linux-kernel - Re: [RFC PATCH] iommu: arm-smmu-nvidia: Add default domain type implementation op

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Message-ID: <ZKxQnKhqKziyxX8f@ziepe.ca>
Date:   Mon, 10 Jul 2023 15:40:28 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Stanimir Varbanov <svarbanov@...e.de>
Cc:     linux-tegra@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Thierry Reding <thierry.reding@...il.com>,
        Krishna Reddy <vdumpa@...dia.com>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [RFC PATCH] iommu: arm-smmu-nvidia: Add default domain type
 implementation op

On Mon, Jul 10, 2023 at 11:22:52AM +0300, Stanimir Varbanov wrote:
> Add def_domain_type implementation op and override default IOMMU
> domain Kconfig option (CONFIG_IOMMU_DEFAULT_PASSTHROUGH=y), which
> could be enabled on some distros. The current quirk has been done
> for Tegra234 machine, because I found the issue on it. The issue
> itself appears on USB host controller which cannot be initialized
> without IOMMU translation. Something more, we proved that IOMMU
> translation is needed for display and GPU drivers as well.

Generically, if you find HW combinations where certain end points
cannot work with passthrough (which is really weird in the first
place) it should be narrowly quirked - not just an entire platform.

Also we don't really have a way to force non-passthrough, ARM32
systems will always run in passthrough, for instance. Broadly the
kernel expects it to work.

Jason