[dpdk-dev] [EXT] Re: [PATCH] bus/pci: fix IOVA as VA mode selection

[Thomas Monjalon]

09/07/2019 16:37, Burakov, Anatoly:
> My view would be to always run in IOVA as VA by default and only falling 
> back to IOVA as PA if there is a need to do that. Yet, it seems that 
> whenever i try to bring this up, the response (not necessarily from you, 
> so this is not directed at you specifically) seems to be that because of 
> hotplug, we have to start in the "safest" (from device support point of 
> view) mode - that is, in IOVA as PA. Seeing how, as you claim, some 
> devices require IOVA as VA, then IOVA as PA is no longer the "safe" 
> default that all devices will support. Perhaps we can use this 
> opportunity to finally make IOVA as VA the default :)

That's a good point Anatoly. We need to decide what is the safest default.

About the capabilities flags, please let's agree that we want
to express 3 cases, so we need 2 flags.
About the preference of a mode for a device, if a mode is really
bad for a device, I suggest to not advertise it in capabilities.

In order to take a better decision, we need a summary of the
decision algorithm per layer, involving kernel driver capabilities
and memory capabilities.