linux-kernel - Re: [RFC PATCH v1 0/6] Resolve unwanted DMA backing with IOMMU

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Message-ID: <20180727183134.GD6738@8bytes.org>
Date:   Fri, 27 Jul 2018 20:31:34 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     Dmitry Osipenko <digetx@...il.com>,
        Will Deacon <will.deacon@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Jon Hunter <jonathanh@...dia.com>,
        Mikko Perttunen <cyndis@...si.fi>,
        Frank Rowand <frowand.list@...il.com>, bskeggs@...hat.com,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>, kwizart@...il.com,
        devicetree@...r.kernel.org, nouveau@...ts.freedesktop.org,
        Linux IOMMU <iommu@...ts.linux-foundation.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-tegra@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v1 0/6] Resolve unwanted DMA backing with IOMMU

On Fri, Jul 27, 2018 at 11:13:31AM -0600, Rob Herring wrote:
> I don't follow why we need a property rather than being implied by the
> device's (the GPU) compatible string.

There might be devices where either setup works, with or without IOMMU
translation, and the firmware can set the property depending on whether
the user wants more performance or more security.

If we have a whitelist in the kernel this gets more complicated, we
probably need additional kernel-parameters to overwrite those whitelist
entries. Having a property in the device-tree seems to be a better way
here, imho.


	Joerg