linux-kernel - Re: [PATCH v4 08/11] iommu/mediatek: Add a gap for the iova regions

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Message-ID: <7e108286-4ada-fdf3-cabc-aa3ce61117a6@collabora.com>
Date:   Wed, 15 Feb 2023 13:35:43 +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, jianjiao.zeng@...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 v4 08/11] iommu/mediatek: Add a gap for the iova regions

Il 15/02/23 07:25, Yong Wu ha scritto:
> As the removed property in the vcodec dt-binding, the property is:
> dma-ranges = <0x1 0x0 0x0 0x40000000 0x0 0xfff00000>;
> 
> The length is 0xfff0_0000 rather than 0x1_0000_0000, this means it
> requires 1M as a gap. This is because the end address for some vcodec
> HW is (address + size). If the size is 4G, the end address may be
> 0x2_0000_0000, and the width for vcodec register only is 32, then the
> HW may get the ZERO address.
> 
> Currently the consumer's dma-ranges property doesn't work, IOMMU
> has to consider this case. Add a bigger gap(8M) for all the regions
> to avoid it.
> 
> Signed-off-by: Yong Wu <yong.wu@...iatek.com>
> Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
> ---
> Hi AngeloGioacchino,
> I define a new macro for this, I think it is a small change, thus keep
> you R-b.
> Thanks.

Hello!
You added a nice comment to the new definition describing that there's a 8M gap,
so it's completely fine; you can keep my R-b on this one just fine!

Regards,
Angelo