linux-kernel - Re: [PATCH v1 1/3] gpu: host1x: Remove implicit IOMMU backing on client's registration

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Message-ID: <e7ecff74-ef8e-fd7e-1be2-0f3c60abc6f8@gmail.com>
Date:   Mon, 24 Jun 2019 15:55:04 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        dri-devel@...ts.freedesktop.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/3] gpu: host1x: Remove implicit IOMMU backing on
 client's registration

24.06.2019 10:04, Christoph Hellwig пишет:
> Don't we have a device tree problem here if there is a domain covering
> them?  I though we should only pick up an IOMMU for a given device
> if DT explicitly asked for that?
> 

There is no specific domain that "covering them". The IOMMU domain is allocated
dynamically during of the Tegra DRM's driver initialization (see tegra_drm_load) and
then all of DRM devices are attached to that domain once all of the DRM sub-drivers
are probed successfully. On Tegra SoCs it's up to software (driver) to decide how to
separate hardware devices from each other, in a case of DRM we're putting all the
relevant graphics devices into a single domain. Is it even possible to express IOMMU
domain (not group!) assignments in a device-tree?