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Thu, 23 Apr 2020 08:17:05 -0000 (UTC) Received: by smtp.codeaurora.org (Postfix, from userid 1001) id DF2DFC432C2; Thu, 23 Apr 2020 08:17:04 +0000 (UTC) Received: from mail.codeaurora.org (localhost.localdomain [127.0.0.1]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: saiprakash.ranjan) by smtp.codeaurora.org (Postfix) with ESMTPSA id 0A186C433D2; Thu, 23 Apr 2020 08:17:04 +0000 (UTC) MIME-Version: 1.0 Date: Thu, 23 Apr 2020 13:47:03 +0530 From: Sai Prakash Ranjan To: Doug Anderson , Will Deacon , Robin Murphy Subject: Re: [PATCH] iommu/arm-smmu: Demote error messages to debug in shutdown callback In-Reply-To: References: <20200327132852.10352-1-saiprakash.ranjan@codeaurora.org> <0023bc68-45fb-4e80-00c8-01fd0369243f@arm.com> <37db9a4d524aa4d7529ae47a8065c9e0@codeaurora.org> <5858bdac-b7f9-ac26-0c0d-c9653cef841d@arm.com> <890456524e2df548ba5d44752513a62c@codeaurora.org> <20200331074400.GB25612@willie-the-truck> <1bf04938249bcd5b2111c1921facfd25@codeaurora.org> Message-ID: <6c82e688f335b9c07b0f52987244664b@codeaurora.org> X-Sender: saiprakash.ranjan@codeaurora.org User-Agent: Roundcube Webmail/1.3.9 Cc: linux-arm-msm , linux-arm-msm-owner@vger.kernel.org, "list@263.net:IOMMU DRIVERS , Joerg Roedel , " , LKML X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" Hi, On 2020-04-23 01:19, Doug Anderson wrote: > Hi, > > On Tue, Mar 31, 2020 at 12:53 AM Sai Prakash Ranjan > wrote: >> >> Hi Will, >> >> On 2020-03-31 13:14, Will Deacon wrote: >> > On Tue, Mar 31, 2020 at 01:06:11PM +0530, Sai Prakash Ranjan wrote: >> >> On 2020-03-30 23:54, Doug Anderson wrote: >> >> > On Sat, Mar 28, 2020 at 12:35 AM Sai Prakash Ranjan >> >> > wrote: >> >> > > >> >> > > > Of course the fact that in practice we'll *always* see the warning >> >> > > > because there's no way to tear down the default DMA domains, and even >> >> > > > if all devices *have* been nicely quiesced there's no way to tell, is >> >> > > > certainly less than ideal. Like I say, it's not entirely clear-cut >> >> > > > either way... >> >> > > > >> >> > > >> >> > > Thanks for these examples, good to know these scenarios in case we >> >> > > come >> >> > > across these. >> >> > > However, if we see these error/warning messages appear everytime then >> >> > > what will be >> >> > > the credibility of these messages? We will just ignore these messages >> >> > > when >> >> > > these issues you mention actually appears because we see them >> >> > > everytime >> >> > > on >> >> > > reboot or shutdown. >> >> > >> >> > I would agree that if these messages are expected to be seen every >> >> > time, there's no way to fix them, and they're not indicative of any >> >> > problem then something should be done. Seeing something printed at >> >> > "dev_error" level with an exclamation point (!) at the end makes me >> >> > feel like this is something that needs immediate action on my part. >> >> > >> >> > If we really can't do better but feel that the messages need to be >> >> > there, at least make them dev_info and less scary like: >> >> > >> >> > arm-smmu 15000000.iommu: turning off; DMA should be quiesced before >> >> > now >> >> > >> >> > ...that would still give you a hint in the logs that if you saw a DMA >> >> > transaction after the message that it was a bug but also wouldn't >> >> > sound scary to someone who wasn't seeing any other problems. >> >> > >> >> >> >> We can do this if Robin is OK? >> > >> > It would be nice if you could figure out which domains are still live >> > when >> > the SMMU is being shut down in your case and verify that it *is* infact >> > benign before we start making the message more friendly. As Robin said >> > earlier, rogue DMA is a real nightmare to debug. >> > >> >> I could see this error message for all the clients of apps_smmu. >> I checked manually enabling bypass and removing iommus dt property >> for each client of apps_smmu. > > Any update on the status here? If I'm reading the conversation above, > Robin said: "we'll *always* see the warning because there's no way to > tear down the default DMA domains, and even if all devices *have* been > nicely quiesced there's no way to tell". Did I understand that > properly? If so, it seems like it's fully expected to see this > message on every reboot and it doesn't necessarily signify anything > bad. > Understanding is the same, waiting for Will and Robin to check if its OK to make the message more friendly. -Sai -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu