linux-kernel - Re: [PATCH v5 10/20] iommu/mediatek: Move reset_axi into plat

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Date:   Wed, 30 Jan 2019 10:30:18 -0800
From:   Evan Green <evgreen@...omium.org>
To:     Yong Wu <yong.wu@...iatek.com>
Cc:     Joerg Roedel <joro@...tes.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Robin Murphy <robin.murphy@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Tomasz Figa <tfiga@...gle.com>,
        Will Deacon <will.deacon@....com>,
        linux-mediatek@...ts.infradead.org, srv_heupstream@...iatek.com,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org, Arnd Bergmann <arnd@...db.de>,
        yingjoe.chen@...iatek.com, youlin.pei@...iatek.com,
        Nicolas Boichat <drinkcat@...omium.org>
Subject: Re: [PATCH v5 10/20] iommu/mediatek: Move reset_axi into plat_data

On Mon, Dec 31, 2018 at 7:58 PM Yong Wu <yong.wu@...iatek.com> wrote:
>
> In mt8173 and mt8183, 0x48 is REG_MMU_STANDARD_AXI_MODE while
> it is extended to REG_MMU_CTRL which contains _STANDARD_AXI_MODE in
> the other SoCs. I move this property to plat_data since both mt8173
> and mt8183 use this property.
>
> It is a preparing patch for mt8183.
>
> Signed-off-by: Yong Wu <yong.wu@...iatek.com>
> ---
>  drivers/iommu/mtk_iommu.c | 4 ++--
>  drivers/iommu/mtk_iommu.h | 2 +-
>  2 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
> index 35a1263..8d8ab21 100644
> --- a/drivers/iommu/mtk_iommu.c
> +++ b/drivers/iommu/mtk_iommu.c
> @@ -558,8 +558,7 @@ static int mtk_iommu_hw_init(const struct mtk_iommu_data *data)
>         }
>         writel_relaxed(0, data->base + REG_MMU_DCM_DIS);
>
> -       /* It's MISC control register whose default value is ok except mt8173.*/
> -       if (data->plat_data->m4u_plat == M4U_MT8173)
> +       if (data->plat_data->reset_axi)
>                 writel_relaxed(0, data->base + REG_MMU_STANDARD_AXI_MODE);

The commit description makes it sound like the overall format of the
register is the same, but the "other SoCs" have some extra bits they'd
like to leave alone. Would it be easier to do a read-modify-write to
always clear some bits in the register, instead of doing something
based on the SoC? Or do the bits mean completely different things in
the different versions (in which case what you've got makes sense to
me)?
-Evan