linux-kernel - Re: [PATCH 1/3] iommu: Add Visconti5 IOMMU driver

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Date:   Wed, 25 May 2022 22:40:00 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     Baolu Lu <baolu.lu@...ux.intel.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "yuji2.ishikawa@...hiba.co.jp" <yuji2.ishikawa@...hiba.co.jp>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@...hiba.co.jp>,
        Will Deacon <will@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/3] iommu: Add Visconti5 IOMMU driver

On Thu, May 26, 2022 at 12:43:25AM +0000, Tian, Kevin wrote:

> iiuc then this suggests there should be only one iommu group per atu,
> instead of using generic_device_group() to create one group per
> device.

Sounds like it

> > rejected then this driver should have a IOMMU_DOMAIN_BLOCKING and
> > return that from ops->def_domain_type().
> 
> BLOCKING should not be used as a default domain type for DMA API
> which needs either a DMA or IDENTITY type.

New drivers should not have a NULL group->default_domain. 

IMHO this driver does not support the DMA API so the default_domain
should be assigned to blocking and the DMA API disabled. We might need
some core changes to accommodate this.

The alternative would be to implement the identity domain, assuming
the ATU thing can store that kind of translation.

Jason