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

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Date:   Thu, 30 Jun 2022 17:33:16 +0800
From:   Yong Wu <yong.wu@...iatek.com>
To:     Nicolin Chen <nicolinc@...dia.com>
CC:     "Tian, Kevin" <kevin.tian@...el.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Baolu Lu <baolu.lu@...ux.intel.com>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "cohuck@...hat.com" <cohuck@...hat.com>,
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Subject: Re: [PATCH v3 1/5] iommu: Return -EMEDIUMTYPE for incompatible
 domain and device/group

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