Subject: Re: [PATCH v3 12/33] iommu/mediatek: Always tlb_flush_all when each
 PM resume
To:     Yong Wu <yong.wu@mediatek.com>, Joerg Roedel <joro@8bytes.org>,
        Rob Herring <robh+dt@kernel.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Will Deacon <will@kernel.org>,
        Robin Murphy <robin.murphy@arm.com>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>,
        Tomasz Figa <tfiga@chromium.org>,
        linux-mediatek@lists.infradead.org, srv_heupstream@mediatek.com,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        iommu@lists.linux-foundation.org,
        Hsin-Yi Wang <hsinyi@chromium.org>, youlin.pei@mediatek.com,
        anan.sun@mediatek.com, chao.hao@mediatek.com,
        yen-chang.chen@mediatek.com
References: <20210923115840.17813-1-yong.wu@mediatek.com>
 <20210923115840.17813-13-yong.wu@mediatek.com>
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>
Message-ID: <5228acea-3bf4-987a-caaf-11b90aa0beae@collabora.com>
Date:   Tue, 4 Jan 2022 16:55:39 +0100
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Il 23/09/21 13:58, Yong Wu ha scritto:
> Prepare for 2 HWs that sharing pgtable in different power-domains.
> 
> When there are 2 M4U HWs, it may has problem in the flush_range in which
> we get the pm_status via the m4u dev, BUT that function don't reflect the
> real power-domain status of the HW since there may be other HW also use
> that power-domain.
> 
> The function dma_alloc_attrs help allocate the iommu buffer which
> need the corresponding power domain since tlb flush is needed when
> preparing iova. BUT this function only is for allocating buffer,
> we have no good reason to request the user always call pm_runtime_get
> before calling dma_alloc_xxx. Therefore, we add a tlb_flush_all
> in the pm_runtime_resume to make sure the tlb always is clean.
> 
> Another solution is always call pm_runtime_get in the tlb_flush_range.
> This will trigger pm runtime resume/backup so often when the iommu
> power is not active at some time(means user don't call pm_runtime_get
> before calling dma_alloc_xxx), This may cause the performance drop.
> thus we don't use this.
> 
> In other case, the iommu's power should always be active via device
> link with smi.
> 
> The previous SoC don't have PM except mt8192. the mt8192 IOMMU is display's
> power-domain which nearly always is enabled. thus no need fix tags here.
> Prepare for mt8195.
> 
> Signed-off-by: Yong Wu <yong.wu@mediatek.com>

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>