linux-kernel - Re: [PATCH v9 2/7] iommu/mediatek: Fix two IOMMU share pagetable issue

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Message-ID: <47cac7a6-c069-64a2-7979-b879b075058f@collabora.com>
Date:   Fri, 17 Mar 2023 10:34:00 +0100
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Yong Wu <yong.wu@...iatek.com>, Joerg Roedel <joro@...tes.org>,
        Will Deacon <will@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>
Cc:     Robin Murphy <robin.murphy@....com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        iommu@...ts.linux.dev, linux-mediatek@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, mingyuan.ma@...iatek.com,
        yf.wang@...iatek.com, jianjiao.zeng@...iatek.com,
        chengci.xu@...iatek.com
Subject: Re: [PATCH v9 2/7] iommu/mediatek: Fix two IOMMU share pagetable
 issue

Il 17/03/23 09:55, Yong Wu ha scritto:
> From: "Chengci.Xu" <chengci.xu@...iatek.com>
> 
> Prepare for mt8188 to fix a two IOMMU HWs share pagetable issue.
> 
> We have two MM IOMMU HWs in mt8188, one is VPP-IOMMU, another is VDO-IOMMU.
> The 2 MM IOMMU HWs share pagetable don't work in this case:
>   a) VPP-IOMMU probe firstly.
>   b) VDO-IOMMU probe.
>   c) The master for VDO-IOMMU probe (means frstdata is vpp-iommu).
>   d) The master in another domain probe. No matter it is vdo or vpp.
> Then it still create a new pagetable in step d). The problem is
> "frstdata->bank[0]->m4u_dom" was not initialized. Then when d) enter, it
> still create a new one.
> 
> In this patch, we create a new variable "share_dom" for this share
> pgtable case, it should be helpful for readable. and put all the share
> pgtable logic in the mtk_iommu_domain_finalise.
> 
> In mt8195, the master of VPP-IOMMU probes before than VDO-IOMMU
> from its dtsi node sequence, we don't see this issue in it. Prepare for
> mt8188.
> 
> Signed-off-by: Chengci.Xu <chengci.xu@...iatek.com>
> Signed-off-by: Yong Wu <yong.wu@...iatek.com>

I'm not sure whether this is *not* a fix... if a specific platform wasn't
affected, this may still be a logic mistake... to be cautious, I would
still add a Fixes tag to this one.

Otherwise, I would reword the commit title and remove the "Fix" word, so
that it would look something like...

iommu/mediatek: Prepare for pagetables domain sharing

I'm sorry for noticing that only at v9, but the previous versions had a bit
more stuff to address and couldn't really focus on analyzing this one.

If there's anything I've misunderstood about this patch, please feel free
to explain.

Regards,
Angelo