Messages in this thread | | | Date | Thu, 23 Apr 2020 13:47:03 +0530 | From | Sai Prakash Ranjan <> | Subject | Re: [PATCH] iommu/arm-smmu: Demote error messages to debug in shutdown callback |
| |
Hi,
On 2020-04-23 01:19, Doug Anderson wrote: > Hi, > > On Tue, Mar 31, 2020 at 12:53 AM Sai Prakash Ranjan > <saiprakash.ranjan@codeaurora.org> 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 >> >> > <saiprakash.ranjan@codeaurora.org> 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
| |