function? >>>>> >>>>> It appears you're not CCed on v2. >>>>> >>>>> https://patchwork.kernel.org/patch/9859799/ >>>>> >>>>> Doug wrote: >>>>>> Yes, you understand correctly. The irq_mask_ack method is entirely >>>>>> optional and I assume that is why this issue went undetected for so >>>>>> long; however, it is slightly more efficient to combine the functions >>>>>> (even if the ack is unnecessary) which is why I chose to do so for my >>>>>> changes to the irqchip-brcmstb-l2 driver where I first discovered this >>>>>> issue. How much value the improved efficiency has is certainly >>>>>> debatable, but interrupt handling is one area where people might care >>>>>> about such a small difference. As the irqchip-tango driver maintainer >>>>>> you are welcome to decide whether or not the irq_mask_ack method makes >>>>>> sense to you. >>>>> >>>>> My preference goes to leaving the irq_mask_ack callback undefined, >>>>> and let the irqchip framework use irq_mask and irq_ack instead. >>>> >>>> Why would you prefer the less efficient way? >>>> >>> >>> Same question here, that does not really make sense to me. >>> >>> The whole point of this patch series is to have a set of efficient and >>> bugfree (or nearly) helper functions that drivers can rely on, are you >>> saying that somehow using irq_mask_and_ack is exposing a bug in the >>> tango irqchip driver and using the separate functions does not expose >>> this bug? >> >> There is currently a bug in that the function used doesn't do what its >> name implies which can't be good. Using the separate mask and ack >> functions obviously works, but combining them saves a lock/unlock >> sequence. The correct combined function has already been written, so I >> see no reason not to use it. > > Marc/Mason, are you intending to get this patch accepted in order to > provide a quick bugfix targeting earlier kernels with the tango irqchip > driver or is this how you think the correct fix for the tango irqchip > driver is as opposed to using Doug's fix? Hello Florian, I am extremely grateful for you and Doug bringing the defect to my attention, as it was indeed causing an issue which I had not found the time to investigate. The reason I proposed an alternate patch is that 1) Doug didn't seem to mind, 2) simpler code leads to fewer bugs and less maintenance IME, and 3) I didn't see many drivers using the irq_mask_ack() callback (9 out of 86) with a few misusing it, by defining irq_mask = irq_mask_ack. As you point out, my patch might be slightly easier to backport than Doug's (TBH, I hadn't considered that aspect until you mentioned it). Has anyone ever quantified the performance improvement of mask_ack over mask + ack? Regards.