linux-kernel - Re: [PATCH 06/13] drm/etnaviv: Use sychronized interface of the IOMMU-API

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Message-ID: <20170817141858.GG16908@8bytes.org>
Date:   Thu, 17 Aug 2017 16:18:58 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Lucas Stach <l.stach@...gutronix.de>
Cc:     Joerg Roedel <jroedel@...e.de>, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org,
        Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
        Russell King <linux+etnaviv@...linux.org.uk>,
        Christian Gmeiner <christian.gmeiner@...il.com>,
        David Airlie <airlied@...ux.ie>, etnaviv@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 06/13] drm/etnaviv: Use sychronized interface of the
 IOMMU-API

On Thu, Aug 17, 2017 at 04:03:54PM +0200, Lucas Stach wrote:
> There is no IOMMU driver in use. Etnaviv just uses part of the IOMMU API
> to manage the GPU internal MMU, see
> drivers/gpu/drm/etnaviv/etnaviv_iommu.c

That looks like a very fragile construct, because it relies on internal
behavior of the iommu code that can change in the future.

I strongly suggest to either make etnaviv_iommu.c a real iommu driver an
move it to drivers/iommu, or (prefered by me) just call directly into
the map/unmap functions of this driver from the rest of the
etnaviv_iommu.c. I don't really see a reason why the IOMMU-API needs to
be used there as another layer of indirection.

Regards,

	Joerg