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From:   Evan Green <evgreen@chromium.org>
Date:   Tue, 19 Feb 2019 15:29:41 -0800
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Subject: Re: [PATCH v6 06/22] iommu/io-pgtable-arm-v7s: Extend MediaTek 4GB Mode
To:     Yong Wu <yong.wu@mediatek.com>
Cc:     Joerg Roedel <joro@8bytes.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Robin Murphy <robin.murphy@arm.com>,
        Rob Herring <robh+dt@kernel.org>,
        Tomasz Figa <tfiga@google.com>,
        Will Deacon <will.deacon@arm.com>,
        linux-mediatek@lists.infradead.org, srv_heupstream@mediatek.com,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        linux-arm-kernel@lists.infradead.org,
        iommu@lists.linux-foundation.org, yingjoe.chen@mediatek.com,
        youlin.pei@mediatek.com, Nicolas Boichat <drinkcat@chromium.org>,
        anan.sun@mediatek.com, Matthias Kaehlcke <mka@chromium.org>
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On Sun, Feb 17, 2019 at 1:07 AM Yong Wu <yong.wu@mediatek.com> wrote:
>
> MediaTek extend the arm v7s descriptor to support the dram over 4GB.
>
> In the mt2712 and mt8173, it's called "4GB mode", the physical address
> is from 0x4000_0000 to 0x1_3fff_ffff, but from EMI point of view, it
> is remapped to high address from 0x1_0000_0000 to 0x1_ffff_ffff, the
> bit32 is always enabled. thus, in the M4U, we always enable the bit9
> for all PTEs which means to enable bit32 of physical address.
>
> but in mt8183, M4U support the dram from 0x4000_0000 to 0x3_ffff_ffff
> which isn't remaped. We extend the PTEs: the bit9 represent bit32 of
> PA and the bit4 represent bit33 of PA. Meanwhile the iova still is
> 32bits.
>
> In order to unify code, in the "4GB mode", we add the bit32 for the
> physical address manually in our driver.
>
> Correspondingly, Adding bit32 and bit33 for the PA in the iova_to_phys
> has to been moved into v7s.
>
> Regarding whether the pagetable address could be over 4GB, the mt8183
> support it while the previous mt8173 don't. thus keep it as is.
>
> Signed-off-by: Yong Wu <yong.wu@mediatek.com>
> Reviewed-by: Robin Murphy <robin.murphy@arm.com>
> ---
> Comparing the previous version, I add MTK_4GB quirk always since mtk_iommu
> has already controlled the PA itself. Helped from Evan.

Thanks for all the explanation on this one. I think I understand it
now, and it looks good to me.

Reviewed-by: Evan Green <evgreen@chromium.org>