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

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Message-ID: <35937e036d7d62f048b84c0f1ea6e98136e7ad5c.camel@mediatek.com>
Date:   Tue, 14 Feb 2023 05:33:28 +0000
From:   Yong Wu (吴勇) <Yong.Wu@...iatek.com>
To:     "joro@...tes.org" <joro@...tes.org>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "mchehab@...nel.org" <mchehab@...nel.org>,
        "angelogioacchino.delregno@...labora.com" 
        <angelogioacchino.delregno@...labora.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>
CC:     "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Youlin Pei (裴友林) 
        <youlin.pei@...iatek.com>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Anan Sun (孙安安) <Anan.Sun@...iatek.com>,
        Libo Kang (康利波) <Libo.Kang@...iatek.com>,
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        Chengci Xu (许承赐) 
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        YF Wang (王云飞) <YF.Wang@...iatek.com>,
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        <krzysztof.kozlowski+dt@...aro.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        Mingyuan Ma (马鸣远) 
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        "nfraprado@...labora.com" <nfraprado@...labora.com>
Subject: Re: [PATCH 07/10] iommu/mediatek: Add a gap for the iova regions

On Mon, 2023-01-16 at 10:46 +0100, AngeloGioacchino Del Regno wrote:
> 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... 

Thanks very much for your review.

> 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).

I got a real vcodec issue described in the commit message. As you may
see in the vcodec's dt-binding example[1/10] or the dts node[9/10],
their length is 0xfff00000 that means they use 1M as the gap. Vcodec
use this for a long time. After this patchset, this property is unused,
then I have to take care this in the iommu, therefore this patch is
required, and I just give a bigger gap(8M) here.

> 
> Ideas?
> 
> Regards,
> Angelo
>