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From: Tomasz Figa <tfiga@chromium.org>
Date: Fri, 10 Jun 2016 15:22:56 +0900
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Subject: Re: [PATCH v2 4/7] ARM: dts: rockchip: add virtual iommu for display
To: Shunqian Zheng <zhengsq@rock-chips.com>
Cc: Joerg Roedel <joro@8bytes.org>,
        =?UTF-8?Q?Heiko_St=C3=BCbner?= <heiko@sntech.de>,
        Rob Herring <robh+dt@kernel.org>, Mark Rutland <mark.rutland@arm.com>,
        linux@armlinux.org.uk,
        =?UTF-8?B?5aea5pm65oOF?= <mark.yao@rock-chips.com>,
        David Airlie <airlied@linux.ie>, simon xue <xxm@rock-chips.com>,
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	<linux-arm-kernel@lists.infradead.org>,
        "open list:IOMMU DRIVERS" <iommu@lists.linux-foundation.org>,
        devicetree@vger.kernel.org,
        dri-devel <dri-devel@lists.freedesktop.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@lists.infradead.org>
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Hi,

On Wed, Jun 8, 2016 at 10:26 PM, Shunqian Zheng <zhengsq@rock-chips.com> wrote:
> An virtual iommu without reg or interrupts for display.
> Adding this according to iommu driver changes.
>
> Signed-off-by: Shunqian Zheng <zhengsq@rock-chips.com>
> ---
>  arch/arm/boot/dts/rk3288.dtsi | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/arch/arm/boot/dts/rk3288.dtsi b/arch/arm/boot/dts/rk3288.dtsi
> index 7fa932f..4cd535f 100644
> --- a/arch/arm/boot/dts/rk3288.dtsi
> +++ b/arch/arm/boot/dts/rk3288.dtsi
> @@ -219,9 +219,15 @@
>                 clock-names = "timer", "pclk";
>         };
>
> +       display_mmu: virtual-iommu {
> +               compatible = "rockchip,iommu";
> +               #iommu-cells = <0>;
> +       };
> +

Device tree should describe real hardware and so it isn't really a
good idea to add such virtual iommu, especially using a compatible
string of a real device.

Please see my comments to patch 3/7 for an alternative idea.

Best regards,
Tomasz