linux-kernel - Re: [PATCH v1 3/4] iommu/tegra: gart: Constify number of GART pages

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Message-ID: <20180427094953.GN30388@ulmo>
Date:   Fri, 27 Apr 2018 11:49:53 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Jonathan Hunter <jonathanh@...dia.com>,
        Joerg Roedel <joro@...tes.org>,
        iommu@...ts.linux-foundation.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 3/4] iommu/tegra: gart: Constify number of GART pages

On Mon, Apr 09, 2018 at 11:07:21PM +0300, Dmitry Osipenko wrote:
> GART has a fixed aperture size, hence the number of pages is constant.
> 
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
>  drivers/iommu/tegra-gart.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)

This doesn't really give a good explanation of why you want to do this.
While it is certainly true that the aperture is fixed in size, I can
imagine cases where somebody would want to restrict the aperture size
(perhaps there's a fixed mapping somewhere near the end of the mapping
that Linux shouldn't touch, or the GART aperture could be reduced to
simulate out of IOVA memory situations).

Without a good explanation why this is necessary I don't see why the
current code should be changed.

Thierry

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