linux-kernel - Re: [PATCH 07/10] iommu/mediatek: Add a gap for the iova regions

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Message-ID: <1a9a09d5-58e2-badc-6d1c-fe2008c305f9@collabora.com>
Date:   Mon, 16 Jan 2023 10:46:16 +0100
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Yong Wu <yong.wu@...iatek.com>, Joerg Roedel <joro@...tes.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>
Cc:     Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Hans Verkuil <hverkuil@...all.nl>, nfraprado@...labora.com,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
        iommu@...ts.linux.dev, mingyuan.ma@...iatek.com,
        yf.wang@...iatek.com, libo.kang@...iatek.com,
        Yunfei Dong <yunfei.dong@...iatek.com>,
        kyrie wu <kyrie.wu@...iatek.corp-partner.google.com>,
        chengci.xu@...iatek.com, youlin.pei@...iatek.com,
        anan.sun@...iatek.com
Subject: Re: [PATCH 07/10] iommu/mediatek: Add a gap for the iova regions

Il 13/01/23 07:01, Yong Wu ha scritto:
> Currenly masters can not indicate its special dma-ranges. Prepare
> for vcodec. some vcodec end address is address + size, if our size
> is 4G, the end address may be 0x2_0000_0000. and the
> register is u32, then it may get zero. thus add a gap(8M) for
> all the regions.
> 
> Signed-off-by: Yong Wu <yong.wu@...iatek.com>

I definitely agree on the fact that we do *need* this series... but this
particular commit looks like a hack.

I'm not convinced: I have a hunch that this one will sooner or later backfire
on us and break things again... at the same time, I'm not sure how to do this
properly at this point (I didn't do any research, anyway).

Ideas?

Regards,
Angelo