[PATCH v3 1/5] iommu: Return -EMEDIUMTYPE for incompatible domain and device/group

[Yong Wu]

On Wed, 2022-06-29 at 12:47 -0700, Nicolin Chen wrote:
> On Fri, Jun 24, 2022 at 03:19:43PM -0300, Jason Gunthorpe wrote:
> > On Fri, Jun 24, 2022 at 06:35:49PM +0800, Yong Wu wrote:
> > 
> > > > > It's not used in VFIO context. "return 0" just satisfy the
> > > > > iommu
> > > > > framework to go ahead. and yes, here we only allow the shared
> > > > > "mapping-domain" (All the devices share a domain created
> > > > > internally).
> > 
> > What part of the iommu framework is trying to attach a domain and
> > wants to see success when the domain was not actually attached ?
> > 
> > > > What prevent this driver from being used in VFIO context?
> > > 
> > > Nothing prevent this. Just I didn't test.
> > 
> > This is why it is wrong to return success here.
> 
> Hi Yong, would you or someone you know be able to confirm whether
> this "return 0" is still a must or not?
> 
> Considering that it's an old 32-bit platform for MTK, if it would
> take time to do so, I'd like to drop the change in MTK driver and
> note in commit log for you or other MTK folks to change in future.

Yes. Please help drop the change in this file.

Sorry I don't have the board at hand right now and I could not list the
backtrace where this is needed(should be bus_iommu_probe from the
previous debug...)

> 
> Thanks
> Nic