Re: Device specific pass through in host systems - discuss user interface

["Raj, Ashok" <ashok.raj@intel.com>]

On Mon, Jun 10, 2019 at 09:38:11PM -0700, Sai Praneeth Prakhya wrote:
> Hi All,
> 
> + Sohil and Rob Clark (as there are dropped from CC'list)
> 
> > > > Most iommu vendor drivers have switched from per-device to per-group
> > > > domain (a.k.a. default domain). So per-group pass-through mode makes
> > more sense?
> > > >
> > > > By the way, can we extend this to "per-group default domain type",
> > > > instead of only "per-group pass-through mode"? Currently we have
> > > > system level default domain type, if we have finer granularity of
> > > > default domain type, both iommu drivers and end users will benefit from it.
> > >
> > > Sure! Makes sense.. per-group default domain type sounds good.
> 
> I am planning to implement an RFC (supporting only runtime case for now) which works as below
> 
> 1. User unbinds the driver by writing to sysfs
> 2. User puts a group in pass through mode by writing "1" to
> /sys/kernel/iommu_groups/<group_id>/pt

might be better to read current value of default domain for that group.. 
/sys/kernel/iommu_groups/<group_id>/default_domain

reading the above value shows current setting.
provide a differnet file next_def_domain, and you can echo "pt" or "dma_domain"
to switch to pass-through, or normal dma isolation mode.

For devices that automatically set to pass through today like graphics, or isoch audio
you can show "pt" as default_domain.
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