linux-kernel - Re: [PATCH v2 4/7] iommu: Let iommu.strict override ops->def_domain

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Message-ID: <Y4ZCVgLO9AHatwXe@nvidia.com>
Date:   Tue, 29 Nov 2022 13:33:10 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Niklas Schnelle <schnelle@...ux.ibm.com>,
        Baolu Lu <baolu.lu@...ux.intel.com>,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        Gerd Bayer <gbayer@...ux.ibm.com>, iommu@...ts.linux.dev,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Wenjia Zhang <wenjia@...ux.ibm.com>,
        Pierre Morel <pmorel@...ux.ibm.com>,
        linux-s390@...r.kernel.org, borntraeger@...ux.ibm.com,
        hca@...ux.ibm.com, gor@...ux.ibm.com,
        gerald.schaefer@...ux.ibm.com, agordeev@...ux.ibm.com,
        svens@...ux.ibm.com, linux-kernel@...r.kernel.org,
        Julian Ruess <julianr@...ux.ibm.com>
Subject: Re: [PATCH v2 4/7] iommu: Let iommu.strict override
 ops->def_domain_type

On Mon, Nov 28, 2022 at 09:01:43PM +0000, Robin Murphy wrote:

> I'm hardly an advocate for trying to save users from themselves, but I
> honestly can't see any justifiable reason for not having sysfs respect
> iommu_get_def_domain_type(). 

We really need to rename this value if it is not actually just an
advisory "default" but a functional requirement ..

> > The driver should have no say in how dma-iommu.c works beyond if it
> > provides the required ops functionalities, and hint(s) as to what
> > gives best performance.
> 
> That should already be the case today, as outlined in my other mail. It's
> just somewhat more evolved than designed, so may not be so clear to
> everyone.

It is close to being clear, once we get the last touches of dma-iommu
stuff out of the drivers it should be quite clear

Thanks,
Jason