Date:   Mon, 14 Aug 2023 16:21:31 +0800
From:   Chen-Yu Tsai <wenst@...omium.org>
To:     Yong Wu (吴勇) <Yong.Wu@...iatek.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Jianjiao Zeng (曾健姣) 
        <Jianjiao.Zeng@...iatek.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "joro@...tes.org" <joro@...tes.org>,
        Chengci Xu (许承赐) 
        <Chengci.Xu@...iatek.com>,
        YF Wang (王云飞) <YF.Wang@...iatek.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        Mingyuan Ma (马鸣远) 
        <Mingyuan.Ma@...iatek.com>,
        "angelogioacchino.delregno@...labora.com" 
        <angelogioacchino.delregno@...labora.com>,
        "will@...nel.org" <will@...nel.org>
Subject: Re: [PATCH v12 5/7] iommu/mediatek: Add MT8188 IOMMU Support

On Mon, Aug 14, 2023 at 3:14 PM Yong Wu (吴勇) <Yong.Wu@...iatek.com> wrote:
>
> On Fri, 2023-08-11 at 11:30 +0800, Chen-Yu Tsai wrote:
> >
> > External email : Please do not click links or open attachments until
> > you have verified the sender or the content.
> >  On Thu, Aug 10, 2023 at 8:23 PM Yong Wu (吴勇) <Yong.Wu@...iatek.com>
> > wrote:
> > >
> > > On Tue, 2023-08-08 at 17:53 +0800, Chen-Yu Tsai wrote:
> > > >
> > > > External email : Please do not click links or open attachments
> > until
> > > > you have verified the sender or the content.
> > > >  On Fri, Jun 2, 2023 at 5:04 PM Yong Wu <yong.wu@...iatek.com>
> > wrote:
> > > > >
> > > > > From: "Chengci.Xu" <chengci.xu@...iatek.com>
> > > > >
> > > > > MT8188 has 3 IOMMU, containing 2 MM IOMMUs, one is for vdo, the
> > > > other
> > > > > is for vpp. and 1 INFRA IOMMU.
> > > > >
> > > > > Signed-off-by: Chengci.Xu <chengci.xu@...iatek.com>
> > > > > Signed-off-by: Yong Wu <yong.wu@...iatek.com>
> > > > > Reviewed-by: AngeloGioacchino Del Regno <
> > > > angelogioacchino.delregno@...labora.com>
> > > > > ---
> > > > >  drivers/iommu/mtk_iommu.c | 49
> > > > +++++++++++++++++++++++++++++++++++++++
> > > > >  1 file changed, 49 insertions(+)
> > > > >
> > > > > diff --git a/drivers/iommu/mtk_iommu.c
> > b/drivers/iommu/mtk_iommu.c
> > > > > index 9c89cf894a4d..5c66af0c45a8 100644
> > > > > --- a/drivers/iommu/mtk_iommu.c
> > > > > +++ b/drivers/iommu/mtk_iommu.c
> > > > > @@ -170,6 +170,7 @@ enum mtk_iommu_plat {
> > > > >         M4U_MT8173,
> > > > >         M4U_MT8183,
> > > > >         M4U_MT8186,
> > > > > +       M4U_MT8188,
> > > > >         M4U_MT8192,
> > > > >         M4U_MT8195,
> > > > >         M4U_MT8365,
> > > > > @@ -1593,6 +1594,51 @@ static const struct mtk_iommu_plat_data
> > > > mt8186_data_mm = {
> > > > >         .iova_region_larb_msk = mt8186_larb_region_msk,
> > > > >  };
> > > > >
> > > > > +static const struct mtk_iommu_plat_data mt8188_data_infra = {
> > > > > +       .m4u_plat         = M4U_MT8188,
> > > > > +       .flags            = WR_THROT_EN | DCM_DISABLE |
> > > > STD_AXI_MODE | PM_CLK_AO |
> > > > > +                           MTK_IOMMU_TYPE_INFRA |
> > > > IFA_IOMMU_PCIE_SUPPORT |
> > > > > +                           PGTABLE_PA_35_EN |
> > > > CFG_IFA_MASTER_IN_ATF,
> > > >
> > > > FWIW, CFG_IFA_MASTER_IN_ATF should not be tied to the compatible
> > > > string,
> > > > but set via a DT property. The IOMMU controls are secured by
> > > > firmware.
> > > > It is not a property intrinsically tied to the hardware.
> > >
> > > The flag CFG_IFA_MASTER_IN_ATF means the registers which
> > enable/disable
> > > iommu are in the secure world. If the master like pcie want to
> > enable
> > > iommu, we have to enter secure world to configure it. It should be
> > HW
> > > intrinsical, right?
> >
> > If I understand correctly, this is forced by setting some registers.
> > The registers are set by the firmware at boot time.
>
> The register will be set before the masters that have the "iommus="
> property probe. If the master doesn't have "iommus=" property in its
> dtsi node, this register won't be set, then its iommu will be disabled
> and it has to access continuous buffer.
>
> >
> > So if a different firmware that doesn't set the registers is used,
> > then the IOMMU is available to non-secure kernel, correct?
>
> No. The meaning of this register is whether to enable iommu. If the
> register are not set, the IOMMU for that master is disabled.

For clarity, I'm referring to PERI_MST_PROT [1], not the registers in the
IOMMU or LARBs. So not any of the registers used in this patch.

If that register doesn't restrict access to IOMMU register space to secure
only, then I assume it is controlled by fuses?

[1] https://review.trustedfirmware.org/plugins/gitiles/TF-A/trusted-firmware-a/+/be457248c6b0a7f3c61bd95af58372938d13decd/plat/mediatek/drivers/iommu/mt8188/mtk_iommu_plat.c#93

> >
> > That's why I said that it should not be tied to a particular hardware
> > platform, but set using a boolean device tree property.
> >
> > > >
> > > > If on some other project there is no such security requirement
> > and
> > > > the
> > > > IOMMU is opened up to non-secure world, and ATF not even having
> > > > support
> > > > for the SMC call, this becomes unusable and hard to rectify
> > without
> > > > introducing a new compatible string.
> > > >
> > > > ChenYu
> > > >

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