On 04/29/2013 04:34 PM, Duran, Leo wrote:This sounds more like issue with the order of how things are initialized in the system.I'm wondering if resetting the IOMMU at init-time (once) would clear any BIOS induced noise.Well, depends what you mean by 'reset'....
(a) setting it up for OS use is effectively a reset, but doesn't quiesce a device
doing dma reads of a (bios-setup) queue. then the noisy messages begin
(b) disable the iommu, and then the dma just occurs... and bad for writes, potentially.
Similar issue is being reported & worked for kdump, where device are still
doing DMA while the system is trying to 'reset' to the kexec'd kernel, and
take a crash dump.
Solution: stop devices from doing dma... but some you _want_ enabled throughout...
like keyboard & mouse via usb controller, so you get to pick os from
grub... not so for kexec...
so, again, for isolation faults.... let the hw do its job -- isolate
and throttle/silence the fault messages on a per-device, time-duration heuristic
so the system can get through boot-up where enough OS is init'd (drivers started)
to stop the temporary noise.