Hi, On Tue, Mar 31, 2020 at 12:53 AM Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx> 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. -Doug
